Abstract

In oblique shock reflection, the effect of surface roughness is important. For example, the surface roughness delays the transition from regular to Mach reflection for weak shock reflection. The effect for strong shock reflection has not been investigated, so far as the authors are aware.
In the present paper, we investigated the effect of surface roughness for strong oblique shock reflection. The incident shock Mach number Mi was 1.915±0.005, and the reflection wedge angle ranged from 20° to 50°. The experiment was conducted with the shock tube in our institute. The driver gas was high-pressure helium, and the driven gas was air at atmospheric pressure and room temperature. The wave configuration was visualized by conventional shadowgraphy. The reflection configuration at any desired instant could be photographed by regulating a digital delay circuit. The coordinates (x, y) of the triple-point or reflection point and the angle between the incident and reflected shocks at the triple point were measured directly from photographic negatives using a profile projector.
For small reflecting wedge angles well below the transition wedge angle (50.5° for Mi = 1.915), Mach reflection was retained throughout, and the triple-point trajectory was regarded as a straight line through the wedge tip. For larger reflecting wedge angles that were smaller than the transition wedge angle, the reflection was regular in the early stage but later transitioned to Mach reflection, demonstrating that the surface roughness also delays the transition for strong shock reflection.
The behavior of wave angles is interesting. For smaller reflecting wedge angles (20°, 30°), the angles of incidence and reflection initially differ from the values given by von Neumann’s three-shock theory. However, the angle of reflection approaches the theoretical value from below the theoretical curve as the incident shock proceeds, and eventually the three-shock theory is satisfied. In contrast, the reflection angle approaches the theoretical value from above the theoretical curve for larger reflecting wedge angles.
In conclusion, oblique shock reflection over a rough surface is essentially unsteady but approaches the three-shock theory curve and attains pseudo-steady state in the end. Surface roughness delays the transition from regular to Mach reflection.

Strong oblique shock reflection, Surface roughness, Dynamic transition

In this paper the effect of inner flow characteristics has been studied by using numerical analysis. According to the flux change of the plate type heat exchanger which has a detachable Herringbone pattern, upon the temperature distribution and the pressure drop inside the plate type heat exchanger. The plate type heat exchanger is widely used in industries as it has an advantage of its high heat transfer efficiency and compactness. In this study a commercial numerical analysis program ANSYS CIX V14.0 was used to examine the inner flow pattern of a detachable Herringbone pattern which has a complicated and small flow space. Also the temperature distribution and the pressure drop amount were verified. Based on this, there is an improvement of inner pattern, decrease of pressure drop amount and the increase of heat transfer amount. This can be used as basic material to design the plate type heat transfer of detachable Herringbone pattern in the future.

plate type heat exchanger , numerical analysis, pressure drop, temperature distribution, flow distribution

In the present study, non-equilibrium molecular dynamics simulations are performed to explore the effects of wettability on gas-water flow over the roughness nanochannels. A “liquid-gas-vapor coexistence setup” is employed to maintain a constant thermodynamics state for individual equilibrium simulation and corresponded hydrodynamic case. The simulation systems are constructed through three stage: (a) initial condition, a sandwich-like cubic containing water and argon molecules are confined and stacked in the channel, (b) after the equilibrium simulation finished, the system reach a steady hydrostatic state and (c) the middle section is segmented out only along the x direction to form a flow configuration. An external force is applied along the x-direction to create a Poiesuille flow. Two control parameters are tuned, changing the properties of interest. (Ⅰ)To identify effects of interfacial gas density, the number of argon molecules is changed on initial setting. (Ⅱ)To simulate different wettability, the water-solid interaction energy is varied while the argon-solid interaction parameters are remained fixed. The fluid properties including hydrostatic and hydrodynamic states, such as potential energy (between water molecules and ambient particles), water and argon density contour, diffusion coefficients of water and argon molecules nearby the boundary regions, rotational diffusion of water molecules inside the cavities and effective slip length are visualized and analyzed. The present simulation results reveal that the regions with lower potential energy have higher possibility for water molecules location and thus increase the momentum exchange. Although no noticeable variation of density profiles, the argon diffusion coefficients adopt dramatic change nearby the roughened substrates after the external force added. We also examined the rotational diffusion coefficient and diffusion coefficient of the water dipoles inside the cavities. The present results show that the local translational and rotational diffusion coefficients of water inside the cavities are significantly influenced by the wall-fluid wettability. The results also show the effective slip length are both significantly influenced by wall-fluid wettability and interfacial gas density.

Molecular Dynamics Simulation, Wettability, Gas-Water Flow, Rough Wall Surface, Effective Slip Length

In the measurement of the wind velocity distribution of the air conditioner, a great deal of time and quantity of trouble are it in problems such as the need. The method that can improve these problems includes PIV, but is expensive. Therefore, using LED anemometer and Kinect, I aim at the offer of the system which can grasp wind velocity distribution intuitively by grasping space position and a wind velocity level visually and demand preparations trouble by the details measurement and a reduction effect for measurement time. I used the system which I developed for the wind velocity distribution measurement experiment of the air conditioner and examined the utility. As a result, it was cheap and knew that wind velocity distribution and the measurement of the quantity of wind were enabled by little time and labor by using a system.

Measurement,Wind velocity distribution,Air conditioner

The purpose of this work is to develop an innovative procedure for reconstructing the pressure field from PIV velocity measurements of unsteady, incompressible flows. The proposed technique is based on a generalization of the Glowinski-Pironneau method for the uncoupled solution of the incompressible Navier-Stokes equations written with primitive variables. The underlying mathematical formulation allows indeed to overcome some of the drawbacks affecting the techniques proposed so far in the literature, such as the use of ad hoc boundary conditions for the pressure and insufficient robustness with respect to measurement errors. The problem is discretized by Taylor-Hood finite elements and a Fortran90 solver is developed. The method is first applied on an exact solution of the Navier-Stokes equations, showing a second order convergence of the error for the pressure variable, measured in infinity norm. The robustness of the method with respect to the error in the velocity measurements is tested for both stochastic and deterministic perturbations. Then the proposed technique is applied to the PIV database of the flow around a pitching airfoil employed to investigate the dynamic stall. The computed pressure is compared with direct pressure measurements, showing very encouraging results.

Pressure field reconstruction, Particle Image Velocimetry (PIV), Uncoupled Navier-Stokes equations, Glowinski-Pironneau method, Finite Element Method (FEM), Dynamic stall.

This paper reports on a preliminary study of the flow features resulting from a shock wave propagating past a gap in a pipeline, using both experimental and numerical visualization. It represents a situation that may occur in an industrial accident. Tests were conducted in a simple shock tube with a 50mm internal diameter and 6mm wall thickness and gaps of 10, 20, and 30mm. Both a simple break in the pipe and where flanges become separated due to bolt failure were studied. The optical set up was a standard z-layout schlieren system with high-speed imaging using a Photron camera. Numerical simulations were run for an incident shock Mach number of 1.5. Both the internal flow and the flow features outside of the pipe were studied.
The simulations showed that, although the flow behind the incident shock is subsonic, the outflow resulted in it accelerating to supersonic speeds, similar to what occurs in a convergent-divergent nozzle. This resulted in a stationary shock wave developing at the inlet to the downstream section of pipe, essentially controlling the conditions of the propagation of the incident shock down this section, although its strength was significantly diminished from its original value. These standing shock waves were clearly seen in flow visualization for gaps of 20 and 30mm but turbulence in the 10mm gap prevented their identification. As the incident shock moves out into the gap a vortex ring follows, as is well known for an open-ended shock tube. However in the present case the shock propagates across the gap and reflects off the entrance to the downstream pipe entrance, this being particularly marked for a gap with flanges. The vortex ring then moves outwards into the external flow field which has been generated by the outward propagating toroidal shock wave resulting from the initial high pressure behind the incident shock as it passed through the gap. A second weaker vortex is generated as the flow passes over the inlet to the downstream pipe and interacts with the first one, eventually leapfrogging over it. A more complex interaction occurs in the gap with flanges with the primary vortex propagating up between the flanges before exiting into the outer flow field.

compressible flow; shock waves; vortices

For gas-liquid two-phase flow in horizontal pipe, slugging phenomena is undesired due to the flow stability and pressure fluctuation. Plug flow is acted as an initiation of the presence of slug flow. An image processing technique can be used to determine the flow pattern and flow characteristics from the input of flow visualization data. Sequences of images were digitally analyzed in order to investigate the important flow parameters based on study of interfacial behavior, flow topology, and bubble tracking.
This gas-liquid flow was recorded as video and extracted into sequences of images. The image processing technique including image conversion (RGB to Grayscale image), background subtraction, noise reduction (image filtering), image adjustment, image thresholding, and binarization resulted binary images that could be automatically analyzed by digital (1 and 0) logic, depended on the threshold value. A quantitative analysis were implemented that combined with statistical calculation to find important flow data. The elongated bubble velocity was determined based on the difference of bubble nose coordinate. Local analysis of each divided segment of image frame provided liquid film thickness data. The liquid hold-up data was determined by concentric analysis within gas and liquid thickness and real diameters. Real size of measurement were acknowledged by calibration procedure (pixel to millimeter)
As the results, an apparent interfacial behavior could be determined through this technique. The characteristics of elongated bubble (visualization results of bubble-nose and tail contours, elongated bubble velocity, liquid film thickness, and liquid hold up) were observed. A prominent result between visual experiment data and image-processing-based visualization produced a good agreement of flow pattern map of horizontal plug flow. It was found that the increase of gas superficial velocity (JG) and liquid superficial velocity (JL) would also increase the gas-bubble velocity. A comparison with the available previous studies was also carried out.

Plug flow, flow visualization, image processing technique, flow characteristics, elongated bubble

Many turbulent convection processes, in particular in nature, are present in extended layers and show hierarchies of regular ordered flow patterns although the corresponding Rayleigh (Ra) and Reynolds numbers suggest a fully developed turbulence. In this paper we want to present this spatio-temporal dynamics of large-scale structure formation in detail. Therefore, experiments with pressurized sulfur hexafluoride (SF6) will be combined with massively parallel direct numerical simulations based on a spectral element method. Both approaches will allow for convection studies in very large aspect ratio systems at Rayleigh numbers that were not accessible before. The analyses will clarify if such large-scale circulation patterns are relics persisting all the way from the onset of convection and the weakly nonlinear regime into the full turbulent regime.
First experimental results using PIV technique in a rectangular Rayleigh-Bènard cell with aspect ratio10 and Ra=3x105 were obtained in air under normal pressure. The cell consists of a cuboid with an electrical driven heating plate at the bottom and a water-filled cooling plate at the top. The optical access for measuring velocity field parallel to the heating and cooling plates of the cell was realized by using a semitransparent metal coated glass plate as bottom heating. Time-averaged flow fields show coherent large-scale flow structures in a very good agreement with numerical simulations at the same Ra and aspect ratio 12. We can observe local eddies, flow fronts and collision zones of flow pattern as well as rising thermal plumes. We want to identify the time scales on which the patterns evolve and investigate their Rayleigh number dependence. The experiment allows us to study the robustness of the flow patterns with respect to non-Boussinesq effects. Based on the experiments in SF6 and the simulations, we want to develop amplitude models which can describe the patterns by means of a few dominant degrees of freedom.

thermal convection, turbulence, large-scale structures, PIV, CFD

The work presented experimentally explores acoustic non linearities in a standing wave resonator using synchronized particle image velocimetry. As part of an ongoing investigation in the field of non linear acoustic propagation and thermoacoustic systems, it offers an innovative approach/design derived from the traditional PIV technique setup.
At high acoustic level, thermoacoustic systems bring a series of various non linear phenomena such as shock waves or development of acoustic streaming. The latter is used to describe the three-dimensional second order steady flow induced in any fluid flow that is dominated by its fluctuating components. It is superimposed on the first-order acoustic oscillations. One of the objectives of thermoacoustic studies is to improve the fundamental understanding of these nonlinear effects and in particular to determine there relative contributions leading to losses in thermoacoustic resonators (heat losses, pressure losses, etc.). Unfortunately, this goal is not so easy to achieve because these events usually lead to complicated theoretical descriptions where interactions between the different effects encountered are very present and not easily interpretable or measurable.
For the purpose of the study of nonlinear acoustic propagation a test bench was set up in the laboratory. It consists of a 5m long transparent half-wave resonator. To counteract any consequence of distortion of light through the walls of a cylindrical resonator section, a square section of 5cm² was preferred. A shaker, acting as acoustic source, provides a standing acoustic wave which frequency and displacement amplitude can be defined in order to satisfy the outbreak conditions of acoustic streaming. Two optical setup used for the PIV were implemented. The first one enables to observe and measure simultaneously two regions of the resonator. Through several mirrors whose orientation was chosen carefully, the images of the plane illuminated by the laser are reflected successively before being recorded simultaneously by the camera. Another setup creates the laser sheet and directs it towards the resonator. Both setups are connected so that they can slide united along the resonator.
The exploration of the acoustic velocity field achieved by the synchronized PIV technique enabled to highlight and quantify the phenomena appearing at these high acoustic levels and specially the development of 2 acoustic streaming cells along the whole resonator. These results also revealed the formation of a shock wave propagating from one end to the other of the resonator.

PIV, acoustic, non linearities, measurements

In order to secure the performance and the life time of electronic equipment with high heat fluxes, it is necessary to keep such a device under a critical temperature by introducing a high performance heat sink. To meet the recent demand for downsizing of the electronic application, the miniaturization and the improvement in heat transfer performance of the heat sink are required more strongly than ever. But it is known that the decrease in heat transfer area by downsizing causes a decline of the heat sink performance. From previous studies using large sized heat sinks, it has been revealed that the heat sink performance depends on the pin size, the population density of pin. However, as for the studies focusing on small sized heat sink, there seems almost no report to refer to. Accordingly, in this study, the effects of pin size, pin arrangement, pin shape and pin orientation on the heat transfer characteristics of heat sinks with miniature/micro pins have been investigated fundamentally.

Six types of heat sink models are proposed here. The first model named Type 1 has a single pin. In the following Type 2 model, the pin size is reduced to half the pin height and width of the Type 1 model. That is, under the condition of constant heat transfer area, the number of pins for Type 2 is quadrupled compared to Type 1. In the same way, six types of heat sinks in total, which have a pin height from several hundred micro meters to a few millimeters are prepared in this study. Concerning these heat sinks, we have tried to investigate the effects of the pin orientation (the upward, sideward and downward facings of the heated surface), the pin shape (the square and circle pillar) and the pin arrangement (the grid and staggered row) on their heat transfer performance by the numerical visualization of the flow and temperature fields near the micro pin fins.

From a series of numerical simulations, it has been clarified that the heat sink temperature rises with increase in the number of pins. Especially, contrary to expectations, the heat sink with miniaturized fine pins showed almost no effect on the heat transfer enhancement. This is because the choking phenomenon occurred in the air space among the pin fins. Concerning the effects of the pin orientation, shape and arrangement on the heat sink performance, almost similar tendency have been observed.

Numerical visualization, Heat transfer, Heat sink, Micro pin fin, Natural air-cooling

In this study, the vortex shedding characteristics and the flow patterns of vortex shedding from a pair of staggered arranged circular cylinders oscillating along the direction of flow were investigated by visualizing water flow experiment. The experiment was performed in a 4m3 closed circuit water channel in which a cylinder's oscillator was equipped on a carriage. The test cylinders are made from hollow aluminum with 16mm of outside diameters, 14mm caliber, 600mm length. A pair of tandem arranged circular cylinders is mounted on the oscillator and oscillates periodically to the direction of the flow. The flow visualization was done with the aid of the laser light sheet technique which was based on the dye injection method. In the plane of the laser light sheet at a depth of 140mm below the water surface, the flow was visualized by means of tracer ink (Rhodamine B or poster paint), which oozed out from two dye ports at plus-minus 60 degrees from the front stagnation point of the circular cylinder. The visualized flow feature was monitored by a CCD video camera and recorded on video tapes. The main experimental parameters given by frequency ratio f/fK (the ratio of cylinder oscillation frequency f to natural Karman vortex's frequency fK: f/fK=0~7), amplitude ratio 2a/d (the ratio of half amplitude of cylinder motion a to the outside diameter of cylinder d: 2a/d=0.25, 0.5, 0.75 and 1.0), distance ratio L/d (the ratio of cylinder distance L to the diameter of cylinder d: L/d=1.5, 2.5 and 5.5) and main flow velocity U=0.04m/s. The Reynolds number which is based on the main flow velocity U and the cylinder diameter d is 640. The mean vortex shedding frequency was measured by counting the visualized vortices for a certain time at the observation point. As the result of experiment, the variations of mean vortex shedding frequency were investigated. Also in the case of staggered arranged circular cylinders, the lock in phenomenon was observed. Even when a forced in-line oscillation was performed under the conditions in which two circular cylinders are carrying out mutual interference, it was found that a lock-in phenomenon occurs. The vortex shedding features were obtained and flow pattern distributions were shown.

Vortex, Wake, Separation, Lock-in, Flow Visualization, Staggered Arranged Cylinders

There have been numerous studies of the diffraction of a plane shock wave from the normal exit of a shock tube, including studies of tubes with square, lenticular, or other irregular exit shapes. However, in considering the practical case in which such diffraction may spontaneously occur (e.g. the propagation of a blast wave through climate conditioning ducts or of a shock wave through a tuned motor vehicle exhaust system), the more likely geometric boundary condition would be of a curved exit diffraction surface. The current study explored the diffraction of a plane shock wave from the curved exit of a shock tube with a boundary plate to remove the characteristic length of the shock tube thickness. The cases tested all had: separations between the axis of the curved plate and the shock tube axis of between 0.5 and 2.5 shock tube internal diameters; radius ratios of the exit surface to the shock tube inner diameter of 3 or 5; and Mach numbers ranging between 1.2 and 1.6. The flow field was visualised using a high-speed camera operating at 75 kfps capturing schlieren images. It was found that for the case of the exit surface tangent to the inner surface of the shock tube a vortex loop is not formed but rather a horseshoe vortex which convects downstream bound by the tangent exit plate. For non-tangent exits, vortex loops form comparable to those produced at the inclined plane exit of a shock tube. An additional feature was noted which is suspected of being the tangent view of a complex shock wave reflection due to the curved edge diffraction.

shock wave, vortex, diffraction

An experimental study on the interfacial behavior of stratified gas-liquid two-phase flow in a horizontal pipe had been conducted. It was originally aimed to determine the interfacial behavior of the flow and to develop a high quality database of it. The longitudinal section of transparent acrylic horizontal pipe (26 mm i.d.) was used as the reference section of image recording. Air and water were used as the test fluids, flowing cocurrently inside the pipe. The flow behavior was recorded by using a high-speed video camera around 5 m in axial distance from the inlet pipe to ensure the fully-developed stratified gas-liquid two-phase flow. To correct the refraction due to the acrylic pipe, correction box was used in the visualization test section. The group of stratified smooth and wavy two-phase flow was successfully recorded and classified on the basis of the visualization study from 24 couples of test condition of water and air superficial velocities. Digital image processing technique was then used to perform quantitative analysis and the results were used to evaluate the existing data. In the present study, the image processing technique was performed to obtain the liquid holdup distribution. From the results, the behavior of stratified smooth and wavy two-phase flow was clarified.

stratified gas-liquid two-phase flow, visualization study, interfacial behavior, liquid holdup, image processing technique

The effects of DC electric fields on flame behavior and soot formation were experimentally investigated for non-premixed ethylene flames in a counterflow burner. Experimental conditions were chosen with both soot formation oxidation (SFO) and soot formation (SF) flames, and applied intensities of electric field were varied from − 4 kV/cm to 4 kV/cm. We observed that the flames subjected to the DC electric fields moved toward the lower potential side due to ionic wind by Lorentz force, and the yellow luminosity from soot particles turned into reddish emission indicating changes in sooting characteristics. First of all, to clarify relation between ionic wind and the flame, the mie scattering method was adopted for flow visualization with electric fields. As the results, the ionic winds were generated from flame which is ion source to both anode and cathode plates, and then, double stagnation planes could be observed in counterflow configuration. Secondly, to analyze sooting characteristics under DC electric fields, planar laser induced incandescence (PLII) and fluorescence (PLIF) techniques were adopted to visualize soot and polycyclic aromatic hydrocarbons (PAHs), respectively. The intensities of PAHs were reduced around less than half of that of the flame with no electric fields. Moreover, no significant amount of PLII signal could be obtained due to the effects of DC electric fields. The detailed flame behavior and sooting characteristics with DC electric fields were discussed in this paper.

DC electric field, ionic wind, soot formation, counterflow diffustion flame

This keynote talk will highlight on-going studies of interactions between turbulence and complex topography. In general, laser-based measurements of such flow phenomena are challenged by topographical complexity, both due to laser reflections, which limits how close to a boundary one can measure, as well as optical aberrations, which can lead to high measurement uncertainties. To overcome these challenges of optical accessibility, we utilize a refractive-index-matching (RIM) approach whereby the refractive index of transparent models of complex topography is matched to that of the working fluid, thereby minimizing refractive index gradients responsible for these detrimental effects. This approach employs an aqueous solution of sodium iodide (~63% by weight), whose refractive index can be tuned carefully through temperature to match solid models fabricated from acrylic, in a recirculating flow tunnel. The RIM protocol has enabled planar and volumetric PIV measurements for a range of turbulence—complex-topography scenarios, including flow associated with interacting barchan dunes (sand dunes that form in unidirectional wind environments), turbulent boundary layers overlying porous, rough walls (representative of gravel river beds, for example) and flow around a replica of Gale Crater on Mars. The optically-unimpeded access afforded by this RIM methodology provides unique views of the rich flow dynamics associated with these turbulence–complex-topography interactions.

turbulence, PIV, complex topography, refractive-index-matching

Turbulent spot is a small turbulent patch, surrounded by laminar flow under boundary layer transition. It clearly shows a high ability in heat transfer over flat plate. Unfortunately, its behavior in early stage, called “young turbulent spot” is still less in information. In this paper, a finite difference approach, called “explicit method” and a developed image processing code were mutually employed to visualize images of young turbulent spot’s thermal footprints. The experiment of artificial young turbulent spots was carried out in low turbulent water tunnel using coated thermochromic liquid crystals. From obtained data, not only spot cerelities of leading and trailing edges, but also spreading half angle and propagation rates were informed. The spatial distribution on temperature, heat transfer coefficient, and heat flux are provided in each interval time. Streaky structure of young spot footprint is also clearly visualized. All achieved values are suitable for insertion into predictive formulas for full evolution of turbulent spot under bypassed transition flow.

Turbulent Spot, Boundary Layer Transition, Liquid Crystal, Visualization

We have examined the turbulence characteristics of fire plume with a ventilation-controlled pool fire through a PIV measurement. Research on the fire plume, especially near a pool, has been insufficient, while accurate descriptions of such structures are of practical interest, e.g., development of fire modeling in nuclear power plants. This might be owing to the extreme difficulty of velocity measurement for low-speed and high-temperature flow observed in the vicinity of a ventilation-controlled pool fire in experiments and the limitation of spatial resolutions of numerical simulations.

In the present study, we have carried out the velocity measurement by using a particle image velocimetry (PIV) technique with solid particles (spores of lycopodium clavatum, the diameter becomes several um in flame), the accuracy of which has been verified through the comparison with a hot-wire measurement (Hattori and Suto 2012). We have used the fire experimental apparatus, which has a capability to minutely control ventilation conditions in a compartment; the dimension of the compartment was 3.6 m (L) x 2.4 m (B) x 2.4 m (H) and the ventilation flow rate was 0.03m3s-1. We have dealt a pool fire in the compartment; the pool diameter and the fuel were 450 mm and ethanol, respectively.

After checking the basic fire parameters, such as time-series of heat release rate and O2 concentration in the lower and upper layers in the compartment, we have accumulated the measurements of turbulence statistics, such as turbulence intensities and Reynolds shear stress, and also investigated change in turbulence characteristics of the plume with the decreases in heat release rate and O2 concentrations; the normalized profiles of turbulence statistics in the plume is independent of heat release rate and O2 concentrations, allowing application of the similarity of flow fields for the ventilation-controlled pool fire.

We hope that our study, which provides the measurements of turbulence statistics and the understanding for basic characteristics of fire plume with a ventilation-controlled, will be helpful to develop fire models.

Buoyant Flow, Compartment Fire, High Temperature Flow, Plume, Turbulence

The oil-film interferometry skin friction technique is described and applied to subsonic and supersonic flows. The details for applying the technique are discussed. Results are shown for tests that illustrate the oil-film's good ability to measure the skin friction in a large scale. It is anticipated that continued development of this program will be necessary for use of oil-film technique to become widespread.

Oil Film Interferometry,Skin Friction,Image Processing

The investigation of complex combustion flows in turbo engine is the important content of propulsion technique. It is still very difficult for numerical simulation technique to predict the combustion flows accurately. This paper describes a measurement technique that can diagnose complex combustion flows based on general PIV technique to fulfill the measurement requirement of single head parts of turbo engine combustion chamber. Some techniques such as high pressure seeding particles, narrowband filtering lens, striding frames synchronizing shutter , air film for cooling and cleaning optical window are applied to solve the measurement problem of general PIV in high pressurecombustion flows. A new fluid measurement instrument is provided for the investigation of complex flowfield in combustion chamber of turbo engine. At the same time the velocity measurement results in combustion chamber in cold state and heating state are described in the paper.

combustion chamber，combustion flows，fluid measurement，PIV

Tomographic PIV allows the time resolved 3D 3C visualization of the flow field in a measurement volume. It is based on tracer particle reconstruction in a 3D voxel space. Due to the small size of Zooplankton, the whole body easily fits within the measurement volume, allowing, in principal, to capture the flow field all around the body. Problems arise in standard Tomographic PIV because the zooplankton body will be reconstructed as a huge tracer particle. Therefore, close to the moving object the correlation procedure for velocity calculation will lock on the reconstructed body features resulting in a biased calculated flow field close to the body that only represents the body movement rather than the desired flow of the fluid. Any interrogation volume touching the body surface will result in false flow velocity vectors, so that a large volume surrounding the body will give useless results.

Here a new solution for these problems is addressed: The zooplankton body and the tracer particles are reconstructed in two different reconstruction steps. Image processing is used to extract only the body shape in each camera image, getting rid of all tracer particles. This shape is used to reconstruct the 3D body shape using tomographic reconstruction (visual hull method, shape from silhouette). Due to a precise calibration, careful image preprocessing and a large camera angle (90°) it is possible to reconstruct even small body details like the antennas of the Daphnia, used in this experiments.

In the following reconstruction of the tracer particles, the determined body shape is used as a special reconstruction mask: voxel along the line of sight of a masked pixel will simply ignore the pixel of that camera. For each voxel the number of cameras that are not masked are counted. All voxel that are not masked by at least one camera will be reconstructed. However, only voxel that are not masked by at least 3 of the 4 cameras will be written to the output volume as valid voxel. Later, the correlation procedure will only calculate a valid vector if at least 50% of the voxel inside an interrogation volume are valid.

With this procedure the body shape can be visualized very precisely in 3D. On the other hand, the body is invisible in the second volume of reconstructed particle tracer, due to the advanced masking. Using also regions, where only 3 cameras can see the tracer particles allows the flow field calculation even close to the body.

Animated movies will be presented showing the time resolved 3D reconstruction of the body, the 3D 3C flow field all around and the 3D vorticity trace.

Tomographic PIV, Zooplankton Body Reconstruction

Emissions of carbon dioxide and nitrogen oxide are hot topics on environmental issues. We focus on lean combustion system of CH4/air mixtures as a measure to reduce emissions. Carbon content of CH4 is less than other hydrocarbon fuels, and nitrogen oxide (NOx) is less generated in the case of lean combustion whose flame temperature is lower than the case of stoichiometric combustion. However, diffusive-thermal instability appears in premixed flames with deficient CH4, because the mass diffusion exceeds the thermal diffusion. In this case, a cellular flame forms owing to intrinsic instability. For practical use, enough knowledge to control lean premixed flames with CH4/air mixtures is necessary. Therefore, we investigated lean CH4/air premixed flames previously, and it was found that the cellular flame forms on a flat burner and that the cell size increases with a decrease of equivalent ratio.
In this study, small amount of H2 was added to extend the lean combustion limit of CH4/air mixtures, and lean CH4/H2/air premixed flames on a flat burner were investigated. In the experiments, a lean premixed flame was observed from multi angles using a digital single-lens reflex camera (Canon Eos Kiss) and, a cross-sectional shape of a lean premixed flame was visualized by laser Rayleigh scattering. In order to evaluate the effects of equivalence ratio and H2 content, equivalence ratio ranges from unity to lower combustion limit, and H2 was added at 5vol%, 10vol% and 15vol% of CH4. As the results, the cell size of cellular flames decreases with an increase of equivalent ratio and of H2 content, and equivalence ratio at lean combustion limit decreases with an increase of hydrogen content. From these results, it was found that H2 addition extends the lean combustion limit and affects strongly the shape of cellular flame fronts. In a presentation, these images and results in detail will be reported.

CH4/air premixed flame, intrinsic instability, cellular flame, hydrogenation, flame behavior, high-speed video camera

The measurements for liquid fraction distribution of the high-pressure water jet utilized in the jet grouting were carried out by Laser Schlieren photography. The jet objected in this study is the water jet injected into the stagnant air with extremely high pressure and high flow rate. The flow pattern of the jet becomes water/air two-phase flow. The flow regime of the jet changes to various types; the continuous flow near nozzle exit region, and droplet flow far region from the nozzle exit. In order to evaluate the performance of the water jet, the radial density distribution or liquid fraction distribution of the jet is one of the most important parameters. However, no measurements have been carried out due to the very high speed (order of several hundred meters per sec) of the water jet. The authors have developed newly measurement system of liquid fraction distribution of high speed water jet using Laser Schlieren method. Laser beam is expanded to parallel beam and crosses the water jet. Then the beam is collected by lens and expanded again through pin hole and recorded by digital camera. From the two-dimensional recorded Schlieren image, the liquid fraction distribution in radial direction of the water jet is reconstructed by tomographic method. The experiments were carried out using high speed water jet of industrial use, the nozzle diameter is 1.7 mm, and pressure at outlet of nozzle is 0.1~20 MPa. The radial distributions of the liquid fraction were successfully obtained at various positions form nozzle exit.

High-speed water jet, Laser Schlieren photography, Liquid fraction distribution,

A curved-wall jet burner was developed and employed to stabilize turbulent premixed flames of methane/air, propane/air and ethylene/air mixtures. The motivated stability features of the current burner derive this study to investigate the turbulent scalar flux, of the reaction progress variable (c) and the flame surface density ("" ) with detailed spatial and temporal measurements. Simultaneous two-dimensional data of the velocity field and the relative OH concentration are obtained by time-resolved particle image velocimetry (PIV) and planar laser-induced fluorescence (PLIF) of the OH radical, respectively. Four flames for each fuel having different ratios of rms turbulent velocity (u^') to laminar flame speed (u_l) are considered that are representative of flamelet combustion regime. Data of the combined PIV/OH-PLIF measurements enable in obtaining conditional mean velocities in both reactant and product regions across the turbulent flame brush. The relative mean velocity of reactants and products, in axial, radial and normal direction to the flame front, provides an indication of whether turbulent diffusion of the mean progress variable occurs in the gradient or counter-gradient sense. The counter-gradient diffusion occurs when the flow field near the flame is dominated by thermal expansion due to flame reactivity, whereas gradient diffusion occurs when the flow field near the flame is dominated by the turbulent motions. Different flames reveal different turbulent transport properties depending up on u^'/u_l and flame heat release. Flame surface densities, are determined from the evaluation of the strongest gradient contours of OH intensity and its thickness, as a measure of the wrinkledness of turbulent flame fronts. The flame surface density at the burner centerline increases axially for higher Reynolds number (Re). Even though increasing Re increases spatially the flame front oscillatory (large turbulent flame brush), the peak value of "" is still comparable to that of lower Re. This is because high Re flames are relatively more wrinkled.

Turbulent premixed flames, PIV/OH-PLIF, turbulent scalar flux, Conditional Velocities, CWJ burner

Lifetime-based PSP measurement system was recently developed in TsAGI. System consists of two multi-gated (on chip accumulation) CCD cameras, UV-LED pulse illuminator and PtTFPP/FIB paint sensor.
PSP is illuminated by a pulsed LED array with square wave pulses. Paint luminescence is integrating in two gates during rise and decay of the luminescence by two cameras. The luminescence of the paint is a function of the paint thickness and illumination field. A ratio of the two gates is sensitive to pressure only. This allows pressure field calculation without collecting the 'wind off' images.
More common and simple intensity-based technique with two-color (binary) PSP cannot be applied to flows containing fog. Invisible to eyes small amount of fog can effect on measured pressure distribution due to light scattering dependence on light wavelength.
New developed PSP system is being tested at supersonic 0.6x0.6m wind tunnel T-113 (TsAGI). Tests are in progress now. Sonic boom pressure distribution from a tested model is measured on a flat plate installed at 0.1m over wind tunnel wall. Several methodical models are tested at Mach Number M=2.
The flow in this wind tunnel can contain water fog. First results demonstrate a feasibility of using lifetime method for supersonic flows containing fog.

PSP, Lifetime, sonic boom

Flow visualization has been an important tool for flight-testing. Many of the motivations are similar to ground testing, such as for flow diagnostics and to obtain a general understanding of the physics of a particular fluid flow. Flight-testing also typically involves full-scale studies, actual boundary conditions, and testing in the actual intended environment. Additional motivations of flow visualization for flight-testing include problem solving of unanticipated vehicle characteristics, understanding of scale effects, and other differences from ground test results (for example, wind tunnel) and computational fluid dynamics (CFD) predictions. The application of flow visualization to flight-testing is typically more challenging than that for ground testing although many of the same techniques are used. Techniques that have been successfully employed in flight-testing include infrared thermography, tufting (including flow cones), sublimating chemicals, liquid crystals, emitted dye, smoke, natural condensation, ground-to-air schlieren, and recently air-to-air synthetic schlieren techniques.

Flow visualization has been used for flight-testing for decades, but the original methods have evolved, and new methods have become available. Tufting and flow cones are one of the earliest and still most widely used methods in flight-testing. Tufts can show flow direction, relative turbulence of the flow, and indicate regions of separation. Smoke, oil flow, emitted fluid, and sublimating chemicals also have been used for some time and are still widely used techniques for flight-testing. Smoke reveals off-surface and 3-dimensional characteristics of a flow field, such as vortices. Oil and emitted fluid techniques shows surface flow direction, and sublimating chemicals reveal boundary layer transition. Sublimating chemicals show boundary layer transition. Liquid crystals show the effects of surface shear, such as from boundary layer transition. Infrared thermography has become a much more viable technique recently because of the availability of smaller and higher resolution infrared cameras. Infrared thermography also reveals boundary layer transition and any flow phenomena that create a measurable temperature change (for example, shock wave impingement). Synthetic schlieren methods recently have been applied to flight-testing. Synthetic schlieren techniques reveal shock waves and other density gradients, from distortions in the background behind the target. Improvements in the current techniques and the application of new methods continue to make flow visualization an important tool for flight research. A description of the techniques, including examples of the application of each, will be presented.

Background Oriented Schlieren, Supersonic Flow, Shock Waves, Air-to-Air Imaging

A flight test campaign of a supersonic natural laminar flow airfoil has been recently completed. The test surface was a 84-inch (213 cm) chord and 40-inch (102 cm) span article mounted on the centerline store location of an F-15 aircraft. The airfoil was designed with a leading edge sweep of effectively 0° to minimize cross flow. The test article surface was coated with an insulating material to avoid significant heat transfer from the test article structure and maintain a quasi-adiabatic wall. This avoids warm or cold wall conditions, which can significantly affect the boundary layer transition. An aircraft mounted infrared camera system was used to characterize boundary layer transition and thus the extent of laminar flow. Infrared thermography works well for characterizing shock wave impingement as well as boundary layer transition. The tests were flown up to Mach=2.0 and chord Reynold's numbers in excess of 30 million. The objectives of the test were to determine the extent of laminar flow at high Reynold's numbers and also to determine the sensitivity of the flow to disturbances. Both discrete (trip dots) and 2-D disturbances (forward facing steps) were tested. A series of oblique shocks, of yet unknown origin, appeared on the surface, which generated sufficient cross flow to dominate transition. Despite the unwanted cross flow the airfoil performed well. The results indicate the sensitivity of the airfoil to the disturbances, which can translate into manufacturing tolerances, were similar to that of subsonic natural laminar flow airfoils.

The infrared images clearly show the laminar-turbulent boundary layer transition and the subsequent movement with varying flight conditions. In addition the infrared images show the presence and movement of significant shock waves impinging on the test article surface. Images were captured in both analog and digital formats. Due to the placement of the camera and the optics (wide angle lens) there was considerable geometric distortion (foreshortening). Methods to process the images to reduce or remove the geometric distortion were applied to both the analog and digital images. In addition image processing schemes are being applied to the digital images to increase the visibility of the boundary layer transition and other significant flow phenomena such as shock waves.

supersonic natural laminar flow, infrared thermography, boundary layer transition, shock waves

Frequency responses of bubbles subject to oscillatory shear are experimentally investigated. We focus on the experimental range so that bubbles repeat yielding and shape recovery during each cycle of the shape oscillation. Two kinds of basic experiments have been carried out. One is velocity profiling of oscillatory bubbly liquid measured by ultrasound Doppler technique (UVP). In this experiment, bubbles are uniformly distributed in a cylindrical container which rotates in opposite direction at a given period. Capillary number, which is the ratio of viscous shear stress to the surface tension of bubble, is set around unity in order to assess non-Newtonian effective viscosity caused by transient bubble deformation. We have found with this measurement that the effective viscosity increases ten times as that in steady shear as the impact to the volume fraction of bubbles. Another experiment is high-speed photographing of the shape oscillation at frequencies higher than the resonance state. We have found that the phase shift of the shape oscillation reverses and bubbles start to traverse near a wall. These findings will be used for designs of improved drag reduction technique for turbulent boundary layer control by means of deformation-dominant bubbles.

Bubble, Interface, Rheology, Flow Control, Drag Reduction

It is often difficult to clearly extract the flow of humans and vehicles in a crowded scene, since overlap between people makes connected blobs subtracted by a background method. In our research, we regard this task as a maximum a posteriori (MAP) problem whose goal is to determine the configuration of binary-represented human-vehicle shapes that best explains the foreground masks. The MAP problem used in our research is trying to put a set of learned prototype shapes over the foreground masks, for the reason that we want to find the configuration that can best explains the foreground masks. We adopt the Reversible Jump Markov Chain Monte Carlo (RJMCMC) method to efficiently solve this MAP problem, which leads to the estimation of the number, locations, and shapes of humans and vehicles in the scene. That is, first we collect human and vehicle shapes which we call prototypes from training video sequences. Background subtraction is used here to obtain the binary data of these shapes, and we resize the prototypes to a normal size. We also define a posterior combining with a proper likelihood that can easily evaluate the configuration of the prototypes. The RJMCMC method is used because of the iterative sampling procedure. The RJMCMC method can offer many proposals to obtain a new state and decide whether to go or not to go to the new state by checking the value of the Metropolis-Hastings acceptance ratio. In our research we use three simple moves: birth, death and update. We start with an initial state and iterate the proposals at thousands of times to get a configuration that best explains the posterior. The number of the iteration times in the RJMCMC process is automatically learned because the large number of iterations is required when the scene is crowded. Good results have been obtained from many challenging data such as many available dataset or the scenes taken by ourselves. The major limitation of our method is its dependence on the background subtraction especially when the background is noisy.

Stochastic, Segmentation, MAP, Reversible Jump Markov Chain Monte Carlo, Sampling

Dynamic properties of particle distribution behaviors in the rolling circulating fluidized bed have been clarified by Electrical Capacitance Tomography (ECT). The amplitude and period of the rolling motion was varied from Θ=±π/18 to ±π/36 rad and T=5 to 15s, respectively. Limestone particles (Geldart group B) were used as the circulating particles. As results, in the case of the high superficial velocity, the rolling motion causes little impact to the flow directional profiles of particle volume fraction due to the relatively small inertial forces and changes of gravity component. As the decrease of superficial velocity, the fluid drag acting on particle decrease and particle volume fraction in the flow direction becomes fluctuate due to the influence of inertial forces and changes of gravity component. Moreover, the rolling motion has a dominant influence on the particle distribution un-uniformity in the radial direction. An obvious periodical variation of the particle volume fraction appears under the rolling motion whereas this phenomenon did not appear under the upright condition in any previous studies. The time-dependent resultant force of the gravity component and inertial forces and the high Stokes number is proposed to be the primary influencing factor for the un-uniform radial profiles of particle distribution in the CFB under the rolling motion.

Rolling angular velocity; Inertial forces; Electrical capacitance tomography

In fusion welding, gravity makes a molten metal flow downward and it sometimes causes an irregular-shaped weld bead and weld defects,　especially in horizontal and overhead positions.
To solve this problem, Manabe et al. proposed a basic concept of "Electromagnetic Controlled Molten Pool Welding Process (ECMP) ". In this process, the molten metal flow and the bead shape were controlled by using upward electromagnetic force generated in the molten pool by the magnetic field perpendicular to the unidirectional current.
Based on this concept, the ECMP method, in which the magnetic field coaxial to a welding torch is used, has already been put into practical use for thick plate multipass welding in horizontal and vertical positions of a LNG tank with a high-deposition rate of 2 to 3 times higher than those of the past.
One-side welding without a backing is desired for welding a small diameter pipe or a structure in which a welder is unable to enter inside. In conventional one-side welding without a backing, the shape of the backside of a penetration welding becomes excessively convex downward in flat position welding and yields an undercut defect in the backside of a weld in overhead position welding. Although the ECMP method described above is considered very promising as a means of resolving the problems, it is inapplicable to flat and overhead position welding in principle.
Therefore, in flat and overhead position welding, the authors proposed a new ECMP method using a new magnetization coil which is installed in the back side of the torch, so that the weld line can be straddled by the coils, and the applicability of this new method to industry was examined.
However, when magnetic flux density was increased, the arc shape and the molten metal flow became unstable occasionally, and then the weld defects occurred.
In order to expand the region of applicability of the new ECMP method, the flow and the temperature of molten metal under different parameters (Magnetic flux density, Wire current, etc.) was observed in detail. The molten metal flow was visualized by using the Pulse Laser (λ=810nm), which has a maximum power of 500W. Also two-color temperature radiometry utilizing color high-speed camera was used to obtain the surface temperature of the molten metal.
As a result, the effect of different parameters on the flow and the temperature of molten metal during the ECMP method could be recognized.

Molten Pool, Arc Welding, Electromagnetic Controlled Welding,Two-color temperature radiometry, High-speed camera

Flow separation and reattachment occurs frequently inside and around various equipments for engineering purpose. A typical example is the flow around an orifice in a pipe, which is often used as a flowmeter. This flow causes the mass transfer enhancement at downstream of the orifice, and sometimes causes the pipe wall thinning due to the flow accelerated corrosion. Thus, it is important to investigate the mechanism of the heat and mass transfer around an orifice to provide information for resolving such a problem.
In this study, the turbulent heat transfer was measured around an orifice in a water pipe flow. In the previous report, we developed a technique to measure the spatio-temporal heat transfer distribution in a horizontal pipe flow by employing a technique using high-speed infrared thermograph (Shiibara et al., Proceeding of the 9th PSFVIP, pp. 303-308, 2013). The main purpose of this experiment is to confirm whether the technique using infrared thermography is possible to measure the spatio-temporal heat transfer for a highly complicated flow with flow separation and reattachment.
The measurement was performed using the experimental setup of a water flow in a horizontal pipe with inner diameter of D = 20.4 mm. An orifice plate (bore diameter of d = 10.0 mm) was set in the test section. The Reynolds number based on D ranged from 1000 to 13000. The test surface for the heat transfer measurement was fabricated from a titanium foil of 20.7 μm thick coated with black paint, which was heated electrically under conditions of constant heat flux. The temperature distribution and its fluctuation appeared on the test surface were measured using infrared thermograph.
As a result, the temperature fluctuation due to the turbulent heat transfer was successfully visualized. At the upstream of the orifice plate, the thermal streaks appeared similar to that of the fully developed pipe flow. At the downstream of the orifice plate, the heat transfer was much enhanced, which seems to be related to the highly complicated flow due to the flow reattachment.
From the measured temperature, the quantitative heat transfer coefficient, which fluctuated complicatedly with time and space, was evaluated. The time averaged Nusselt number distribution along the streamwise direction agreed well with the previous experiment (Krall and Sparrow, Journal of Heat Transfer, pp. 131-136, 1966). This indicates that the quantitative measurement is possible at least for the time-averaged value using the technique proposed here even if the heat transfer varies complicatedly with time and space.

Turbulent heat transfer, Infrared thermography, Spatio-temporal measurement, Circular pipe, Orifice

We study alternating droplet generation at a cross-junction during multiphase flow in microfluidic channels. We examine the efficiency of generating alternating droplets and the monodispersity of water-in-oil droplets for various cross-junction shapes, from a straight channel to a tapered channel. Furthermore, we investigate the effect of capillary number by varying flow rates and surface tension, and the viscosity ratio of water and oil. To understand the flow field at the cross-junction during the alternating droplet generation, we perform PIV measurements in the oil and water phases. In the straight cross-junction case, we observe a significant backflow of the water-phase after the droplet is pinched off. This backflow and interruption by the other droplet generated from the opposite side of the channel cause the polydispersity of the resulting droplets. However, if the water-phase inlet has a tapered shape, the backflow along the channel is weak, and the efficiency of forming alternating drops is high for a wide range of capillary numbers. From the flow field measurements, we found that an upstream flow field of the water phase varies depending on the channel shape, and results in different pressure buildup and perturbation behaviors at the cross-junction. From the flow field measurements, we obtain the instantaneous pressure distributions, which is obtained by an iterative integration method of the pressure gradient term in the Navier-Stokes equations. Based on the analysis of the internal pressure distributions and the flow fields, we provide an optimized shape of the cross-junction to produce mono-dispersed alternating droplets with various flow rates and fluid properties.

PIV, Multiphase, Alternating droplet generation, Microfluidics

Concerning the visualization method for the temperature field of a still or flowing gas, thermographical method, Mach-Zehnder interferometer method and so on could be given for representative examples. In these methods, however, high setup costs and/or hard-to-use operational skills are usually required. Accordingly, when it comes to obtain an approximate gas temperature field simply and quickly, such kinds of methods are not necessarily suitable.

To cope with this problem, a simple, inexpensive, and user-friendly visualization method for the temperature field of heated air flow has been proposed in our previous study. The visualization system is composed of a hot air generator, a buffer box to form a stable air flow, a circular nozzle, a mesh screen on which the hot air flow image is projected, and a thermograph with which the temperature field and the flow zone are simultaneously observed. From fundamental experiments, the proposed method has been shown effective for visualizing the hot air temperature field.

In order to obtain more quantitative temperature field, however, the reliable apparent emissivity of the mesh screen must be given. Therefore, in this study, the apparent emissivity of the black coloured net with low thermal conductivity, which was used as the mesh screen, has been evaluated experimentally. In the present study, two kinds of nets have been tested, that is, the one is made of polypropylene resin, and the other polyethylene. The apparent emissivity of each net has been evaluated by making the axial temperature distribution of hot air flow measured with the thermograph fit the one measured using sheathed thermocouples by changing the emissivity of the thermograph. From a series of experiments, the relation between the apparent emissivity and the aperture ratio (or the porosity) has been clarified for the black coloured polypropylene and polyethylene nets.

Visualization method, Temperature field, Thermograph, Mesh screen, Apparent emissivity

The marine microorganisms brought by ship ballast water through worldwide ship traffic have made a severe threat to marine ecosystem. In order to reduce and eliminate unfavorable marine microorganisms safely and economically, a sterilization method using microbubbles and underwater shock waves have been studying. The underwater shock wave has been widely applied into various fields like medical science, engineering, and food science. As the energy sources of underwater shock wave generation, electric discharge, micro-explosives, pulsed laser beam or high-speed impacts of projectile are generally used. However, these energy sources are not convenient to be introduced directly into the ship ballast water treatment with safe and easy operation, cost savings, and energy savings. Therefore, considering generation of shock waves on board, the exhaust gas from the main engine and electric generators will be the driver gas of a shock tube. In the present study, a diaphragmless shock wave generator assisted by magnetic force was designed as a driver device to generate underwater shock waves on the assumption of exhaust gas utilization.
This paper reports on a new method with respect to generation of underwater shock waves. We try to produce underwater shock waves using elastic materials connecting with the diaphragmless shock wave generator. Driver gas in the high-pressure chamber of shock wave generator is used 0.4-0.6 MPa air, and the measured propagation velocity of a shock wave in a 10 mm-diameter shock tube is around 1.5 of Mach number. The elastic material, such as a silicone tube, connected with the shock tube exit is placed under or over water surface. The visualization experiment is carried out by schlieren method. We confirm shock waves and flow structure discharged from the shock tube exit, and observe the shock wave interaction with water surface. In addition, wave production in water generated by rapid deformation or impact on water surface of a silicone tube is investigated. On the other hand, from the analysis of the underwater shock pressure generated by collapse of a 10 mm-diameter bubble, it is found that the acceleration of 1507 m/s2 is required to obtain 0.5 MPa of pressure behind an underwater shock wave. This result will be an estimation of deformation speed of elastic medium to produce much stronger underwater shock wave.

Underwater shock wave Generation, Elastic material, Schlieren method, Diaphragmless shock wave generator

Ignition of combustible mixtures by transient turbulent hot gas jets is an important phenomenon in many devices, either as a safety issue but also as a means of initiating desired combustion. The processes leading to and taking place during ignition by hot free jets are complex, involving chemical reactions coupled with energy and mass transport during turbulent mixing of exhaust and fresh gas. This complex chemistry/turbulence interaction also aggravates their systematic experimental investigation. In order to isolate the effects of flow and molecular transport from the chemical reactions, non-reacting helium/nitrogen-jets impinging into a nitrogen atmosphere are investigated. Within this study, spatially resolved laser-based measurements of instantaneous mixture fraction fields at an isothermal transient gaseous turbulent free jet impinging into a quiescent atmosphere are conducted. The mixing process is studied by means of planar laser induced fluorescence (PLIF) using nitric oxide (NO) as a tracer molecule. By repeating the experiment many times for nominally identical initial and boundary conditions, statistics on the turbulent mixing field can be obtained from the experiments. The paper gives an overview of the experimental set-up used to investigate the mixing processes of repeatable transient free jets with the quiescent ambiance in an optically accessible gas cell. Strategies for obtaining quantitative mixture fraction fields from the measured PLIF-images are explained and image-processing techniques are outlined.

turbulence, laser-induced fluorescence, transient free jet

Control of flow around a circular cylinder by the synthetic jets positioned near the separation points has been experimentally investigated in a water tunnel with flow visualization and particle image velocimetry (PIV) techniques. A hollow circular cylinder with outer diameter D = 30 mm and inner diameter d = 24 mm was horizontally mounted across the test section. End plates were used in order to maintain the two dimensionality of the flow field, leaving an extended circular cylinder with a spanwise length of 450 mm and an aspect ratio of 15. Two slots with width w = 1 mm and length l = 100 mm were arranged on the external surface of the experimental cylinder in the mid-span region at azimuth α = ±85° from the front stagnation line, which were used as the slots of the synthetic jets. For the present investigation, the free-stream velocity was fixed at U∞ = 44.6 mm/s, corresponding to the cylinder Reynolds number Re = 1300 and the natural shedding frequency f0 = 0.3 Hz (St = 0.2). A variety of wake vortex shedding modes have been recognized when the excitation frequency is varied as different multiples of the natural frequency. Besides of the asymmetric 2S mode when the wake vortex are shedding alternatively from both sides of the circular cylinder for the natural case, the symmetric 2P vortex shedding mode, the symmetric 2S mode and the asymmetric 2(P+S) mode are also observed. There exist cases in which the symmetric and asymmetric 2S modes compete with each other, resulting in the formation of the bistable shedding state. Statistic characteristics of the flow field such as time averaged vorticity and velocity based on the PIV data have also been compared to distinguish the differences between the symmetric and asymmetric modes..

Synthetic jet, Circular cylinder, Shedding mode,

An acoustic tube was designed and implemented in turbulent shear flow over a backward-facing step. The objective of the acoustic tube was to suppress the flow separation behind the step and reduce the reattachment length. As an active flow control device, the acoustic tube generated periodic small perturbations which educed coherent structures into the shear layer. The acoustic tube consisted of a spanwise tube with square cross-section and a thin slot in the center. One side of the tube was mounted with a loudspeaker, while, the other side was sealed. When the wave length of sound fitted in the tube, standing waves therefore existed as well as fixed anti-nodes with pressure peaks and valleys. The slot on the backward side was used to educe periodic perturbations outward.

Standard particle image velocimetry (2D-2C PIV) was employed and the region of interest was 310×70 mm in x- and y- direction respectively, which covered the turbulent boundary layer in the step region, the separated shear layer and the reattachment area. A high-resolution camera pco.4000 was mounted outside the flow field to record images with an array size of 3900×910 pixel. The flow was illuminated by a vertical laser light sheet with 1mm thickness from downstream orientation.

Time-averaged and phase-averaged flow fields were recorded in clean and controlled cases. In controlled case, it has been shown that the flow separation was suppressed and the reattachment length was reduced by 44.3%. The consecutive phase-locked results provided the generation, entrainment and dissipation of shedding vortices and the development of periodic motions in the turbulent shear layer. Besides, two-point spatial correlations at discrete points downstream reveal the shape of growing shear layer and the coherent features. The Reynolds shear stress <u'v'> was increased and had higher values correspondingly where coherent structures were educed, entrained and dissipated. These coherent structures eventually enhanced the momentum transfer and consequently conveyed kinetic energy from the mean flow to the fluctuating motions. Furthermore, Proper Orthogonal Decomposition (POD) was applied to the uncorrelated PIV snapshots to extract large-scale organized structures depending on their kinetic energy. After removing higher order modes, the phase-averaged flow fields that reconstructed by the first two modes provided clear insight into the evolution of the coherent structures as well as the interaction between the mean and periodic flow fields.

coherent structure, active flow control, backward-facing step, PIV, POD

A high speed visualization study on droplet impinging characteristics on a smooth sapphire substrate was conducted. Characteristics map of dynamic behaviors of droplet impingement was obtained in the ranges of surface temperature, Weber number and inclination angles. The sapphire plate was heated up to 300ºC by a cartridge heater. De-ionized water droplet was made through a 31G injection needle and the droplet size was 2.3mm. Two high speed cameras were used for side and bottom visualization, and the frame rate was 20000 fps. Weber number was changed from 6.19 to 136.16 by adjusting initial height of the droplet from 40 mm to 210 mm. Inclination angles were varied from 0 to 60 degrees. Dynamic behavior of droplet after impingement was strongly depended on inclination angle, surface temperature and Weber number. Micro-explosion was observed in case of high Weber number at Leidenfrost condition. In case of lower inclination angle, the impinging droplet tended to recover its original spherical shape due to the vapor cushion at Lidenfrost condition. As increasing Weber number, both maximum spreading diameter and slip length were increased.

Weber number, Leidenfrost phenomenon, Inclined plate, Visualization

An experimental study has been conducted for wings with sinusoidal leading-edge modifications at low Reynolds numbers. In the earlier studies conducted by Johari et al. (2007), post-stall performance of leading-edge modified wings are more favourable than non-modified wings, where the deterioration in the lift coefficient is considerably lower beyond the stall angle. Subsequent studies have demonstrated that these favourable behaviours are due to the presence of peaks and troughs along the leading-edge, where they lead to the formation of counter-rotating streamwise vortices. These streamwise vortices are able to reduce the extent of flow separations by energizing the surface boundary layers. However, it should be noted that these earlier studies on leading-edge modified wings were typically conducted at relatively high Reynolds numbers. For MAV flights where Reynolds numbers are much lower and hence more prone towards flow separations, whether these leading-edge modifications are still able to reduce flow separation effects remains to be seen. Hence, the motivation behind the present study is to investigate the efficacy of these modified wings at a significantly lower Reynolds number.

In the present study, NACA634-021 wings with leading-edge modifications were studied in a low-speed recirculating water tunnel at Re=14,000, which is about an order of magnitude smaller than previous studies. Leading-edge modified wings with wave-amplitude to chord ratio of a/c=0.12 and wavelength to chord ratio of λ/c=0.25 and 0.5 respectively were investigated. Particle-streak photography was used to assess the formation of the streamwise vortices and their influences upon the flow separation regions. On the other hand, digital particle-image velocimetry was also used to capture the velocity fields. Streamwise results show that the leading-edge modified wings are able to reduce the flow separation region sizes along both the trough and peak locations up to an angle-of-attack of α=20º. Furthermore, flow separation events along the peak locations are delayed till more downstream locations up to α=20º as well, as compared to the trough locations and non-modified wing at similar angles-of-attack. In this case, it should be highlighted that the flow separates in an abrupt manner when it does. Cross-stream results demonstrate that the leading-edge modifications produce highly coherent streamwise vortices that exerts considerable effects upon the flow fields, with evidences pointing towards them being responsible for the reduced flow separations observed here. Hence, it would appear that leading-edge modified wings may be useful at low Reynolds numbers as well to suppress early flow separations.

leading-edge modified wings, flow separation control, flow visualization, particle image velocimetry

This research explores the air flow and forced convective heat transfer on a heat sink with biomimetic oscillating foil. Experiments were conducted to measure the thermal resistance for various angular velocity distributions of foil at different oscillating frequencies. A mechanism with cam, linkage, and foil was established to form flapping motion with specific angular velocity distributions, including fast forward/slow backward, uniform, and sinusoidal profiles. Air flow in a duct was driven by the foil oscillation and caused heat dissipation from heat sink mounted on a heat source. The heat source has dimension of 2.5cm2.5cm. The heat flux is 10kW/m2. The oscillating frequency ranges from 1Hz to 7Hz. The flow rate and thermal performance were measured. The results indicate that the angular velocity profile of fast forward/slow backward results in higher volume flow rate and lower thermal resistance. Besides, the flow structure was observed with PIV technology. Main stream resulted from reverse Karman street was found.

oscillating foil, Strouhal number, angular velocity profile, thermal resistance

We propose a computer vision based system that traces human flows and actions, and detects objects left and/or moved by these actions. That is, it finds the objects brought in or taken away by the human works. Recently, many surveillance cameras are working and they are utilized to improve our safety life. Some of these cameras have intelligent facilities such as a detection function of human’s abnormal actions trying to enter a prohibited area. In this study, we assume that the human actions make the left and/or moved objects. Then we compare the images before and after the actions and identify left and/or moved objects. A background subtraction method is used to extract segments of humans and objects from image data. In order to estimate humanless background images even under the condition that frequent entries, exits and walks occur, an advanced dynamic background subtraction method is developed. The system consists of a global camera and some local pan-tilt-zoom cameras. The global camera covers a wide scene, finds humans’ flows and notifies the local cameras the positions where the actions of the humans occur. The local camera focuses on the position indicated by the global camera and tries to find whether there are any left and/or moved objects. Two kinds of human motions are expected: one is the walking or passing and the other is the one appearing in a limited image area (e.g. desk work). The differentiation between the humans’ segments and objects’ segments is based on the fact that the center points of the humans’ segments always drift and the objects’ segments unchanged. Experiments have been carried out in the sunlit room (7 m x 6 m). Correctly and incorrectly detected left and/or moved objects and the objects that are detected but not left and/or moved are named correct objects, incorrect objects and erroneous objects, respectively. The fraction of the number of the correct objects to the number of the really left and/or moved objects is about 80%, and a reasonable performance is attained. The proposed system can be applied to build a comfortable ubiquitous environment.

human flow, object detection, left object, moved object, computer vision

An animal is adapted for ecology in process of evolution, and is carrying out various forms.

it is thought that they perform the walk efficient way in accordance with their forms.

in this research,we have focused on the movement of the center of gravity of the four-legged animal walking

Dynamic analysis, center of gravity movement

In this research, a proper orthogonal decomposition (POD) based data reconstruction approach is applied to PIV data around a flapping wing object. Since we have interests in its hovering condition, particles (smoke in this study) cannot be supplied along uniform flows. The smoke is, therefore, just scattered around the flapping wing object, which makes some missing regions of the particles in the flowfield. This finally yields the failures of PIV measurement at considerable regions of flowfield at the hovering condition. Since it is difficult to control the scatter of the smoke with a certain level of repeatability, some other approaches are essential for its robust PIV measurement.
To overcome such difficulties, the POD-based data reconstruction approach is applied to the gappy PIV data around the flapping wing object. By using the POD, dominant modes (flow structures) can be extracted from large scale temporal/spatial data. The gappy PIV data can be reconstructed from the dominant modes of the gappy PIV data itself. In this research, the accuracy of the POD-based reconstruction method is investigated by using a cross validation approach.
Recently, the development of advanced unmanned micro air vehicles (MAV) is watched with keen interest for the observation/exploration at risky/ultimate environments. For that reason, we have self-developed a flapping wing object to understand the detailed flow physics around the flapping wing. Our flapping wing object can achieve to flap at 5Hz with several feathering motions of the wing. These detailed flow/vortex structures are investigated in this research with the developed POD-based PIV data reconstruction approach.
The effectiveness of the developed POD-based PIV data reconstruction was confirmed by the cross validation analysis, in which some parts of the exact PIV data were intentionally hidden to compare with the reconstructed PIV data. The POD-based PIV data reconstruction was much more accurate than time-averaged simple reconstruction. The leading edge vortex (LEV) as well as trailing edge vortex (TEV) were accurately captured by the reconstruction, that are typical flow structures around flapping wings. By introducing the feathering motions, induced velocities to the downstream/lower directions were confirmed, which implies the generation of lift/thrust forces by the feathering motions.
Thus, the validity of the POD-based PIV data reconstruction was confirmed and then the detailed flow physics are being investigated. By additional PIV measurements at various sections around the flapping wing object, three dimensional flow structures around the flapping wing object will be revealed in this research.

PIV, proper orthogonal decomposition, flapping wing object, cross validation

Bubble injection is an effective technique for reducing the frictional drag of ships. However, the total frictional drag reduction does not always happen when injected bubbles separates from the ship's bottom and are involved in the ship's screws. Therefore, we need to accurately control the bubble motion in order to reduce the skin frictional drag effectively. In this study, with the final goal of an accurate control of the wall-sliding bubble motion, we investigate this effect on the wall surface condition.
In our experimental apparatus, the liquid circulates through a horizontal channel (test section), a magnet pump and a electro-magnetic flow meter. The horizontal channel is made of transparent acrylic resin, and it has 1,600 mm long, 100 mm wide, and 10 mm high. Tap water is used as the working liquid. Air bubbles are injected through 5 needles installed on the upper inner wall, and the bubble flow rate is controlled by using a tube pump. The Reynolds number of the working liquid is defined as Re=UH/n, where U is the bulk mean liquid velocity, H is the height of the horizontal channel and n is the kinematic viscosity of the liquid. For a constant bubble flow rate, the conclusions obtained from the bubble diameter and velocity measurements are: (1) As the wettability of the upper inner wall surface increases, the bubble diameter and the streamwise bubble velocity tend to increase. In particular, this tendency is more clear at Re=1000 than at Re=3000. (2) At Re=1000 and 1500, the use of the functional surface that consists partially of the hydrophobic and super-hydrophilic parts is very effective for controlling the wall-sliding bubble motion.

bubble injection, drag reduction, visualization

Shear stress diagnostics in aerodynamic tests can be performed using thin-film coatings based on optically-active liquid crystals (LC) which are sensitive to shear stress. These coatings do not change the model geometry and can be easily applied on the investigated surface including metal models.
Two main methods of using liquid crystal mixtures for shear stress diagnostics are investigated in this work.
The first method is based on texture transformation (from color-less focal-conic to colored planar) of cholesteric liquid crystals under shear stress. This process is irreversible and the method is based on the time of color appearance.
The second method is based on selective reflection of the white light falling on the liquid crystal with a planar texture. The dominant wavelength of the reflected light is dependent on the pitch of the structural helix of the LC coating. Under the shear stress induced by the flow structural helix changes and the dominant wavelength of the reflected light shifts to shorter wavelengths region. It is essential that the wavelength shift is proportional to the value of the shear stress and it allows visualization of the surface flow.
So in both cases the experimental procedure is based on the registration of the LC response to the shear stress induced by the flow.
The key aspects of the method are choosing the optimal liquid crystal coating and providing shear stress visualization at the investigated surface at the observation angles defined by the windows in the walls of the wind tunnel test section.
Three series of tests have been performed on metal models at subsonic and transonic flow velocities in the wind tunnels T-128 and T-103 (TsAGI). Using the method of shear stress sensitive liquid crystals visualization of laminar-turbulent transition, flow separation and shock waves was successfully performed. Experiments showed that liquid crystals are a promise for panoramic shear stress diagnostics.

liquid crystals, shear stress, laminar-turbulent transition, flow visualization

We introduce a dual-luminescent imaging to capture time-resolved temperature maps of water mixing process. It uses two luminescent probes; one is sensitive to the temperature and the other is insensitive to the temperature. The luminescent images from these probes are simultaneously captured by a high-speed color camera. By simply taking the ratio of the two luminescent images, we can extract the time-resolved temperature information of a target object. We focused on the water mixing process as the target object. Other temperature measurement methods, such as a thermocouple or an infra-red camera, have limitations to capture the time-resolved mixing process. Because a conventional thermocouple is relatively large to resolve the mixing process, it is not an appropriate method to capture the time resolved information. It also creates a flow disturbance. An infra-red camera can be used as a non-intrusive technique. However, it integrates the whole water volume that gives averaged information of the mixing. With a laser sheet illumination, a 2-D profile of the mixing process can be visualized and quantified to the temperature values by using the dual-luminescent imaging. We mixed water with two different temperatures. A description of the dual-luminescent imaging is included in the final paper, as well as the time-resolved measurements of the mixing process.

Multiphase Flow

We apply pressure sensitive paint (PSP) to quantitative analysis of pressure distribution and visualization of shockwave structures on a sidewall in a supersonic flow passing through a turbine cascade, to examine the performance of the rotor blades for the last stage of steam turbine. However, temperature dependence of PSP may make large error for pressure measurement of solid surfaces, if they have non-uniform temperature distribution. This error becomes significant issue when PSP is applied to surfaces in supersonic flows with shockwaves because of large non-uniformity of the temperature distribution on the surfaces. We apply dual-layer PSP/TSP, the combination method of PSP and temperature sensitive paint (TSP), to increase the accuracy of pressure measurement by compensating for the temperature dependence of PSP by using the temperature distribution measured by TSP. The luminescence images of PSP and TSP are taken simultaneously by using two high-speed video cameras with different optical filters to separate the luminescence of the each paint with different wavelength. Accuracy of the pressure measurement of the sidewall with non-uniform temperature distribution by the dual-layer PSP/TSP is examined in the supersonic wind tunnel tests, by comparing the pressure data obtained by the dual-layer PSP/TSP with those measured by pressure taps. The temperature distribution on the sidewall measured by the TSP component shows large non-uniformity caused by shockwave structure, especially on the side of the suction surfaces of the blades. In this case, the pressure distribution on the sidewall measured by the PSP component shows the average error of as large as approximately 30% without temperature compensation. The error is reduced to less than 10% by the compensation using the temperature distribution obtained by the TSP component. The residual small error may be caused by the temperature difference between the PSP layer and the TSP layer. In addition, the shockwave structures visualized by the dual-layer PSP/TSP is compared with those obtained by the schlieren photograph. There is slight difference in shock angles between the two on the side of the suction surfaces with relatively high Mach number. On the other hand, the difference in the shock angles on the side of the pressure surfaces is smaller, while the shock structure obtained by the PSP blur. This is because the PSP visualizes the shockwave structure close to the sidewall while the schlieren photograph visualizes the shock structure in the mainstream.

Dual-layer PSP/TSP, Turbine Cascade, Supersonic Flow, Shockwave

Jet flows have been applied in numerous fields to control flow separation. In many cases, a continuous jet is utilized and it is generated by a heavy turbomachine consisting of many parts including a rotor, stator, and casing, as well as a driving source. Therefore, it is difficult to downsize the entire system. As an alternative to continuous jets, synthetic jets which are generated by a compact actuator (i.e. piezoelectric actuation, piston, diaphragm, or speaker) have attracted attention in recent years. However, these synthetic jet actuators are still at the research stage and much remains unknown including the relation between the flow characteristics and the drive system of the actuators. In particular, there have been no detailed reports on the relation in the case of a synthetic jet actuator using nonlinear oscillation.
This study attempted to clarify the effect of nonlinear oscillation (mathematical modeling of the motion of bubbles produced by electric discharge) on the flow characteristics of synthetic jets by conducting an experiment and numerical analysis. The onset condition based on the non-dimensional stroke of the synthetic jet and the relation between the nonlinear oscillation and the change of jet velocity along the axis of the jet are discussed. Especially, the influence of T* (the ratio of driving time of the actuator to the down time) on the unsteady flow pattern and the time-averaged jet structure is investigated. The unsteady flow patterns of synthetic jets are also compared by using the results of a visualization experiment and numerical simulation. Furthermore, the flow characteristics of synthetic jets generated by non-linear oscillation are compared with those of a normal synthetic jet produced by linear oscillation under the equivalent stroke.

continuous jet, synthetic jet, nonlinear oscillation, unsteady flow, velocity distribution

In this study, the transient behavior of liquid film and the flow of inner gas after bursting of a soap bubble was investigated. To visualize the transient behavior of the soap bubble after rupturing, a pulse laser was used for noncontact rupturing of the soap bubble. The olive oil particles were supplied into the soap bubble through a Laskine nozzle for visualization and velocity vector fields of inner gas flow were measured by a time-resolved particle image velocimetry (PIV) method. The transient behavior of liquid film when after of soap bubble ruptured was captured using a high-speed camera with 3600 frames per second. After rupturing of soap bubble, the inner gas flow out to the outside through the hole of crack. This is called the primary flow. The primary flow was generated by the pressure difference between the inside and outside of the soap bubble. The removal velocity of upper liquid film was faster than that of bottom liquid film since upper side of film is thinner due to gravity. The vortex was generated at the upper boundary and bottom boundary of liquid film. It is found that a series of the Kelvin-Helmholtz vortices, which arise in shear flow along a contact discontinuity, are formed around the bubble sphere. The primary flow moves continuously toward the direction of the rupture point. The secondary flow was generated due to momentum change after impinging soap film into a point, and it was faster than the primary flow. The jet-like secondary flow moves perpendicular to the impingement position and penetrates inner gas volume abruptly. Fire extinguishing experiment was performed by using a nitrogen gas filled soap bubble. It is confirmed that the combined flows of nitrogen gas extinguished the candle fire completely.

Soap Bubble, Particle Image Velocimetry(PIV), Fire Extinguishment, Liquid Film, High Speed Camera

For more than a decade, energy harvesting devices have been rapidly developed based on the electrical energy conversion techniques from kinetic energy using piezoelectric, electrostatic, and electromagnetic principles. However, the amount of power is insufficient for practical products. Recently, a new concept of energy harvesting, the reverse-electrowetting technology has been invented. This method demonstrates that an oscillating water bridge between two parallel conducting plates can generate an AC electric power. The electrical double layer capacitors formed on the two interfacial areas of a water bridge and plates are continuously charged and discharged when the shape of the bridge is mechanically modulated with vibration. In this study, we observe and analyze the dynamic behaviors of a liquid bridge between two plates while the bottom plate is oscillating. For this research, we treat surfaces of each plate hydrophilic and hydrophobic, give variety to vibration frequency and amplitude. Through the images of liquid bridge taken by a high speed camera, the size of contact area and contact angle is measured and flow field is observed by micro-PIV then we find a correlation with output voltage signal. This observation could contribute to more accurate prediction of the behaviors of oscillating droplets and development of micro fluidic power generation devices.

droplet, reverse-electrowetting, liquid bridge, surface treatment

A study was undertaken to understand the flow physics produced by two slender bodies in close proximity in high-speed airflow. The interference flowfield generated by the bodies is dominated by shock and expansion waves, and of particular relevance is the complex interaction of the three-dimensional (3D), curved bow-shock wave emanating from the generator body, striking the cylindrical surface of the receiver body – the principal body of interest. The disturbance shock wave alters the surface pressure distribution and the local flow angularity over the receiving body, effectively modifying its overall aerodynamic characteristics. To gain insight into the shock wave-body interaction, an oil-film surface-flow visualisation technique was employed.
Initially, a heavy oil carrier fluid, combined with a monochrome pigment was used, but the wet pattern was ruined during shutdown of the supersonic blowdown facility. In addition, a thick oil ridge formed along the 3D separation lines, which were found to be intrusive to the near-surface flow. Consequently, the carrier fluid was substituted for a more volatile substance (kerosene), which evaporated within the duration of the blowdown. The traditional monochrome pigment was also exchanged for powdered colour paints, whose particles were finer than the initial titanium-dioxide pigment, in order to further reduce the intrusiveness of the mixture. The kerosene-paint combination was mixed with a volumetric ratio of 2:1, and various colours were applied to the test-pieces at different locations.
The mixture left a dried coat of fine powder streaks on the surface, which could be imaged after tests were concluded, providing insight into phenomenological aspects of the interaction. Matte-acetate tape was then pressed onto the surface, lifting the pattern off the test-piece, and then pasted onto paper, conserving the undistorted full-scale pattern. Together with datum markings along the sting, this procedure allowed the shock impingement location to be quantitatively extracted at various meridian angles around the model, providing validation for the numerical data generated for the same configuration. The computational results were then used to characterise various 3D aspects of the interaction, which are complex to investigate experimentally.
Not only did the extension of the standard surface-flow visualisation method produce attractive experimental images, the high contrast of the multiple colours also allowed the fine streaks to be tracked back towards their separation and re-attachment lines. Moreover, the finer particles produced crisp separation lines on the body’s surface in comparison to other traditional techniques, confirming the advantage of the current method.

colour surface-flow visualisation, slender body, shock wave

In this letter, we report on the 3D-PIV system using Plenoptic lens at micro scale field. The 3D-PIV system measured at micro scale field is required. DHPIV and Micro PIV are well known as measurement method of three-dimensional velocity field of micro scale. However, it’s difficult to increase particle density at DHPIV due to characteristic of hologram. And Micro PIV doesn’t have enough precision in depth.
Recently, the old concept of the light field camera, which records three-dimensional field, was demonstrated using Plenoptic optics. The Plenoptic optical system was soon applied to PIV system.
The objective is to apply the Plenoptic optical system to microscopic PIV, to measure three-dimensional velocity field in micro scale flow.
To achieve this objective, at first, we try to design each parameter of microscopic PIV using Plenoptic lens. Each parameter are distance between object, object lens, main convex lens, micro lens array and CCD camera.
Each parameter are decided utilizing condition that to don’t overlap beside sub-images and each sub-image is smaller than micro lens’s size. As the result, we could obtain sets of sub-images which have parallax using designed parameters.
Next, we calibrate parallax and depth to verify possibility of realization of microscopic PIV utilizing above optical system. We used micro scale as object. Then it was moved it every +10µm for depth direction and displacement of parallax was examined. We reconstructed images which are recorded in each depth using various parallax values. As the result of images reconstruction, every parallax is changing 2 pixels in every +10µm for depth direction.
Finally, we tried to apply calibration result using micro scale as object to the visualization of micro scale flow. We recorded nylon particles, 1µm in diameter, seeded in the micro scale flow field with 100µm square in cross section. Then images were reconstructed utilizing above calibration result. We confirm existence of particles in each depth at same time and examine the depth location of focused particles. Next, we try to three-dimensional analyze of particles location. As the result, we could decide particle depth and show three-dimensional graph of particle location. However, three-dimensional graph is including measurement error such as that particle images are not succession.
In conclusion, we designed Plenoptic optical system in micro scale field, and calibrated relationship of depth and parallax. Using designed sysyem three-dimensional particles location was effectively analyzed. It shows feasibility of microscopic PIV using Plenoptic optical system.

PIV , Plenoptic lens

The flow generated by the rotation of the finite disk in a stationary cylindrical casing is investigated by the three-dimensional numerical simulation and the flow visualization. The complex flow structures depending on geometric and kinematic parameters occur in these rotor-stator cavities. The objective of this study is to clarify the influence of the dimension of the radial gap between the rotating disk and the cylindrical casing on the flow structures. Three disks with different radii are used. The numerical simulation is carried out at several Reynolds numbers based on the disk radius and the azimuthal velocity at the disk rim. The flow is at rest in the initial state and then the disk is rotated rapidly to reach specified Reynolds numbers. The governing equations are the three-dimensional unsteady incompressible Navier-Stokes equations and the equation of continuity. The transition of flow modes with Reynolds numbers is confirmed by the flow visualization on each disk radii. The results of the visualization based on the Q criterion show that Taylor vortices and spiral vortices appear in the radial and the axial gap, respectively. In the radial gap, the Taylor vortex flow transitions to the wavy Taylor vortex flow and further to the turbulent Taylor vortex flow with the increment of the Reynolds number. The width between the disk and the casing has the influence on the number of Taylor vortices and their organized structure. When the radial gap is wide, the Taylor vortex flow is more unstable than the narrower gap flow. In the axial gap, small spiral vortices which have negative front angles to the azimuthal rotating direction arise along the disk rim when the state of Taylor vortices becomes wavy Taylor vortices. Spiral vortices become larger and front angles of vortices turn to positive angle at high Reynolds numbers which are close to the critical numbers of the cross-flow instability on the rotating disk flow. The time variations of the energy of the flow and the torque acting on the disk are estimated from the computation results. Depending on flow states, the energy and the torque show converged values, oscillated values with small amplitude and chaotic values. These results indicate that there is a possibility to control the energy loss by the flow resistance in such systems by selecting the suitable flow modes.

rotating flow, vortex structure, rotating disk, numerical simulation

A fast response pressure-sensitive dot array sensor for unsteady flow measurements has been developed by means of an inkjet printing device on an anodized aluminum (AA) substrate, which has been used for unsteady flow measurements. A bi-luminophore AA-PSP is demanded for precise pressure measurements, because PSP needs the temperature correction. However, a conventional bi-luminophore AA-PSP prepared by a dipping method does not work well due to the interference between the two luminophores. To overcome this problem, we have been developing the isolated dot arrays of PSP and TSP formed on an anodized aluminum substrate by an inkjet printing method. As the first step of realizing the combined AA-PSP TSP, we fabricated a pressure-sensitive dot array sensor on an anodized aluminum substrate using Ru(dpp)3 as a pressure-sensitive luminophore. Ru(dpp)3 was dissolved in four different solvents: methanol, dichloromethane, chloroform and the mixed solvent of dichloromethane and chloroform, and the effect of the solvents on PSP dots was investigated.
The formed PSP dots exhibited significantly different properties, such as the luminescence intensity distribution and pressure sensitivity, depending on the solvents. The PSP solution with methanol resulted in the O-shaped stain of luminophore due to the “coffee-ring effect”. The PSP solution with dichloromethane and that with the mixed solvent of dichloromethane and chloroform formed dots with uniform luminescence intensity distribution. In addition, the PSP with dichloromethane or dichloromethane + chloroform had comparable pressure sensitivity with conventional AA-PSP prepared by a dipping method, while the PSP with methanol showed very poor pressure sensitivity. The developed bi-luminophore AA-PSP was compared with a conventional AA-PSP prepared by a dipping method.

Bi-luminophore Pressure-Sensitive Paint, Inkjet Technology, Dot-Array Sensor, Coffee-Ring Effect,

After the occurrence of a large-scale disaster, such as the Great East Japan Earthquake, multiple simultaneous fires often break out, and also infrastructure, such as water utilization for firefighting, roads and so on, is violently destroyed by the disaster impact. As a result, it is difficult to use conventional firefighting methods against the post-disaster fires. On the other hand, the fire extinguishing method with a blast wave produced by an explosion is very powerful and has some advantages. First, the blast extinguishment method can blow out a large oil well fire in short duration. Second, the effective area of the blast wave to fire extinguishment can be controlled by the amount of input energy to the explosion. Based on the consideration, the authors propose to use the blast extinguishment as the emergency firefighting technique and the damage mitigation measure of the post-disaster fire. However, the blowout mechanism of the blast extinguishment has not been clear yet. In our previous study, the flame extinguishing experiment by using a 10 mg explosive charge was performed. As a result, it was found that the vortex pair was generated in the flame zone due to the Richtmyer-Meshkov instability which is caused by the misalignment of local pressure and density gradients. The vortical fluid motion caused local extinction, and the flow of the combustion gas produced from the explosion interacted with the flame. And then, the flame was completely extinguished. From the experimental results, it is considered that the Richtmyer-Meshkov instability is the key factor to extinguishing a diffusion flame with a blast wave. However, it is not easy to discriminate the extinguishing effects of the blast wave and the combustion gas flow of the explosion on the diffusion flame. In the present study, in order to clarify the blowout mechanism of the blast extinguishment, the blowout experiments of a diffusion flame have been performed with a blast wave produced by laser-induced air breakdown, and the blowout processes have been visualized by using schlieren technique. The distance between the breakdown point and the flame base position is varied as an experimental parameter. This paper will discuss about the blowout mechanism of the blast extinguishment in detail.

Blastwave, Diffusion flame, Laser-induced breakdown, Extinguishment

Impingement jets are often used for cooling and heating of a surface or a body, where a high heat transfer coefficient is obtained near the stagnation point of impinging jet flow. Such impinging flow devices allow for short flow paths and relatively high rates of cooling from comparatively small surface area. Heat transfer and flow characteristics of one and double rows of air jets, which impinge on the heated impingement plate, were investigated experimentally. Experiments with the single jet were also carried out. The jet holes with the diameters D of 1 and 2mm were used in the orifice plate (emitter plate). The distance between the jet-to-jet spacing L in the orifice plate varied between L/D of 4 and 12. And the distance between the impingement plate and the jet exits H varied between H/D of 1 to 10. The experiments were performed with the relatively low Reynolds number Re (based on the jet exit velocity) of 250~1600. The surface temperatures over the impingement plate were measured using an infrared camera, from which heat transfer coefficients on the surface were calculated. The behavior of the flow containing small tracer particles was visualized by means of a Laser Light Sheet (LLS) and a high speed camera.
It was found that heat transfer coefficients are larger in the order of double rows of jets, one row of jets and a single jet. It was also found that the averaged and stagnation Nusselt numbers become larger, when L/D is smaller, and Re and D are larger. Additionally, within the parameter range of the experiments, a non-dimensional correlation between Nuave. and ReG, which does not vary much with H/D, L/D and D, was obtained, where Nuave. is the averaged Nusselt number and ReG is the Reynolds number based on the mass flow rate.　The flow behavior of one and double rows of jets before and after impingement was observed. The flow after impingement was observed to move into the direction perpendicular to the line of jet holes and the stagnation points were observed on the impingement plate. The secondary stagnation points were also observed on the impingement plate for the double rows of jets.

Inpingiment Jets, Heat Transfer, One Row of Jets, Double Rows of Jets, Jet Hole Diamater

Okinawa is located in the southern area in Japan and is subtropical islands enclosed in the ocean. There, therefore, is a problem that corrosion of the structures progresses quickly because of high temperature and humidity and adhesion of sea-water mist flying from sea. For instance, since the Benoki Bridge located in Kunigami village, Okinawa, was built in 1981, it is broken by remarkable corrosions in July, 2009.

The authors are interested in the relationship between corrosion of sea-water mist and flow structure. Authors, therefore, attempt two approaches. One is to understand to flow structures inside bridge beams, another is collision of sea-water mists to beams walls.

Authors make a 1/15 scale bridge model to investigate the flow around the bridge beams and the model is made by the transparency acrylic resin to visualize inside flow. The bridge beams are consisted of two cavity structures. The beam model has 0.1m in height (H), 0.4m in width (W) and 0.15m in each cavity width (W1 and W2). And also the distance L from bridge beams to water surface is varied at that L/H =0.5, 1, 2. Velocity U is set at 5m/s and the Reynolds number is about 5.0x104. The inside flow images are captured by high-speed camera (Phantom V710, 6000fps, 1280x800pixels). The flow is illuminated by CW Nd:YAG (8W, 532nm) as laser sheet light with 1mm width. Time-series velocity vectors are obtained by recursive direct cross-correlation method. As the results, authors confirmed two flow structures by varying distance L from bridge beams to water surface

Next, authors attempt the numerical approach to understand the collision of sea-water mists. Here, a whole field flow is used by velocity data obtained by PIV. These behaviors of sea-water mists are given by equation of translate motion of particle (droplet). Frequency of collision of droplet is investigated in side walls. From the results, authors are made clear that frequency of collision are too much near stagnation point of wall.

Flow visualization, PIV, Motion of droplet

Numerical research of supersonic flow around an aerodynamic configuration having a tail part in the form of a truncated cone was carried out. Analysis of numerical visualization of flow fields and distributions of the gas-dynamic parameters was performed. The calculated results and the experimental data are compared. Characteristics of the supersonic flow associated with the drag of an aerodynamic configuration with a stabilizing element in the form of a truncated cone are considered. Particular attention is paid to elucidating the features of the pressure distribution on the conical tail part.
The performed numerical investigations of the aerodynamic configuration with a conical stabilizer (flare) have shown that the value of the pressure on the surface of the aft section highly depends on the nose shape of a flying vehicle [1]. Behind the bow shock attached to the nose we have a high increase of gas pressure, a decrease of the local Mach number and an increase in entropy. The conical nose part with a small aspect ratio causes a more considerable entropy change and results in a more emphatic display of the nonmonotonic character of the flare pressure distribution.
A numerical investigation of supersonic flow around aerodynamic configurations with a tail part in the form of a truncated cone is carried out depending on the truncated cone semiapex angle. The results of numerical simulation and the experimental data [2] of flow around the cone – cylinder – tapering part configuration also indicate the nonmonotonic character of the aft section pressure distribution. The results of the numerical investigations prove that the features of the pressure distribution on the conical tail part are not associated with the shape of its surface in any way.
The performed numerical visualization of space flow fields made it possible to establish the key influence of the bow shock wave and the expansion flow interaction on the pressure distribution on the surface of the conical tail part.

Acknowledgements. The work was supported by the Russian Foundation for Basic Research (grant No. 13- 01-00854а).

References
1. Kravtsov, A. N. et al. Numerical Visualization of Flow around a Supersonic Flying Vehicle with a Conical Stabilizer. Journal of Flow Visualization & Image Processing. 2012, 19(2), 113–120.
2. Martynov A.K. Applied Aerodynamics. Mashinostroenie, Moscow, 1972

Main subjects: flow visualization Fluid: high speed flows, flows with shocks Visualization method(s): numerical visualization Other keywords: axisymmetric flow, conical stabilizer (flare), flare semiapex angle

Recently, the study about supersonic microflow has become important due to increase in engineering applications such as propulsion, power generation, cooling of MEMS component, laser machining, flow control, and so on. In order to improve the performance of a supersonic flow created by a micronozzle, the detailed characteristics of this flow should be understood.
A lot of computational studies about supersonic micronozzle flows were conducted because it is difficult to measure these flows. However, the computational results in these studies were not satisfactorily validated; i.e., the results were not validated by detailed experimental data such as velocity profiles because such data have never measured. In the present study, we measure the velocity profiles just downstream of the nozzle exit with a high spatial resolution using molecular tagging velocimetry. The simulation results are validated by the measured velocity profiles and the flow inside the nozzle is discussed in detail.
The micronozzle is designed using the method of characteristics so that the Mach number at the nozzle exit is 2.0 assuming inviscid flow. The nozzle heights at the throat and exit are 286 μm and 500 μm, respectively. The nozzle width is 5000μm. The velocity profile is measured at the location 500 μm downstream of the nozzle exit with a spatial resolution of ~10 μm using acetone-based molecular tagging velocimetry.
In the numerical simulation, the governing equations are two-dimensional Reynolds averaged Navier-Stokes equations. The k-ω two-equation turbulence model is employed to estimate the eddy viscosity. The inviscid flux is estimated by using the flux difference splitting method. In this estimation, the physical values on the left and right sides of the cell boundary are calculated by using the scheme that satisfies a total variation diminishing condition and has fourth-order accuracy in space. The viscous flux is determined by a second-order difference scheme. The time-integration is performed by the three-stage Runge-Kutta method.
The computational velocity profile agrees well with the measured profile for each flow condition; i.e., the computational results are validated. The flow characteristics in the present micronozzle are remarkably different from those observed in a macronozzle. It is surprising that a streamwise pressure distribution has a peak inside the nozzle although the flow is underexpanded. This peak moves upstream with decrease in Reynolds number; i.e., the features peculiar to supersonic micronozzle flows are successfully observed.

supersonic micronozzle, microflow, numerical simulation, molecular tagging velocimetry

Boiling heat transfer is dominated by sensible heat transfer due to bubble agitation in low heat flux and latent heat transfer due to microlayer evaporation in high heat flux. Kim et al. (2009) reported that heat transfer through the microlayer evaporation and contact line heat transfer do not contribute more than approximately 25% of the overall heat transfer in the isolated bubble region. Therefore, evaluating convective heat transfer due to bubble motion is essential to understand boiling heat transfer especially in low heat flux. However, randomly emerging bubbles and their coalescence prevent us from observing flow structure near a heat transfer surface. To visualize flow structure near a heat transfer surface, we constructed a quasi-two-dimensional space called a Hele-Shaw cell. It facilitates the observation of bubbles and the heat transfer surface by confining growing bubbles to the cell. This paper reports visualization of flow structure around nucleate boiling bubbles in a Hele-Shaw cell using particle image velocimetry.
Test fluid is pure water with fluorescent particle dyed by rhodamine B. We generated nucleate boiling bubbles on a SUS304 foil in a Hele-Shaw cell by electric heating of the foil. Particle images were taken by high speed camera with a long pass filter to eliminate green laser light (532nm) reflected by boiling bubble surface.
Boiling curve almost agreed with the nucleate boiling correlation by Nishikawa et al. This result is consistent with the results of Nishio et al. (1997) indicating that there is no difference between the heat transfer characteristic of three-dimensional space and that in quasi-two-dimensional space. In low heat flux, liquid near the heat transfer surface is pushed aside by growing bubbles on the surface. Then, we observed vortices under rising bubbles. These results support a model that superheated liquid layer on the heat transfer surface is pushed aside by growing bubbles on the heat transfer surface and superheated liquid is replaced with cold liquid above superheated liquid layer by rising bubbles. On the other hand, there is little water on the heat transfer surface under high heat flux condition. This suggests that latent heat transfer by microlayer evaporation mainly occurred compared with sensible heat transfer. By visualizing the flow structure around the bubbles in a quasi-two-dimensional space, we confirmed the relation between flow around the bubbles and the heat transfer.

Boiling heat transfer, Particle image velocimetry, Hele-Shaw cell, Heat transfer mechanisms, Convective heat transfer

Boiling heat transfer in microchannels has wide applications such as compact heat exchangers and electronics cooling devices. However, pressure increase by plugging up of narrow channels with boiling bubbles is a key issue to utilize boiling heat transfer in microchannels. Earlier studies have found that pressure loss through microchannels and its fluctuation dramatically increase with an increase of heat flux when boiling bubbles emerge. Relations among heat flux, pressure loss, and boiling bubble behavior, indicate that variation of pressure loss are highly related to boiling bubble behavior. However, few studies have focused on quantitative relation between temporal boiling bubble behavior and pressure loss fluctuation. Additionally, few studies have focused on response times of pressure sensors during pressure loss measurement through microchannels, though the inner volume of the microchannels is comparable to that of the pressure sensors. Therefore, the objectives of this study are to find relation between boiling bubble behavior and temporal variation of pressure loss in a microchannel and to evaluate response time of pressure sensors.
We employed transparent plastic for our microchannel material to observe boiling bubble behavior. We generated boiling bubbles using electric heating of a metallic foil in microchannel. We employ several kinds of connecting tubes with different hydraulic diameter and length to find effect of the tube on the response time of pressure sensor. Recording of boiling bubble behavior by a high speed camera was synchronized with the pressure loss measurement through the microchannel. Boiling bubble flow behavior such as size and positions of boiling bubbles, transition speeds of the slug bubble, and void fraction of the microchannel are estimated by image analysis.
At low heat flux, pressure loss increased as boiling bubble’s diameters and their population density, number of bubbles on the surface, increased. We observed boiling bubbles sticking to the microchannel surface and small fluctuation of pressure loss. At high heat flux, we observed the relation between length of slug bubble and fluctuation of pressure loss, while we also observed the relation between transition speed of the slug bubble and dramatically rise of pressure loss. The response time of the pressure measurement became short when hydraulic diameter of connecting tubes from the microchannel to pressure sensors is as large as or larger than the microchannel’s diameter.
We found quantitative correlation between boiling slug length and pressure loss by observing bubble behavior and by measuring temporal pressure loss simultaneously.

microchannel, narrow rectangular channel, bubble behavior, flow boiling, pressure loss, pressure fluctuation

The unsteady flow field in a transonic diffuser has attracted a great deal of interest not only because of the practical industrial importance but also because of the complexity of the flow itself. It is well known that a shock wave in a transonic flow is basically unsteady due to the interaction between a shock wave and other flow phenomena.
The approach to stabilize the unsteady flow fields is divided into two major controls, which are active control, i.e., with jets and passive control, i.e., with a porous cavity or vortex generators. These controls are expected to generate the opposite phase of signals or to retard separations of boundary layers. However the causes of the oscillations include pressure disturbances in a core flow and unsteady phenomena associated with the shock-boundary layer interaction, as mentioned above, the future trend for the oscillation controls might be a combination of passive and active controls.
This work considers control of the shock wave and unsteady flow field to use piezeceramic actuator at the diffuser throat. Experimental and numerical studies of the response of a bimorph type piezoceramic actuator set at the throat to a transonic diffuser is carried out by visualizing the flow field using schlieren technique and measuring wall static pressure fluctuation. We also adopt the template matching technique with cross correlation for capturing time series variation of the shock wave position. The diffuser used in this experiment is circular arc half nozzle with the height h* and width w of 3mm and 27mm, respectively. The blockage factor of the piezoceramic actuator to the diffuser throat is 9.2%. The piezoceramic actuator is attached at the throat of the diffuser and driven by sinusoidal amplified voltage signals.
It is found that the wall static pressure fluctuations and the behavior of the shock wave are clearly affected by the vibration of the piezoceramic actuator. The pressure fluctuations at the downstream of the throat and shock wave by schlieren image correspond to the exact the same frequencies of the input frequencies to the piezoceramic actuator for all driving frequency. This results mentioned above suggest that the driving the piezoceramic actuator at the diffuser throat can be one of the promising techniques to control unsteady transonic diffuser flow.

transonic flow, piezoceramic actuaotr, shock wave

It is known that the two-dimensionality of the flow may be significant for the accurate estimation of the aerodynamics of various two-dimensional bluff bodies, but it is very difficult to secure the two-dimensional flow field. Recently, it has been indicated that the suction pressure coefficient increases locally in the end region of a circular cylinder supported by the end walls on which the transitional boundary layer forms. In addition, this effect is remarkable for the circular cylinder with the smaller aspect ratio than with the larger aspect ratio. This effect is considered to occur due to the secondary flows behind the circular cylinder, but the cause why secondary flow occurs still has not been found.
Therefore, in this paper the secondary flow structure in the near wake behind a circular cylinder making junction with end wall have been investigated by measuring the base pressure and by using the moving visualization and PIV method. The relative boundary layer thickness δ/d, defined as the ratio of the laminar boundary layer thickness δ against the circular cylinder diameter d, is varied from 0.26 to 0.82. The measurement of the base pressure is carried out in the wind tunnel testing at the Reynolds number of Re=U∞･d/ν=3000 or 6000, where U∞ is the velocity of uniform flow, and the moving visualization is carried out in the water channel testing at Re=1000.
When the laminar boundary layer on the end wall is relatively thick, the base pressure coefficient varies greatly in the cylinder end region up to three diameters distance, but it is constant excepting the end region. On the other hand, the recirculation region in which the streamwise velocity U is negative becomes extremely narrow in the end region. The narrow recirculation region probably causes the increases of the base suction coefficient.When the laminar boundary layer is relatively thick, the base pressure coefficient almost does not vary over span on the cylinder, and then, it slightly rises in the end region. In addition, the effect of aspect ratio on the base pressure coefficient is smaller than in the case of thick boundary layer.

Aerodynamics, Cylinder wake, Junction flow, Moving visualization, Base pressure

In recent years, application of microbubbles has been studying in various fields. For instance in biomedical engineering the use of microbubbles for enhancing the effect of ultrasound treatment on cancer has been studying. On the other hand, in maritime engineering Abe et al. are going to apply the shock waves generated by collapse of microbubble to ship’s ballast water treatment. However, it is difficult to measure and observe the microbubble behavior because microbubble dimension is extremely small. Therefore the detailed dynamic properties of microbubbles have not been clear yet.

Generally, when bubbles are exposed to shock pressure, high pressure and high temperature are generated inside them. If the initial bubble diameters are so small such as a microbubble, propagation speed of a shock wave passing through a microbubble becomes relatively faster. Hence, it is thought that microbubble could be exposed to the pressure behind shock wave instantly. We could expect that the microbubbles contract and expand ideally and spherically, then the pressure and temperature inside microbubbles become extremely high and they produce shock wave around them.

This paper reports on observation and analysis of microbubble motion induced by an underwater shock wave. In the experiment, microbubbles were produced using air trapped in salt crystals. Underwater shock waves that induced microbubble motion were generated by electric discharge. A high-speed camera and an ultra-high-speed framing camera were used for observation. In order to improve the observation accuracy, we proposed a spatial position control method of the microbubbles. We tried to take shadowgraphs in the viewing width of a few millimeters. In the analysis, a one-dimensional spherical and symmetrical model based on Herring’s bubble equation was solved numerically using an experimental pressure profile of a shock wave.

As a result of the experiments, we obtained shadowgraph of microbubbles collapse and a rebound shock wave generation. In addition, regarding time variation of the bubble diameters, the numerical analysis results showed good agreement with the experimental results when microbubble motion is spherical. Because microbubble diameter is so small that surface tension becomes strong, the motion of a microbubble interacted with a shock wave is probably close to the ideal solution for a one-dimensional theoretical model of the single-bubble motion equation. Besides in the experiment that the multiple microbubbles are exposed to shock wave, we observed increase of the bubble diameter and decrease of the number density of bubbles with combination of the microbubbles.

microbubble, bubble collapse, rebound shock wave, shadowgraph

The interaction between vortex and wall is one of the hot topics in the fluid mechanics. Recently, the development of synthetic jet has made the vortex ring continuously impinging onto the wall become possible. However, most of the studies focused on the influence of Reynolds number, seldom paid attention to the influence of stroke length. So the influence of the stroke length on the process of synthetic jet vortex ring impinging onto the wall was studied using LIF and Two-dimensional PIV in our study. The experiment was conducted in a well-designed tank with size 600×600×600mm. The tank was made of plexiglass guaranteeing a good transmittance. In the experiment, the orifice-to-wall distance was fixed as H=4D (D is the orifice diameter) and the synthetic jet Reynolds number remained the same as ReU0=152. The synthetic jet vortex ring was generated by a piston-cylinder apparatus which was drove by a high-precision servo motor. A two-dimensional PIV system was employed to measure the flow field illuminated by a continuous laser and the maximum sampling frequency of CCD camera was 200 Hz.
It was found that as the stroke length increased, the radial spreading of the primary vortex ring seemed to decrease, which was concluded from the visualization results. In addition, the range of the wall jet induced by periodic vortex rings impingement was also decreased as the stroke length increased. These could be explained as follow: as the stroke length increased, the circulation of the primary vortex ring also increased so the stronger vortex ring could induced a stronger reverse vorticity in the near-wall region, and then this stronger reverse vorticity conversely hindered the spreading of the primary vortex ring. Furthermore, the statistical characteristics of the PIV measurements were also provided to reveal the mechanism of the flow quantitatively in our study.

Stroke length, Synthetic jet vortex ring, Impinging, Wall

In low Reynolds numbers region’s flow, a laminar separation region and a separation bubble are observed on an airfoil surface, these separation flow contribute to changing aerodynamics of the airfoil. We intended to improve the aerodynamics of a NACA0012 airfoil, therefore, a pulsed DBD plasma actuator is applied on the airfoil surface in order to control and suppress separated flow involving a laminar separation and a separation bubble on the airfoil.
In this study, we visualized the flow field around the NACA0012 airfoil to examine an effect of induced flow by the plasma actuator on the separated flow around the airfoil at 30,000 of Reynolds number. The flow visualization was performed with using smoke-wire method to examine the flow field around the airfoil. Induced velocity by operating the plasma actuator was about 1.5 m/s, the ratio of the induced velocity to uniform velocity is about 50 %. We changed the angle of attack from 1 to 20 deg. The plasma actuator was put in the position of 5 % chord length from leading edge of the airfoil and the actuator was only driven in a pulsed modulation wave mode which varied both of the duty ratio DR and non-dimensional modulation frequency F+.
As the results of flow visualization, flow field involving vortexes which shed from nearby electrode of the plasma actuator simultaneous with modulation frequency fm was observed on the airfoil surface in any visualization cases. When the angle of attack was high region over 13 deg., extensively separation from leading edge was suppressed effectively as well as driven in the steady wave mode, however, a separated flow was changed into reattached flow involving vortexes which different from the reattached flow of the steady wave mode. The angle of attack was middle region from 5 deg. to 13 deg., on the other hands, the shedding vortexes by operating the plasma actuator interfered in both of the laminar separation region and the separation bubble, and it reduced the laminar separation region and the length of the separation bubble. And, the shedding vortexes brought about on the airfoil surface involving vortex street with changing distance between vortexes as varying non-dimensional frequency F+. We would like to examine details of relationship between the aerodynamics and the flow field which affected by the plasma actuator with varying F+ using a quantitative method such as measurements of the aerodynamics and flow field of the airfoil.

plasma actuator, flow control, airfoil, low Reynolds number

Water flooding in oil production process is crucial. Injection of water into oil-wet and water-wet glass beads will sweep oil in pore spaces toward production well. During the process, some oil can be disconnected due to nonhomogenous displacement front of water. Capillary pressure holds this oil in pore space, and it is trapped. Actual oil reservoir also contains connate water; water trapped in the porous of rock during its formation. This connate water also affects the characteristic of water flooding. Three dimensional water flooding can be observed nondestructively by utilizing a microfocused X-ray computed tomography scanner. We developed a visualization method by carefully arranging the brightness distribution of all phases involved in water flooding so that false images that usually appeared due to broadening effect of X-ray can be eliminated. To demonstrate imbibition and drainage processes during water flooding, experiments were conducted using oil-wet and water-wet porous media. Variation was made by adding connate water in packed glass beads. The water phase was injected upward into packed glass beads, and the process was scanned every minute until steady state was reached. Using this scheme, the water invasion pattern and oil trapping process in clusters of pores and individual pores can be observed step by step clearly. The effect of the existence of connate water can also be observed. By eliminating false images, the boundary between oil and water phase can be observed with high precision, even in a single pore. Direct measurement of the pore throat radius and the contact angle between the wetting and nonwetting phases gave an approximation of the capillary pressure acting on particular pores.

Visualization, imbibition, drainage, oil trapping, X-ray CT scanner

As a new experimental technique of aerodynamics, optical flow test technique gradually attracts more and more attention for the advantages of vector field measurement of pixel scale resolution and strong smoothness ability. By means of scalar constraint equation combined with smoothness constraint condition, optical flow test technique can measure global velocity vector field of high space resolution. In this paper, the theory and algorithm of integration minimization optical flow velocimetry were studied, an verification experiment, in which tracer particle images was acquired by high speed camera and velocity vector field was calculated by optical flow algorithm, was completed. The result calculated by optical flow algorithm was compared with result calculated by PIV algorithm, both results were significantly correlated, it shows that optical flow test technique possesses the advantages of space resolution and velocity field smoothness.

optical flow; velcocity measurement; particle image; motion estimation; integration minimization

Present paper describes the correlation between cavitation inside nozzle and progress of atomization in liquid jet flow. The optimization of fuel atomization inside cylinder is vital for increasing thermal efficiency of combustion engines. It is our mission to decreasing the emission of greenhouse gases, and the better efficiency of combustion engines is one of the key issues for the mission. The authors have tackled with present eternity mission, and try to clarify the fundamental mechanism of flow field to obtain an optimum condition. In the previous study, the authors have designed transparent two-dimensional nozzle, and both the flow field of liquid jet flow and the cavitation inside nozzle were visualized. By observing the flow field, the authors have confidence that the location and fluctuation of cavitation may be the key factor on determining the progress of atomization, however, the clarification based on quantitative evidences was not obtained.
In the present paper, the cavitation inside nozzle was evaluated by applying image analysis. The visualized images are obtained by backlight imaging, and the cavitation was recognized as shadows. The numerical information of length, thickness and their fluctuation of cavitation have been obtained simultaneously by image analysis, and it can be utilized to examine the correlation with progress rates of atomization. The sequential analysis was realized by using extra-high-speed video system, and the details of changes of cavitation and atomization was able to be investigated. The authors have already established an evaluation method of atomization in liquid jet flow, and it has been combined with evaluation method of cavitation proposed in this paper. The spatio-temporal change of cavitation in nozzle and progress of atomization were examined and fine correlations between them were found.
It is found that the change of cavitation and progress of atomization were synchronized, and strong correlation between them could exist. The best performance could be obtained by controlling the cavitation, and present aspects could be utilized for the design of nozzle and fuel injection system of internal combustion engines.

Fuel injection, Cavitation, Atomization, Liquid jet flow

Turbulent gas-liquid flows in vertical pipes occur in many industrial flows and have been studied vigorously due to its physical differences from single-phase flows, especially in terms of pseudo-turbulence. Although the global impact of the bubbles on the liquid phase has been understood so far, more detailed investigations of local and global phenomena in gas-liquid interaction, e.g., the differences in the effect of gas void fraction on the liquid-phase turbulence in developing and fully-developed regions, are further necessary. Thus, in the present study, we have established an experimental method to measure the interaction between two phases, based on the particle image velocimetry and shadow image technique. Algorithm for reliable phase separation between gas and liquid (based on the Median, Laplacian of Gaussian, and Sobel filters) also has been tested and applied. By varying the volume void fraction 0.2 – 1%, we measure the flow statistics in both phases simultaneously in a vertical upward turbulent bubbly flow at Re = 5300. As an inlet condition, non-uniformly distributed bubbles are introduced and the measurements are conducted at different streamwise locations of 3D to 39D (D is the diameter of the pipe) from the inlet. We study the instantaneous flow fluctuations and vorticities caused by the rising bubbles and also discuss the modification of time-averaged turbulence statistics including turbulent kinetic energy budget. Because of the shear around the bubbles, turbulent dissipation increases with the void fraction; however the increase of production is more than that of the dissipation due to the large velocity gradient at the wall. In the core region, the small-scale vortices induced by bubbles introduce strong perturbation into the flow. Consequently, we observe the global enhancement of the turbulence intensity and local increase of the Reynolds stress due to the bubbles, which show up in a different manner depending on the distance from the inlet. Also, due to the turbulent mixing, it is shown that the initially asymmetric profiles of mean velocity and turbulence statistics recover their symmetry along the streamwise direction. Finally, we discuss the modification of turbulent energy budgets in relation to the distribution of bubbles.

turbulent bubbly flow, image filter, non-uniform bubble distribution, inlet condition, void fraction, energy budget, mixing

Preliminary experimental results are presented on the application of Particle image velocimetry (PIV) in the film cooling flow on a blunt body under large attack angle of 20° in hypersonic gun tunnel. The main flow Mach number is 8.1, and the total temperature is about 900K. The injection Mach number is 3.2, and the total temperature is 300K. TiO2 nanoparticles are used to track the main flow field. The characters of the flow field with and without cooling film are presented. The film cooling tests focus on the matched flow condition. Gas and carbon dioxide are used as the cooling gas, and the shear layer between main flow and film flow can be visualized. The carbon dioxide test shows that this gas will condense when jetted out of the nozzle, and a turbulent boundary layer of the film flow can be visualized. The schlieren photographs are also presented in addition as a comparison.

PIV; film cooling; hypersonic; schlieren

As a micro water turbine system for small open channels, the passive oscillating wing unit system that create yawing and swaying motion smoothly was developed. Each individual blade has two-dimensional wing shaped blade supported by the slide bearing with high stiffness in order to maintain the robustness against fluid power. And the wings are connected to the flywheel of the main shaft through a crank mechanism with “T” shaped link which can adjust length and attach angle. This mechanism is easy to detach and attach from the base equipment. And it’s also easy to set the phase difference φ between upper wings and lower wings.
In this study, basic performances of this equipment such as rotational fluctuation, output, and turbine efficiency of 2-wing setting and 3-wing setting were measured in a small water tunnel. Tested flow velocity is almost the same as a small agricultural irrigation channel.
As a result of both condition, relatively small rotational fluctuation were shown in the case of φ=90°. And small eccentricity and relatively big output were measured in the case of 3-wing setting with phase difference of 120-degree. The maximum output of this equipment with which 3-wing setting is 0.62W (U=0.5 m/s), and the maximum turbine efficiency is 46.7%. As is well known, turbulent flow affects the thrust on a wing shaped blade.
When the 2nd row wing follows the 1st row wing, that the phase delay between the wings has positive degrees, the rotational speed of the main shaft slowed down compared with the case that the 2nd row wing goes ahead.
In order to confirm the influence of the wake of the upper wings, visualization of the flow field which passes through between wings was performed. The tracer particles made of cellulose powder are illuminated with laser light sheet. The velocity-vector fields between the 1st blade and 2nd blade were obtained by PIV method. As a result, separation bubble region of wings that has interfered in lower wings was visualized.
As shown in above, developed system with low turbine efficiency is not fit as commercial power resources.
However, this system of fish-like passive wings is available to improve student’s interest to natural power sources or their motivation.

Flow visualization, Micro water turbine, Oscillating wing, PIV, Fish tail like movement

The feasibility of digital holographic interferometry using a CW laser @ 532nm and a Photron APX camera is demonstrated in the F4-ONERA hypersonic wind tunnel. This optical technique is used to point out the possible combustion of a small hydrogen jet in the shock layer developed on the model. The optical technique generates in the field under analysis, interference micro-fringes which are used as carrier spatial frequency. The FFT2D processing leads to obtain the field of the optical thickness. If the flow is assumed to be two-dimensional, the map of the refractive index can be estimated. The adjustment of the optical bench is easy to implement and the results obtained with this technique can be used for several interesting comparisons. From the phase difference maps, the holographic images and schlieren images in the x and y directions can be recalculated, which is not possible with a conventional schlieren optical setup. In addition, if the characteristics of the ionized gas are well known, the value of the gas density upstream and in the shock layer can be estimated.

Digital holography ; Hypersonic Flow ; inonized flow

In generally, viscosity of water containing micro-bubbles and contamination becomes higher than one of the ordinary water from theory of Einstein’s effective viscosity. However, frictional drag reduction by injecting micro-bubbles has been reported by many researchers. For example, frictional drag is reduced by injecting bubbles at the bottom of the ship.

In general viscosity measurement, There are capillary type, falling ball type, co-axial cylinder type, and corn-plate type viscometers. Authors get a hint from corn-plate type viscometer and try to basic research in cylinder container injecting the micro-bubbles to reveal the mechanism of frictional drag reduction.

In experimental apparatus, the hollow cylinder is 104mm in diameter. A rotating disk is 100mm in diameter. The disk is set at 25mm in height from cylinder bottom and also the disk is control by motor (30, 60, 120rpm). Tap water is filled with the cylinder container. Micro-bubbles (hydrogen/oxygen bubbles) are generated by electrolysis of water by 2 platinum wires. These wires are pasted at 23 and 25mm from bottom on cylinder wall.

In experiment, authors visualize some water flow cases with/without micro-bubbles to investigate the difference of the flow structures with/without micro-bubbles. In each case, tracer particles are insert to measure liquid velocities. These velocities with/without micro-bubbles were measured by PIV and were compared with the angular velocity with/without micro-bubbles. The mechanism of frictional drag reduction with micro-bubble are discussed.

Micro-bubble, Drag reduction, Flow visualization

We investigated the use of dielectric-barrier-discharge plasma actuators as spread controller of turbulent free jet issuing from rectangular exit. Rectangle nozzle of 75mm×10mm (Aspect ratio 7.5) was used here and two plasma actuators were placed at the long sides of the nozzle exit. Actuator was composed of two electrode copper tapes with 50μm thickness which were connected to an external power supply and a bipolar peak-to-peak voltage of 6kV at frequency f=20kHz was applied to create the glow discharge plasma. Unsteady actuation is performed by the low frequency modulation of the base wave and two actuators were operated in phase and/or in opposite phase. Flow patterns were visualized by the smoke method and high speed camera was used. The jet velocity at the nozzle was set at 5m/s and the velocities in the downstream were measured with an I-type hot wire probe and a constant temperature anemometer.
Characteristic frequency of free jet used here was turned out to be 440Hz from the preliminary experiment, so that modulation frequency was selected to multiple of its frequency and fractional one. In the case of duty ratio 100% which means continuous operation of actuators, it was found that the potential core region of the jet was lengthened and the flow development of the jet was delayed. Similar phenomena were observed by ON-OFF control of the actuator with modulation frequency of twice characteristic frequency. On the other hand, when the modulation frequency was 1/8 of the characteristic one with duty ratio 10%, the jet was found to fork into two branches and spread widely. When the modulation frequency was 1/4 of the characteristic one with duty ratio 10%, leapfrogging and uniting of the vortex rings was observed near the jet nozzle exit and the jet spread widely in the downstream.

Jet, DBD Plasma Actuator, Flow Control, Turbulent Flow

Magnetohydrodynamics (MHD) simulations had become a useful tool in investigation of plasma fluid phenomena. On the order hand, visualization is indispensable in analyzing the simulation results. In general, simulation results are being recorded in the simulation process and will be visualized and analyzed using a scientific visualization software or analysis tool. However, recording data for each time step of the simulation is time consuming. Writing file every step will cause big overhead and slow down the simulation process. In addition, it is storage expensive. Recording data once per several steps is a feasible way but some important snapshots which contained interesting phenomena might be skipped. Therefore, real-time visualization of along the simulation will be significantly helpful.
GPU accelerated implementation speed up the MHD simulation process. MHD simulation and visualization using a single GPU had been proposed in our previous work. However, global MHD simulation requires large amount of memory. Due to the lack of video memory of a single GPU, the scale of the computational domain is limited. Therefore, multi-GPUs are needed for large-scale global MHD simulation. In this paper, a real-time global MHD simulation and visualization system is proposed, utilizing multi-GPUs to enhance efficiency and scale of MHD simulation and private visualization of the data on the fly. Physics quantities of each partition of the calculation domain are not only being evolved but also being visualized in every time step. Our system visualizes each partition using the same GPU that the simulation is running on, and then combines the results for display. Since the visualization is also done within the same GPU where the physics quantities stored, no data gathering is needed. Furthermore, all the GPUs are invoked in the visualization, which performs better load balance. Peer-to-peer GPU Direct Access is used to reduce the overhead when combining the visualization results of each GPU. Thus, mesh models of the ISO surface or direct volume rendering (DVR) images can be generated rapidly. Our experiment results showed 45 FPS (frame per second) and 15 FPS for real-time global MHD simulation and visualization of 180 x 120 x 120 grid-points and 270 x 180 x 180 grid-points, respectively, using 4 GTX-Titan GPUs.

Global MHD simulations, Multiple GPUs, CUDA, Direct Volume Rendering

Experimental studies of supersonic flow over several compression ramps were carried out in a Mach 3.0 wind tunnel with different upstream boundary layers including laminar flow, not fully developed turbulent flow and fully developed turbulent flow. Fine flow structures and velocity field were obtained via NPLS and PIV techniques, typical flow structures such as boundary layer, shear layer, separation shock, reverse flow region and reattachment shock were visible clearly. The results indicated that, when the ramp angles were 25°, a typical flow separation occurred in laminar flow, the boundary layer increased and converted to be turbulence rapidly, which induced a shock in the flow field, hairpin vortices, shear layer and compression waves appeared. While an incipient flow separation occurred in turbulent flow which was not fully developed, the separation region was much smaller, there were no induced shock, hairpin vortex and compression wave in the flow field. What was totally different was that flow separation did not occur in turbulent flow which was fully developed. When the ramp angles were 28°, the laminar flow separated further, the range of reverse flow expanded evidently, flow structures in separation region were very complicated. A typical flow separation occurred in turbulent flow which was not fully developed, there were obvious reverse flow structures in the flow field, a series of compression waves which located at the end of the separation region converged constantly and reattachment shock was formed downstream. By contrast, separation region in turbulent flow which was fully developed was smaller, the boundary layer increased very slowly, there was no induced shock, hairpin vortex and compression wave in the flow field, and flow structures in separation region was relatively simple. The velocity field was corresponding to the flow visualization, with the velocity field structures of the three compression ramp flows conformed to the flow structures. Some significant differences between the three compression ramp flows can be found in the development of boundary layer, the shear layer and the flow separation.

compression ramp, NPLS, upstream boundary layer, fine flow structures, velocity field

This work investigates the reattachment of a turbulent shear layer behind a backward–facing step at Reynolds numbers up to Re = 28 000, based on the step height. The measurements were performed in an open jet wind tunnel at the Bundeswehr University in Munich. With the aim to investigate the interaction of reattaching shear layer vortices with the wall, the dynamic behavior of the near wall vortices must be registered in space and time in order to identify their spatial and temporal behavior. For this, time-resolved particle image velocimetry (PIV) and wall-bounded hot–film sensors (HF) were combined to capture the flow field and the near wall fluctuations, respectively. Where PIV allows for a thorough investigation of the overall flow, the HF sensors provide information directly from the wall. Both systems run simultaneously and record data at high frequencies. The spatial resolution of the instantaneous PIV velocity fields is better than 5% of the step height and the temporal resolution is up to 0.1ms. On the other hand, 32 hot–film sensors, operated at constant temperature, are used to capture date at a recording frequency of up tp 100 kHz. From the PIV data vortices are identified and their motion is analyzed and compared to the HF signals. Thus, the two combined time-resolved measurement techniques reveal fundamental knowledge about the interpretation of the HF signals. This is very important for the analysis of high Reynolds number flows, where time–resolved PIV measurements are often challenging.

PIV, backward-facing step, reattachment, hot-film sensors

A synthetic jet (SJ) is a fluid jet flow which is created from an oscillatory process of suction and blowing during fluid exchange between SJ actuator cavity and its surroundings. A time-mean mass flux through the actuator nozzle is zero, therefore SJ is frequently named as the zero-net-mass-flux jet. A hybrid synthetic jet (HSJ) is a fluid flow produced by the same principle as the SJ. Moreover, incorporating fluidic diodes enhance fluid entrainment from surroundings into the actuator cavity. The rectification effect of the fluidic diodes enhances the volume flux during the pump stroke, therefore the resultant HSJ is basically a non-zero-net-mass-flux jet.
The present experimental study deals with round HSJs issuing into quiescent surroundings. For comparison purposes, experiments with common (zero-net-mass-flux) SJs are performed too. The working fluid is air at the barometric pressure and room temperature. The orifice and fluidic diode diameters are 8 mm and 5 mm, respectively. Flow visualization in air using smoke wire technique demonstrates phase locked flow fields of the HSJs and SJs and the flow fields generating by fluidic diodes. Hot-wire anemometry is used for quantification of the parameters. Moreover, a precision scale is used to measure the time-mean reaction force of the HSJ and SJs relating to the jet momentum. Resonant characteristics of the HSJ and SJ actuators are evaluated by means of three methods: velocity measurements by the hot-wire anemometer, measurement of the actuator impedance, and measurement of the time-mean reaction force of the jets.
The maximum performance of HSJ and SJ was evaluated at actuation frequencies 95 Hz and 75 Hz. The present experiments were made for the Reynolds number Re = 5100 and 4100, respectively. The present results demonstrate advantages of the HSJs in comparison with common SJs, which can be useful for heat transfer applications such as cooling of highly loaded electronic devices.

Flow visualization, Synthetic jet, Hot-wire anemometry

Suspension injection is a crucial point for suspension plasma spray (SPS), an emerging coating process. It must satisfy several requirements such as stability, reproducibility, high yield of suspension particles penetrating the plasma core. Indeed, the particles should follow a proper trajectory inside the plasma in order to be well treated and accelerated. Thus, the quality of the injection has a direct effect on the coating microstructure, therefore on the properties.
This study focuses on the three-step characterization of a twin-fluid atomizer, without and within the plasma. While varying gas or suspension flow rates, the spray was firstly observed thanks to a shadowgraphy system. This system uses a short pulsed diode laser in a back illumination configuration and a robust image processing software, allowing the detection of suspension droplets, even within a high emissive plasma. Secondly, droplet size measurements were performed via laser diffraction. Thirdly, droplet velocities were measured using a Particle Image Velocimetry system.
The combination of the results obtained by these techniques helped us to understand how gas and suspension flow rates impact on droplets size and velocity distributions and finally how one could select the best injection conditions. The injector characterization was completed by coating manufacturing and microstructure analysis.

suspension plasma spray, twin-fluid atomizer, particle image velocimetry

Different types sources of light for use in schlieren systems and shear interferometers are considered. Sources of light include such types as lasers of continuous emission with small coherent length with power up to 5 Wt, light diodes, including special types, incandescent lamps and high-power flash-lamps. Comparative analysis results of utilization such sources for wind-tunnel investigations are presented. Optimal areas of use each type source of light in dependence from solved problems are offered.

shear interferometry, schlieren methods, visualization, sources of light, wind-tunnel experiment

The paper focuses on changes of the characteristics quantities relative to the coherent structures in Turbulent Boundary Layer (TBL) over a drag-reducing riblet plate. To further investigate experimentally the drag reduction mechanism of the riblets, a planar Time-Resolved Particle Image Velocimetry (TRPIV) system at first and then a Tomographic TRPIV (Tomo-TRPIV) system were employed. Time series databases of the two dimensional (2D) instantaneous velocity vectors over the drag-reducing riblet plate and the 3D instantaneous vectors separately obtained by the two TRPIV systems were analyzed accordingly. Newton iterative fitting method was performed on the 2D vector database to portray the mean velocity profile of the TBL over the riblet plate and the one over a smooth plate for reference. The 2D-experiment results with an around 4.8% reduction rate of the skin friction are clearly visible indicating the drag-reducing performance that, over the riblet surface, the buffer layer thickened, the logarithmic-law region uplifted, the turbulence intensities depressed in both streamwise and wall-normal direction and the mean Reynolds shear stress decreased as well. Thus, it seems possible that by lifting the near-wall vortices and keeping them away from the wall, the riblets reduce the momentum and energy exchange eventually the skin fraction in the near-wall region of the TBL. To visualize the vortices, which the characteristics quantities are related to, the 3D velocity vectors were decomposed into different scales with the employment of wavelet transform method based on the concept of multi-scale coherent structures. By comparison of the spatial distributions of each physical quantity, the riblets weakened the amplitudes of most physical quantities when ejection and sweep events occur, and besides more influencing on the sweep events. Meanwhile, the conditional-averaging spatial shapes and the scaling of the coherent structures on a whole in the overlying turbulent flow over riblets were changed, indicating that the bursting events in the TBL weakened, the momentum and energy exchange with outer region of the TBL reduced, then resulting in the drag-reduction.

Turbulent boundary layer,TR PIV,Coherent structure,Drag-reducing riblet,

In studying gas-liquid flows which are very common in various industrial and natural flows, it is very important to characterize the interaction between the rising bubble and the wall toward understanding the physics of gas-liquid flows and assisting numerical modeling. Even though there have been many studies of bubbly flows, there is no clear description about bubble-wall interactions especially in terms of vortical structures between them. Thus, in the present study, we investigate the effect of the wall on the dynamics of a rising bubble by varying (i) the distance between the bubble and the wall and (ii) the surface condition of the wall with high-speed imaging and two-phase particle image velocimetry (PIV). Experiments are conducted for single rising air bubble whose equivalent diameter is about 3.2 mm in a rectangular water tank filled with quiescent water. The Reynolds number and Weber number is as high as about 800 and 3.8, respectively. For the wall, we consider acrylic, Teflon, and sponge which refer to no-slip, slip and permeable boundary conditions, respectively. We also consider sanded (roughened) Teflon which represents larger slip condition. Depending on the wall characteristics, the rising bubble shows quite different behaviors (e.g., sliding, bouncing, and departing) and associated dynamics such as bubble trajectories, mean rising velocity and bouncing amplitude is measured with high-speed imaging technique and the detailed flow structures around the bubble with two-phase PIV. With the walls with slip boundary condition, bubble slides along the wall while being attached to it and the rising velocity is slower than other cases. On the contrary, the bubbles near permeable wall show bouncing motion with larger amplitude than other cases. Also the bubble-wall distance strongly affects the rising bubble dynamics. Except the sanded Teflon, bubbles which are far from the wall (without touching the wall) show both zigzag and rectilinear motions depending on the bubble-wall distance. But in case of the sanded Teflon, bubbles show only zigzag motions when the bubbles are far away from the wall. We suspect that the different bubble behavior originates from the trade-off between the lift, drag, wall lubrication and deformation forces (or energies) during the impact and the detailed bubble dynamics supported by velocity measurements around the bubble near the wall are to be discussed.

bubble-wall interaction, two-phase PIV, bouncing, sliding, wall boundary condition

Electrical capacitance tomography provides the opportunity to visualize the contents of a process of many applications such as pipeline and obtain information on the flow configuration .Multiphase flow is an extremely complex field of fluid mechanics, the characteristics of the operations of many equipment in different areas of industry such asoil and power generation are determined by the nature of flow of two phase or multiphase .In this study , a twin plane Electrical capacitance tomography (ECT)electrodes was designed, fabricated and used to image and characterize oil/gas flow in 67 mm pipe. The experiments were carried out in inclinable facility in Department of Chemical Engineering in Nottingham university, UK.Conditions used are Gas superficial velocities of 0.05 to 5.52 m/s and liquid superficial velocities of 0 to 0.54 m/s.The cross-section averaged void fraction and its variation in time were measured using electrical capacitance tomography. Also, Probability Density Functions are demonstrated and the structure velocity of flow is presented as well. In this project, Bubbly, slug, and churnflow configuration was observed. In addition, high speed video images of flow were obtained simultaneouslyand compared with tomographic images of the ECT system.

Electrical Capacitance Tomography, Gas/Liquid, Vertical, Void Fraction

Synthetic jets (SJs) have been regarded as an effective means for active flow separation control. A typical synthetic jet actuator (SJA) consists of a cavity with an oscillatory diaphragm on one side and an orifice on another. Oscillation of the diaphragm generates a succession of vortex rings that propagates away from the orifice, forming a SJ. In the current experimental study, the interaction between two circular synthetic jets in a laminar boundary layer is investigated. The experimental setup was designed in such a way that the velocity, frequency, and phase of each SJ can be tuned independently, the distance between the SJs can be changed, and the yaw angle between the line connecting of the two SJA orifices and the freestream direction can be varied. The experiments were conducted in a low-speed water tunnel. The momentum-thickness based Reynolds number near the SJ orifice exits was fixed at around Reθ = 180. Both dye visualization and PIV measurements were conducted to obtain the resultant flow structures and velocity fields. Dye visualization results show that at different jet-to-freestream velocity ratios and SJ stroke lengths, different types of flow structures are produced, including hairpin vortices, stretched vortex rings, and tilted vortex rings. For a in-line-with-flow twin SJ configuration, the vortices produced at the same flow and actuator operating conditions could be merged together, partially interacted, or separated completely, depending on the twin SJ phase difference. The effects of these resulting vortex structures on the attached and separated boundary layer were also compared. This study will help achieve more physical insights not only in the interaction between twin SJs in boundary layers, but also in how the interaction delays flow separation.

Twin synthetic jets; Laminar boundary layer; Dye visualization; PIV

In the present study, the flow separation control on a NACA 0025 airfoil using an array of 2D slot synthetic jet actuators (SJAs) is investigated in a low speed wind tunnel through particle image velocimetry (PIV) measurements and proper orthogonal decomposition (POD) analysis. Eleven identical SJAs were designed and deployed at 30% of the chord from the leading edge. Each SJA comprises of two vertically arranged piezoelectric diaphragms with a gap of 8 mm in between and a 12 mm × 0.5 mm slot. Oscillation of the diaphragms at their optimal frequency of 800 Hz under an excitation voltage of 200 Vp produces a synthetic jet (SJ) of peak velocity, 12 m/s. This indicates that the SJA array is able to produce a high momentum coefficient of Cμ = 9.9×10^-4 at the chord Reynolds number of Re = 1.5×10^5. Preliminary hot-wire measurements revealed that, at this Reynolds number, the initially separated flow at the 18° angle of attack reattaches to the airfoil after actuating the SJA array. The detailed flow fields over the suction surface of the airfoil were measured using a time-resolved PIV system at different flow and SJA operating conditions, with and without the actuation of the SJA array. The POD analysis was employed to investigate the impact of the SJs on the dominant features and coherent structures of the separated flows. This study will help improve the understanding of the flow physics of the SJ-based flow separation control mechanism.

Synthetic jets; Flow separation control; PIV; POD

Concerning the thermal contact resistance between contacting solids with flat rough surface, lots of experimental and theoretical studies have been done on the microscopic thermal constriction resistance caused by surface roughness, which is a measure of the additional temperature drop at the contact interface. So far, almost all of theoretical analyses have been performed based on the two-dimensional cylindrical coordinates system, and fairly complicated analytical solutions have been obtained. However, as long as the authors know, it seems that the heat flow behaviors through such contacting solids have not been visualized yet.

On the other hand, the additional thermal resistance associated with the macroscopic geometrical constriction such as surface waviness is often encountered in the electronic components. For instance, the contact interface between the heat sink and the CPU chip, the relay contact, and so on could be given as the representative examples. In these interfaces, the heat flow would be fairly distorted depending strongly on the apparent contacting area and its periphery interface material.

In the present study, for the purpose of visualizing not only the temperature field but also such distortion of the heat flow in the vicinity of the contact interface, the Excel analysis has been introduced as a visually oriented numerical calculation method along with the thermal network of equations expressed by the two-dimensional cylindrical coordinates system. In the Excel analysis, a concrete image or a computational domain corresponding to the physical model can be drawn directly on the spreadsheet, and in addition, by simply making use of Worksheet Analysis, writing and debugging are visually conducted with ease. Iterative calculations are carried out automatically, and the computation is repeated until the prescribed iteration number or convergence criterion is satisfied. Concerning calculated results, numerical values shown in the computational domain are immediately visualized using the Chart Wizard. Therefore, by using the spreadsheet software like Excel, even the students and younger researchers who have just started to study numerical analysis can perform calculations easily and quickly without studying any special knowledge about the computer language, and in addition without writing lengthy computer programs.

Both the temperature field and the heat flow distortion in the vicinity of the contact interface has been visualized and clarified from the numerical calculations corresponding to the representative experimental conditions.

Numerical visualization, Heat flow, Temperature field, Thermal contact resistance, Constriction resistance

Laser Induced Fluorescence (LIF) technique is highly used to determine temperature, pressure or concentration with different modes of operation. Most LIF studies concern combustion process or pollutants formation especially in IC-engines. Other LIF implementations exist for example for shock tube applications. Because LIF signal depends on temperature, pressure and species concentration, different ways enable to determine these quantities from LIF technique. For example, according to experimental conditions, temperature can be obtained from single color detection technique, single excitation two-colors detection technique or dual-excitation wavelength technique. Different tracers are commonly used such as toluene or acetone. Recently investigations have been done on spectroscopy properties of anisole. This work presents fluorescence measurements of this last one tracer, anisole. First, anisole fluorescence was induced by a pulsed Nd:Yag laser to obtain instantaneous temperature from planar LIF measurements. Then, experimental set-up has been modified in order to perform continuous local measurements using an arc lamp source as continuous excitation. All calibration is done in a high pressure and high temperature cell.

In the first experiment, a frequency-quadrupled and pulsed Nd:Yag laser (266 nm, 90 mJ/pulse at 10 Hz) was used to excite anisole molecule. Spectroscopy measurements enabled to determine optimal spectral bands integration in order to make single excitation two-colors detection temperature measurements. Pressure, temperature and gas composition influence on anisole fluorescence has been characterized for pressures from 0.2 MPa to 4 MPa and temperatures from 473 K to 1,000 K. Data obtained can be used for calibration in order to perform quantitative temperature measurement given by the fluorescence signal ratio of the two colors band integration.

The second part of this study aimed to modify the first experiment in order to be able to measure gas temperature with a high acquisition frequency. Pulsed laser excitation has been replaced with a continuous 1 kW HgXe arc lamp source. This source has a continuous emission spectrum that matched anisole absorption cross section. The higher wavelengths are low pass filtered. Summation of irradiance for every wavelength of this spectrum gives a high excitation power value. A spectroscopy investigation show the modification of a large spectrum excitation on fluorescence spectrum shape (spectrum range and fluorescence peak). Determination of the two colors optimal spectral bands detection are proposed again.

These two approaches are investigated and compared and calibration data curves are given in nitrogen for a large range of pressure and temperature.

LIF, spectroscopy, anisole, thermometry

A new approach for predicting surface temperature and heat flux from the embedded time domain thermocouple in the hypersonic wind tunnel is presented herein. The method evaluated surface temperature and heat flux of one dimension half space plate in time domain point of view. Time domain analysis involved using the heat equation (combination of general and particular laws) for obtaining an integral relationship for estimating the heat flux.
This paper presented flat plate experiments at M6 (stagnation temperature 473K and stagnation pressure 2.0Mpa) in the hypersonic wind tunnel which showed the new embedded thermocouples method comparing with the thin wall model method. The testing results of the two methods showed that the in-depth method is better in temperature and heat flux measurement.

Heat flux, time domain, flat plate, wind tunnel test

This experimental study measured the detailed Nusselt numbers (Nu) distributions over two opposite leading and trailing walls of a rotating parallelogram square two–pass channel enhanced by transverse ribs using infrared thermography. The effects of Reynolds (Re), rotation (Ro) and buoyancy (Bu) numbers on local and area-averaged Nusselt numbers (Nu and ) over the rotating leading and trailing ribbed endwalls were examined at the test conditions of Re=5,000~20,000, Ro=0~0.15 and Bu=0.002~0.029 as the first attempt to reveal the combined rotating buoyancy and Coriolis force effects on the detailed heat transfer properties of the rotating parallelogram two-pass channel with transverse ribs.

rotating parallelogram channel, turbine blade cooling

Visualization of flows in wind tunnel testing can provide direct insights into the problem at hand. The complexity, cost and responsiveness of the visualization method is of crucial importance for practical use. In this work we aim to develop a cost-effective and fast visualization method based on tracking soap bubbles in real time with a set of novel cameras. The Dynamic Vision Sensor (DVS) was developed at the Institute of Neuroinformatics, University of Zürich [1]. It is a special type of “smart” camera since it follows an event-driven approach. Each pixel independently registers any change of relative intensity and generates an event, composed of the pixel identification, the time instant of the change and its sign. The result is a continuous stream of events that is sent to a computer for further analysis. The high temporal resolution of 1μs allows to capture very fast processes which can otherwise only be achieved by high speed cameras. The advantage of the DVS is the inherent reduction of data, since only the changes in the scenery are recorded, allowing fast data transmission and post-processing on standard hardware. The DVS has already been used for particle tracking in micro-fluidic flows [2]. In the wind tunnel helium filled soap bubbles are used as neutrally buoyant tracers with low inertia and good visibility. For a 3D reconstruction of the particle tracks, at least two cameras at different viewpoints are required. In the present system a third camera is used to increase the probability of detection and to minimize the appearance of ghost particles. A Kalman filter is used to track the bubbles in each camera individually, from which the 3D particle tracks are reconstructed as a function of time. As a result the local velocity is readily derived. Preliminary results from measurements in a medium sized wind tunnel are presented (e.g. separation around an Ahmed body) and the new tracking system’s performance will be discussed.
[1] Lichtsteiner, P., Posch, C., Delbruck, T. & Member, S. Temporal Contrast Vision Sensor. Work 43 (2), 566–576, 2008.
[2] Drazen, D. & Lichtsteiner, P. 2011 Toward real-time particle tracking using an event-based dynamic vision sensor. Experiments in Fluids pp. 1465–1469.

PTV, large-scale, wind tunnel, dynamic vision sensor

Time-resolved high-speed imaging of shock wave cavity interactions

by

D.A. MacLucas (1), B.W. Skews (1) and H. Kleine (2)

(1) Flow Research Unit, School of Mechanical, Industrial and Aeronautical Engineering, University of the Witwatersrand, Johannesburg, 2050, South Africa
(2) University of the New South Wales, School of Engineering and IT, Canberra, ACT 2600, Australia

Email: dmaclucas@gmail.com (1)

Analysis of shock wave interactions remains predominantly experimentally-based. Flow visualisation techniques are employed to capture the interaction thereby providing the means to examine complex shock wave behaviour [1]. Time-resolved high-speed imaging in combination with density-based flow visualization techniques have provided a unique opportunity to revisit shock wave cavity interactions. The ability to track various flow features frame-by-frame in high resolution allows one to examine the highly transient flow features developed in the cavity field. Qualitative and quantitative flow visualization systems provide valuable information on the nature of the highly-transient flow field developed behind the various reflections patterns. These techniques have provided unique insight into the development of shock wave focusing.

The preeminent study in the field of shock wave focusing by Sturtevant and Kulkarny [2] relied on shadowgraphy to capture the interaction of plane shock waves in air with parabolic profiles. Shadowgraphy was valuable for ascertaining shock waves and shear layers in the flow field but being only qualitative in nature the authors missed the development of various expansive and compressive fields which form part of the shock wave focusing process. This works employs both qualitative and quantitative techniques to examine the complex flow field developed during the interaction of a plane shock wave with a concave profile. Both direction-indicating schlieren and shearing interferometry are used to visualize the flow field. Results indicate that the flow field is more complex than that described by Sturtevant and Kulkarny [2]. In addition, this work will demonstrate the significant benefits of employing polychromatic shearing interferometry in the analysis of two-dimensional shock wave interaction cases.


References

[1] Skews B.W., and Kleine H. (2007) Flow features from shock wave impact on a cylindrical cavity. J. Fluid Mech. 580, pp 481-493.
[2] Sturtevant B., and Kulkarny V.A. (1976) The focusing of weak shock waves. J. Fluid Mech., 73, pp 651-671.

shock wave focusing, shearing interferometry, direction-indicating colour schlieren, concave profiles

The lifetime-based PSP measurement has several advantages compared to the intensity-based method however it is still not a common PSP technique in wind tunnel testing. One problem is a non-uniformity of lifetime distribution on the coating. Theoretically PSP lifetime is independent to an excitation pattern, dye concentration and paint thickness, however, the lifetime distribution is sometimes not uniform on the coated PSP. First of this work, PtTFPP-based PSP for lifetime-based method is developed to improve the lifetime uniformity. We especially focused the effect of basecoat material and polymer. In the second part, the lifetime-based PSP method is applied to a transonic wind tunnel test. As a result, pressure distributions can be obtained by the lifetime-based method at M = 0.5 and 0.3. PSP results show characteristic pressure pattern on a delta wing model.

Pressure-Sensitive Paint, Lifetime-based Method

Numerous theoretical and experimental studies were recently activated due to disagreement appeared under practical conditions between experimental observations and zero-dimensional, homogeneous gas phase predictions based upon any of the available chemical kinetics models. It was found that auto-ignition delay times at temperatures below 1100 K are strongly influenced by various experimental perturbations, therefore the main problem is considered now to be connected with the correct experimental data interpretation. Experiments show that ignition times are very sensitive to the fluid dynamic effects, presence of contaminants, and catalysis from particles or surface materials. Even though these non-ideality of experimental conditions have been known for the long time, their importance has been not taken into account in the theoretical modelling due to lack of experimental information. In the present study, high-speed digital imaging has been used to investigate the reasons of too early auto-ignition of gases under conditions of rapid compression. Experiments were carried out in rapid compression machine for the most important and therefore most studied hydrogen-air and methane-air mixtures at temperatures below 1100 K and pressures 0.8-2 MPa. Additional runs were performed for fuel free and oxygen free mixtures at the same temperatures and pressures. High-speed visualization showed that auto-ignition at studied conditions is non-uniform and always starts from one or several points. The narrow tracks, probably produced by burning particles, were registered on long exposed images. The same pictures were observed in experiments with fuel free mixtures containing oxygen. It allowed us to suggest that recorded tracks on the long exposed and bright spots on the short exposed images are connected with small particles, which can’t be completely excluded from test volume. At definite conditions (temperature, pressure and particles size), these particles can be auto-ignited earlier than gaseous reactive mixture and cause it non-uniform ignition. We proved the possibility of this phenomenon during this study and argued that the main reason of observed discrepancy and big scattering of experimental data caused by the presence of impurities in the form of ultra-fine particles in reactive mixture.

rapid compression machine, hydrogen, methane, auto-ignition, high-speed digital imaging

A two-phase flow often exhibits a complicated three-dimensional structure by nature even in a simple vertical pipe. In order to model such a complicated flow structure and to validate multiphase flow CFD, experimental database for three dimensional velocity and void fraction distributions are crucial. The paper addresses an algorithm to measure three-dimensional velocity of individual bubble with a bubble paring scheme. The bubble paring scheme finds a pair of bubble in two sets of wire-mesh sensor data to determine the direction and magnitude of velocity vector for each bubble. The devised scheme was applied to the vertical upward air-water flow (jG=0.64m/s, jL=0.64m/s) in a large diameter pipe (i.d. 224mm). The bubble pairing scheme visualized the developing process of two-phase flow: large bubbles coalesced with each other to move toward the center, while the rest of bubbles broke up into smaller bubbles and decelerated.

bubbly flow, bubble identification, bubble tracking velocimetry, void fraction, bubble size, wire-mesh sensor

Heat transfer in a three-phase interface has been drawn much attention to improve the efficiency and reliability of heat exchangers. There are some studies on the temperature and heat transfer distributions in a three-phase interface. However, there is an issue in these studies due to the use of an infrared (IR) camera. In the temperature measurement by an IR camera, a non-transmissive film black film is needed for a precise measurement. However, gas-liquid behavior on a heated surface cannot be observed through the heated surface by an IR camera. Thus, it is difficult to investigate the relation between a three-phase interface and a heat transfer on a heated surface. In this study, we propose a simultaneous measurement technique of temperature distribution and gas-liquid interface behavior at a heated surface during boiling using the temperature-sensitive paint (TSP) technique. The TSP technique allows us to measure both temperature distribution and gas-liquid interface behavior through the transmissive TSP film. In this study, we employed a stereo-viewer to simultaneously obtain the TSP emission and gas-liquid interface images. A preliminary experiment of flow boiling in a micro-gap channel is conducted. The size of the channel was 10 mm in width, 0.5 mm in height, and 30 mm in the heated length. The test fluid was FC-72 with mass velocity of 300 kg/m2s. Hot water (338 K) was used as a heating source. The temperature distribution of the FC-72 heated surface and the gas-liquid interface were successfully measured. We investigated the relation between the gas-liquid interface and the temperature distribution (heat flux) by a direct comparison with precise alignment.

TSP, Boiling

The authors consider the flow between co-rotating disks, namely, the disks which rotate co-axially in the same direction at the same angular velocity, with a narrow gap enclosed by a stationary shroud at their circumferences. The flow often accompanies azimuthally-fluctuating instabilities; non-axisymmetric secondary flows nears the shroud. In this study, the authors experimentally and numerically research the flow in torus-vortex modes, in addition to core-shape modes.In experiments, the authors visualise the meridian plane (r-z plane) between co-rotating disks, using a high-speed video camera and a YAG laser to carry out particle-image-velocimetry (PIV) analyses. Based on such PIV results, the torus-vortex modes are defined. And by numerical calculations, we reveal the details of flow structure in those modes.

Rotating Flow, Numerical Calculation, Flow Visualisation, Rotating Disk, PIV Analysis

Particle image velocimetry (PIV) is one of the time-of-flight techniques based on particles seeded in a flow. It is difficult to apply this technique to transonic and supersonic flows because of the unreliable particle traceability. Although the PIV technique has such a difficulty, it has a specific benefit; i.e., flow velocities on a laser sheet plane can be measured non-intrusively with a high spatial resolution.
Molecular tagging velocimetry is also a time-of-flight technique. In this technique, molecules are seeded in a flow as tracers. This technique does not have the abovementioned benefit because a laser is injected into a flow as a beam. Instead, we do not have to worry about the particle traceability.
The final goal of our study is to apply the PIV technique to high-speed flows in which gas accelerates and decelerates rapidly. In order to achieve this, the particle traceability in transonic and supersonic flows is investigated by measuring the same flow with both techniques of PIV and MTV.
Two types of flow are selected as tested flows. One is a transonic flow at a Mach number of ~1.5 impinging on a circular cylinder. In this flow, a bow shock wave appears in front of the cylinder; across the shock wave the flow decelerates abruptly to a subsonic speed. The other flow is an underexpanded jet discharged from an orifice. This jet has an isentropic expansion region in which the flow accelerates rapidly to a Mach number of ~3.5 and a Mach disk across which the flow decelerates abruptly to a subsonic speed.
In the PIV measurements, dioctyl sebacate (DOS) particles are seeded into the flows as tracers. The diameter and density of the particles are ~1μm and 913.5kg/m3, respectively. For the transonic flow, the experimental results reveal that the PIV data starts to deviate from the MTV data just behind the bow shock wave. The maximum difference between the two velocity data is found to be ~75m/s. However, the PIV data becomes identical to the MTV data again ~0.8mm downstream of the bow shock wave. The results for the underexpanded jet reveal that the particles cannot trace the flow not only behind the Mach disk but also in the isentropic expansion region. The maximum differences between the two data are found to be ~110m/s and ~270m/s in the expansion region and behind the Mach disk, respectively.

Particle image velocimetry, Molecular tagging velocimetry, transonic flow, supersonic flow, shock wave

Sustainable power generation resulting in low pollutant emissions, such as CO2 and NOx, poses a very challenging task in the near future. To cope with ever more stringent regulations, premixed combustion of hydrogen-rich fuels in gas turbines is a worthwhile approach. This method, however, involves the risk of flame flashback from the desired flame position into the premixing section, leading to catastrophic failure of the machine components that are not designed for such high temperatures. The objective of the current study is to characterize the transition from stable flame configuration to flashback in a generic H2-air combustion system with very high temporal and spatial resolution. For this purpose, Particle Image Velocimetry (PIV) and Planar Laser-Induced Fluorescence (PLIF) are used to gain insight into the initial upstream propagation of the flame, which occurs along the wall boundary layer. To characterize the interaction of the flame with the flow in detail, both measurement techniques are applied to very small fields-of-view using (UV) long-distance microscopes. The repetition rates are 20 kHz for PLIF and 3 kHz for PIV, respectively. The PIV and PLIF signals are captured by means of high-speed cameras (Photron FASTCAM SA-X). For PLIF, the high-speed camera is combined with an image intensifier (Hamamatsu C10880-03) and appropriate filters. During both the PLIF and the PIV measurements, a second image-intensified high-speed camera (Photron FASTCAM-ultima APX-I2) simultaneously captures the OH*-chemiluminescence from a perspective perpendicular to that of the PLIF/PIV camera for further flame characterization.

The results of these µ-PIV measurements show that there is negligible influence of the flame on the approaching flow in the stable case. During the onset of flashback, however, the velocity profile of the approaching flow is distinctly distorted by the presence of the flame inside the premixing duct. The flow directly upstream of the flame is retarded and deflected around the leading flame tip. The shape of the flame during flashback is evaluated based on the PIV seeding particle density, which is greatly reduced across the flame front. It could be shown that the flame shape determined by means of the PIV seeding density images agrees very well with that determined in the µ-PLIF measurements, which shows that seeding particle images can be used for proper detection of flame fronts. The outcome of this research helps understanding the mechanisms involved during flame flashback and is therefore highly relevant for the safety of combustion systems employing fuel premixing.

PLIF, PIV, High-Speed, Premixed Combustion, Flame Flashback, Flame-Flow Interaction, Long-Distance Microscope

The talk will start with the description of the recent progress made by the speaker in developing a novel molecule-based flow diagnostic technique, named as Molecular Tagging Velocimetry and Thermometry (MTV&T), for simultaneous measurements of flow velocity and temperature distributions in fluid flows. Unlike most commonly-used particle-based flow diagnostic techniques such as Particle Image Velocimetry (PIV), MTV&T utilizes specially-designed phosphorescent molecules, which can be turned into long-lasting glowing marks upon excitation by photons of appropriate wavelength, as tracers for both flow velocity and temperature measurements. The unique glamour of the MTV&T technique will be demonstrated from the application examples to study the thermal effects on the wake instabilities behind a heated cylinder, visualization of the unsteady heat transfer and phase changing process within micro-sized icing water droplets, and transient surface water transport processes pertinent to aircraft or wind turbine icing and de-/anti- icing applications.

The second part of the talk will introduce the speaker’s recent research on wind turbine aeromechanics and wake interferences. The experimental studies are conducted in a large-scale Aerodynamic/Atmospheric Boundary Layer (AABL) Wind Tunnel. An array of scaled Horizontal Axial Wind Turbine (HAWT) models are placed in atmospheric boundary layer winds with different mean and turbulence characteristics to simulate the situations in onshore and offshore wind farms. The effects of the relative rotation directions of downstream turbines with respect to the upstream turbines, array spacing and layout, and the terrain topology of wind farms on the turbine performances and the wake interferences are investigated in detail. In addition to measuring dynamic wind loads (both forces and moments) and the power outputs of the HAWT models, a high-resolution Particle Image Velocity (PIV) system is used to conduct detailed flow field measurements to quantify the characteristics of the turbulent wake vortex flows and the wake interferences among the HAWTs. The detailed flow field measurements are correlated with the dynamic wind loads and power output measurements to elucidate underlying physics in order to gain further insight into the characteristics of the dynamic wind loads and wake interferences among multiple wind turbines for higher total power yield and better durability of the wind turbines in atmospheric boundary layer (ABL) winds.

Molecular Tagging Velocimetry and Thermometry (MTV&T) technique, mutiphase flow and phased changing flows, aircraft icing, wind turbine aeromechanics and wake interferences

Abstract
Unsteady transonic flows in diffuser have become increasingly important, because of its application in new propulsion systems. In the development of supersonic inlet, air breathing propulsion systems of aircraft and missiles, detail investigations of these types of flow behavior are very much essential. In these propulsion systems, naturally present self-sustaining oscillations, believed to be equivalent to dynamically distorted flow fields in operational inlets, were found under all operating conditions. The investigations are also relevant to pressure oscillations known to occur in ramjet inlets in response to combustor instabilities. The unsteady aspects of these flows are important because the appearance of undesirable fluctuations generally impose limitation on the inlet performance. Test results of ramjet propulsion systems have shown undesirable high amplitude pressure fluctuations caused by the combustion instability. The pressure fluctuations originated from the combustor extend forward into the inlet and interact with the diffuser flow-field. However, it is found that for some configurations such diffusers may exhibit self-sustained oscillations, which impose major limitations on vehicle performance. Depending on different parameters such as the diffuser geometry, the inlet/exit pressure ratio, the flow Mach number, different complicated phenomena may occur. The most important characteristics are the occurrence of shock induced separation, the length of separation region downstream of the shock location, and the oscillation of shock location as well as the oscillation of the whole downstream flow. In order to study the above mentioned phenomena, a high order LES turbulence model developed by the author (putting emphasis on unsteady turbulence characteristics) is assessed with some experimental data on the self-excited shock oscillation phenomena. The whole diffuser model configuration including the suction slot located at certain axial location around the bottom and side walls to remove boundary layer, are included in the present computation model. The time-mean and unsteady flow characteristics in this transonic diffuser as a function of flow Mach number and diffuser length are investigated in detail. The results of study showed that in the case of shock-induced separation flow, the length and thickness of the reverse flow region of the separation-bubble change, as the shock passed through its cycle. The instabilities in the separated layer, the shock /boundary layer interaction, the dynamics of entrainment in the separation bubble, and the interaction of the travelling pressure wave with the pressure fluctuation region caused by the step-like structure of the suction slot play very important role in the shock-oscillation frequency.

Turbulence, shock/boundary layer interaction, characteristic frequency, length scale, large scale motion

This paper describes a method to measure the emission and absorption of an enclosed axis-symmetric flame. The radial spectral absorption coefficient as well as the emission is obtained from line-of-sight integrated measurements using an enhanced technique.

The procedure is based on typical Abel-type transforms found in literature. These routines require a flame burning in the open. However, the flame has to be enclosed in many situations, e.g. by a tube. This significantly alters the optical path. Such an experimental setup cannot be handled by the common routines.

The proposed technique shows the following concept: The camera is treated as either a point-shape or a parallel ray detector. Using ray tracing, the path of the radiation is reconstructed for each pixel on the sensor. The rays of the bundle pass the flame as oblique rays. The axis-symmetric flame is treated to consist of discretized homogeneous shells. The number of shells is equal to the number of rays passing through the flame. Along the convolution of shells and the oblique rays, the radiation transport equation is set up. This yields a set of equations that can be solved to get the radial absorption and emission coefficients from the sensor data.

The method is demonstrated on a laminar hydrogen-oxygen jet flame at elevated pressure. The UV absorption and emission of the OH radical is measured and compared with data from numerical simulations.

Flame Absorption, Flame Emission, Jet Flames, Abel transform

The purpose of this investigation is to research and develop a new type water turbine, which is appropriate for low-head open channel, in order to effectively utilize the unexploited hydropower energy of small river or agricultural waterway. The application of placing cross-flow runner into open channel as an undershot water turbine has been under consideration. As a result, a significant simplification was realized by removing the casings. However, flow field in the undershot cross-flow water turbine are complex movements with free surface. This means that the water depth around the runner changes with the variation in the rotation speed, and the flow field itself is complex and changing with time. Thus it is necessary to make clear the flow field around the water turbine with free surface, in order to improve the performance of this type turbine. In this research, the performance of the developed water turbine was determined and the flow field was visualized using particle image velocimetry (PIV) technique. The experimental results show that, the water depth between the outer and inner circumferences of the runner decreases as the rotation speed increases. In addition, the fixed-point velocities with different angles at the inlet and outlet regions of the first and second stages were extracted.

Water Turbine, Undershot Cross-Flow Turbine, Open Channel, Free Surface

Thermo-physical properties of magnetic fluid were measured experimentally at various temperatures, in order to evaluate those temperature dependencies. Heat transfer by natural convection was also investigated in a horizontal enclosed rectangular container filled with the tested magnetic fluid, which was heated at the lower surface and cooled at the upper surface. It was found that the heat transfer coefficient of the magnetic fluid keeps good agreement with the conventional heat-transfer correlation of natural convection heat transfer in a horizontal enclosed rectangular container by applying the values of thermo-physical properties obtained in the present work. Therefore, the measured thermo-physical properties are reliable and can be used as a thermo-physical database of the magnetic fluid.

Natural Convection, Heat Transfer, Thermo-Physical Property, Magnetic Fluid, Horizontal Enclosed Rectangular Container

Research using a curved wall jet burner has revealed important aspects of turbulent premixed flame dynamics and structure. The proposed geometry of this burner enables in forming a recirculation zone upstream for flame stabilization. Further downstream there is an intense turbulent interaction-jet region followed by the merged-jet region. Increasing the velocity of the reactants controls the characteristic time and length scales of the turbulence at the interaction-jet region and creates a highly strain rate capable of quenching the post-flame at the merged-jet region as the upstream flame zone accommodated only in the recirculation zone. Proposing a central port to supply R=10%, 20% and 50% of the total fuel in the pre-mixture tangentially to the recirculating flow upstream improves the flame stability as R intensifies the recirculation zone and reduces the likelihood of post-flame quenching. A series of simultaneous time-resolved measurements of particle image velocimetry (PIV) and planar laser-induced fluorescence (PLIF) of the OH radical for three turbulent propane/air flames were conducted to interpret such characteristics. High speed OH-PLIF images show the flame intermittency due to the strain rate influence. Flames of R=0% propagate in a highly irregular fashion, decreasing their influence on the flow field and are characterized by an extreme intermittency and experience different local flow fields. Such flame intermittency at the same velocity of reactants is unlikely as R increases. This is attributed to the reduction of the heat losses associated with effective air entrainment at the position of high strain rate by supplying a percentage of fuel (R) through the central port.

Turbulent premixed flames, PIV, OH-PLIF, Flame stabilization, CWJ burner

In this paper the improved Background Oriented Schlieren technique called CBOS (Colored Background Oriented Schlieren) is described and used to reconstruct density fields of three-dimensional flows. The Background Oriented Schlieren technique allows to measure the light deflection caused by density gradients in a compressible flow. For this purpose the distortion of the image of a background pattern observed through the flow is used. In order to increase the performance of the conventional Background Oriented Schlieren technique, the monochromatic background is replaced by a colored dot pattern. The different colors are treated separately using suitable correlation algorithms. Therefore, the precision and the spatial resolution can be highly increased.
The experiments are carried out in the 0.2 m  0.2 m supersonic blow-down wind tunnel of ISL with a freestream Mach numbers of 3. The spike-tipped model used for this investigation has a cylindrical centerbody (D = 40 mm) and is mounted on a sting assembly along the wind-tunnel centerline. The Reynolds number ReD based on the model diameter is 2.1  106. These flow conditions lead to very strong shocks in the front region of the model. Therefore a special arrangement of the different colored dot patterns in the background allows astigmatism in the region with high density gradients to be overcome.
An algebraic reconstruction technique (ART), taking into account forward and backward projections, is then used to reconstruct the density field of unsteady flows around a spike-tipped model from CBOS measurements.
It could be shown that the accuracy and the spatial resolution of the CBOS technique allows us to obtain a reliable reconstruction of the nearly axial symmetrical density field of unsteady flows. Especially for complex flows around a spike-tipped model the distribution of the density helps considerably to understand the flow phenomena.

supersonic flow, unsteady spike flow, schlieren technique, algebraic reconstruction

VISUALIZATION OF AN EXPANSION FAN/SHOCK WAVE INTERACTION

L. J. Nel 1), B. W. Skews 2) and K. Naidoo 1)

1) Council for Scientific and Industrial Research, Defence Peace Safety and Security, Aeronautics Systems Competency, Pretoria, 0001, South Africa
2) Flow Research Unit, School of Mechanical, Industrial and Aeronautical Engineering, University of the Witwatersrand, Johannesburg, 2050, South Africa

Email address for correspondence: lnel@csir.co.za


In supersonic flow, shock waves and expansion waves occur as a mechanism for the fluid to adhere to imposed boundary conditions. Examples of this include the alteration of flow direction around an object as well as specific driving or back pressures. The flow field resulting from an expansion fan/shock wave interaction is of fundamental interest. In addition, there are a number of practical applications where knowledge of such a phenomenon and the resultant flow behaviour would be beneficial. Instances where this is true are store carriage and release from aircraft, supersonic engine intake design and formation flying. Flow visualization provides the mechanism for studying such an interaction.

This paper focuses on visualizing the interaction between an expansion fan generated by a single wedge and a shock wave generated by another at various Mach numbers, both numerically and experimentally. Previously, this phenomenon has only been studied analytically [1] and numerically [2] with a focus on intake design. In this study, the concentration is on experimental investigation of external flows, relating to store release. A classical schlieren setup is used for the experimental visualization. Since the expansion fan is comprised of a series of Mach waves, sensitivity of the system is an important factor. Various cut-off techniques were investigated to determine the most effective method for conveying qualitative data about the shock wave/expansion fan interaction and the resulting flow field. The interesting phenomena occurring as a result of this interaction will be discussed and contrasted with data from numerical simulations.

REFERENCES
[1] Li, H. & Ben-Dor, G. Oblique-Shock/Expansion-Fan Interaction - Analytical Solution. AIAA, Vol. 34, no. 2, pp. 418-421, 1996.
[2] Yao, Y., Li, S. G. & Wu, Z. N. Shock reflection in the presence of an upstream expansion wave and a downstream shock wave. J. Fluid Mech., Vol. 735, pp. 61-90, 2013.

Expansion fan, shock wave, interaction, visualization, schlieren

In recent years, the human activity range is expanding to varied gravity environments such as Mars exploration and the construction of International Space Station. To promote development in space or low gravity environments, a fire safety assessment must be assessed under the different gravity level to normal.　Fires should be extinguished in their initial stages to protect human life.　To improve our understanding of the effects of gravity on flame characteristics, we conducted an experimental investigation on small-scale liquid pool fires and downward spreading flame over thin combustible solid under different gravity levels to normal.　The drop tower facility at Hirosaki University in Japan was used to obtain arbitrary low gravity acceleration. Our measurements focus on the flow visualization around the flame by a particle-track laser-sheet technique (PTLS) combined with a high-speed camera under low gravity environments. Flow visualization was performed under a normal gravity environment (G=1) and low gravity environment (G=0.55) to investigate the effect of gravity on induced air flow assisted by buoyancy. We established a thin laser sheet (1-mm thick) using a 50mW Nd:YAG/YVO4 solid laser. Flow visualization at the vertical plane along a center axis was conducted, and the flow profiles were analyzed. The commercially available talc particles generated by a particle feeder were supplied from a slit near the rim in the case of a liquid pool fires, and it were supplied from the bottom of flame in the case of a thin combustible solid. Although the particle injection velocity was less than 0.04 m/s, a sufficient seeding rate and density were achieved. Two high speed video cameras recorded these particles and the pool flame from two lateral perspectives. Both cameras were placed perpendicular to the laser sheet, and their exposure times were set at 1/320 s. One camera (30 frames/s) recorded the visible flame, and the other lateral-view camera (300 frames/s) recorded the particle trajectories using a band pass filter of 532nm±5%. The images of the two cameras were superimposed when analyzed. The results shows that the flow velocity declines with decreasing gravity level, especially, the normal flow velocity component to the flame sheet, Vn, decreases. We summarized the Peclet number including Vn was related with the Grashof number. When the Grashof number closes to 0, the Peclet number asymptotically approaches to unity.

PTLS, low gravity, small-scale liquid pool fires, thin combustible solid

The momentum added or induced by a plasma actuator controlling separated flow over an airfoil is visualized by numerical simulation. Two significant mechanisms of flow control are clearly visualized by the imaginary ink which is computed by the passive scalar: direct momentum addition and freestream momentum induction. The latter is utilized in the case of burst mode (duty cycle) actuation and the much momentum is induced when the vortex paring occurs.

Plasma actuator, Numerical simulation, Passive scalar

Recently, many research on various properties of micro bubble are performed. Micro bubbles are defined as bubbles of 50μm or less in diameter. Micro bubbles are known to have friction reduction effect, cleansing effect, sterilization effect, physiological active effect and many more. In this study, the skin friction of vertical circular tube that is widely used in industry is investigated. Also the vertical pipe flow of gas-liquid two-phase fluid containing the micro bubbles were analyzed by flow visualization.The purpose of our study is to clarify the drag reduction mechanism of a vertical circular pipe flow by micro bubbles. A circulating water system basically designed to measure pipe friction loss is used.  The water was pumped from the water storage tank to the vertical test section. Flow rates can be adjusted by controlling the valve placed between the tank and the test section. micro bubbles were generated continuously in the tank throughout the experiment and its distribution was observed by using digital still camera and digital microscope. The flow rate was measured by the gravimetric method and the bulk velocity was calculated from the flow rate. The pressure loss was measured by manometers. Visualization of pipe flow is carried out by a laser light sheet and a high speed camera. As the results pipe friction loss reduction effect was confirmed by injecting micro bubbles. it was found that the velocity gradient, the turbulent intensity and the wall shear stress become small by including micro bubbles.

Microbubble, Skin friction reduction, Pipe friction, Void fraction, Flow visualization

Clarification of flame behaviours and flame-wall interaction in a constant volume vessel is of great importance for promotion of efficiency of combustors, especially SI engines. Direct numerical simulation (DNS) of turbulent hydrogen-air premixed flames in a constant volume rectangular vessel at relatively high Reynolds number is conducted by considering detailed kinetic mechanism and temperature dependence of the transport and thermal properties. The detail kinetic mechanism including 12 reactive species and 27 elementary reactions is used to represent the hydrogen-air flames. The sizes of the vessels are 20.0 mm x 5.0 mm x 20.0 mm and 40.0 mm x 5.0 mm x 40.0 mm. The preheating temperature, the wall temperature and the equivalence ratio are set to 700 K, 450 K and 1.0 respectively. In this study, flame behaviours, heat transfer and heat flux characteristics in a constant volume vessel have been investigated by scientific visualizations of several important quantities obtained by DNS. After the flame is ignited, the flame propagates from the ignition kernel. The flame displacement speed normal to the wall decreases gradually as the flame approaches the wall. After the flame impinges on the wall, the flame propagates along the wall. Finally, the flame surface is found only near the eight corners. The flame is also strongly affected by the growth of the internal pressure which is caused by the temperature rise in the vessel. Since the pressure increase makes the flame thickness thin, the heat release rate of each flame element is augmented. The pressure rise due to the dilatation also enhances turbulence and finer scale vortices appear, which make the flame surface more complicated and result in an increase of the flame surface area. Due to the increase of the mean pressure in the vessel, the maximum wall heat flux induced by the flame front is enhanced during the combustion. The maximum wall heat flux on each wall for both vessels are approximately proportional to the mean pressure as the flame impingement occurs. It suggests a possibility that the wall heat flux can be described as a function of the mean pressure.

direct numerical simulation, constant volume vessel, heat transfer characteristics

It is known that small amount of surfactant additive reduces turbulent friction drag. The drag reduction effect appears in a certain Reynolds number range. In the drag-reducing regime, friction drag decreases with the Reynolds number, and it recovers in the drag-recovering regime which comes after the maximum drag-reduction. This study aims to clarify the relationship between drag-reduction state and change of turbulent flow structure by detailed visualizations of velocity field and statistical characteristic during the both drag-reducing and drag-recovering regimes. The dual plane stereoscopic PIV (DPSPIV) is operated by double pulsed Nd:YAG laser (532 nm, 50 mJ/pulse) and 4 CCD cameras (2048 x 2048 pixels). Each two laser sheet is adjusted to have 200 um FWHM and two PIV planes are 350 um apart and in parallel. PIV interrogation window size is 24 x 48 pixels for wall-normal and spanwise directions. The energy dissipation rate and second invariant of velocity gradient tensor Q are directly evaluated by the velocity gradients obtained by DPSPIV. Measurement has been done for water flow with and without surfactant additive in circuit of 52 mm diameter pipe for 12 Reynolds numbers. Measurement area is 18.4 mm x 18.4 mm and perpendicular to the mean flow. In the drag-reducing regime, velocity fluctuations are suppressed, and they recover progressively in drag-recovering regime. In the intermediate state of drag-recovery, the streamwise velocity fluctuation recovers prior to the wall-normal component. The Reynolds shear stress is very small in the drag-reducing regime, and reaugments together with wall-normal velocity fluctuation. In the outer region, the profiles of mean streamwise velocity normalized by the friction velocity increases in the drag-reducing regime, then it approaches to no drag-reduction state in drag-recovering regime. In addition, spectrum and Proper Orthogonal Decomposition (POD) mode analyses are conducted. The vorticity spectra for circumferential direction has low energy in high frequency components in drag-reducing regime. It reincreases from the wall in drag-recovering regime. Several representative POD modes of vorticity show the layered structures expanding apparently larger than the present measurement area in circumferential direction, and such structures are observed until the friction drag recovers. Furthermore, the coherent fine scale eddies are extracted from the present PIV data based on the instantaneous distributions of Q. The number of identified eddies decreases drastically in the drag-reducing regime compared to the water flow case. This can be a possible explanation for the decrease of velocity fluctuation and the Reynolds shear stress.

dual-plane stereoscopic PIV, turbulent pipe flow, drag-reduction with surfactant additives

The contact line of liquid film falling down a slope tends to be unstable to viscous fingering. Previous studies[1][2], both experimentally and numerically, pointed out the finger geometry strongly depends on the contact angle; the effect of the dynamic contact angle, however, has rarely measured or discussed. In this study, Color Coding Method, which has been firstly developed by Zhang et al.[3], is applied to measure the surface geometry involving the moving contact line of a falling liquid film along an inclined solid surface in order to investigate the effect of the dynamic contact angle on the fingering instability.
Color Coding Method is a two-dimensional, simultaneous measurement system of the surface geometry of liquid. The color light ray, irradiated from below of the flow channel, is refracted at a lens located below the flow channel and at the liquid surface, and then is captured by a color camera. The RGB color luminance information for each pixel is translated into the gradient vector of the surface by using a calibration data table made in advance. The surface geometry is estimated by integrating the obtained values of the gradient vector.
The experiment was performed with a transparent acrylic channel of 1030 mm (flow direction) by 600 mm (span direction). The inclined angle of the channel was 2 ~ 11 degrees. The working fluid was water and ethylene glycol. The static contact angles were 53 degrees for water and 46 degrees for ethylene glycol. The spatial resolution of the obtained image was 0.033 mm/pix and mean resolution of surface gradient is 0.8 degrees.
The obtained dynamic contact angle on the contact line for developing finger took a maximum value around the tip of the finger at which the contact line advanced with maximum speed, and lower value for trough region, at which the contact line was almost at rest. This is consistent with the well-known fact that the dynamic contact angle of the advancing contact line increases with the increment in the moving velocity of the contact line. Such difference in the dynamic contact angle would suppress the destabilization of the contact line since the initial generation of the finger is interrupted by the pressure increase induced by the larger curvature at the tip brought by the higher contact angle compared to that at the trough region.

[1] Silvi N. and Dussan V, E. B., Phys. Fluids 28, 5-7 (1985).
[2] Moyle, D. T., Chen, M. S., Homsy, G. M,. Int. J. Multiphase Flow, Vol. 25, 1243-1262 (1999).
[3] Zhang, X., Cox, C. S., Experiments in Fluids, Vol.17, 225-237 (1994).

Color Coding Method, Contact angle, Contact line, Fingering instability

A typical soccer ball is usually constructed from 32 pentagonal and hexagonal panels. In recent years, however, the Teamgeist and Jabulani balls, constructed from 14 and 8 panels, respectively, have entered the field. Consequently, soccer ball panels have evolved significantly beyond the conventional in terms of their shape and design. Moreover, the recently introduced Cafusa ball has a new 32-panel design and it is used in many soccer leagues. The Cafusa ball is constructed from the same number of panels, viz. 32, as conventional balls. However, the shape of these panels differs substantially from those of the conventional balls. In particular, the ball’s panel orientations can be broadly classified into three types. However, few aeromechanical studies, on the flight and aerodynamic characteristics of these soccer ball panel shapes, have been reported.
Therefore, the present study investigates the flight and aerodynamic characteristics for all orientations of the Cafusa ball, which is constructed from panels of different shapes.
Firstly, a wind tunnel test showed substantial differences in the aerodynamic force acting on the ball, depending on its orientation. Next, substantial differences were also observed in the aerodynamic forces acting on the ball in different directions, corresponding to its orientation and rotation. Furthermore, a test for the ball’s point of impact, using a kicking robot, revealed very large variations in the flight trajectory depending on ball orientation; and hence, ball orientation can be assumed to substantially affect the ball’s flight. Moreover, The 2D-PIV measurements showed that the boundary separation varies depending on its orientation.
Based on these results, we can conclude that the flight trajectory of a soccer ball, which has drawn attention for its panel characteristics, is significantly affected by variations in the panels’ shape, depending on the ball’s orientation and rotation.

ball, football, panel orientation, soccer

Computational Fluid Dynamics (CFD) is a powerful tool for simulating fluid phenomena. It is necessary to visualize CFD simulation results in order to convert physics quantities to intuitive and more understandable images. Ray tracing is considered as one of the best ways for showing the actual shapes of the fluids. However, ray tracing is computationally expensive. In additional, generating photorealistic ray tracing images as post process using visualization software needs to spend a huge amount of I/O time and storage for recording the simulation results in every step. These might cost more than those of the simulation process.
NVIDIA iray is a GPU-accelerated ray tracing engine. It has been integrated into some 3D modeling/rendering software such as 3ds Max and Maya. By driving all the CPU cores and GPUs of the system, NVIDIA iray provides stunning photorealistic images in extremely fast speed.
In this paper, a GPU-based fluid simulator with real-time visualizations using NVIDIA iray is presented. A GPU-accelerated space-time conservation element and solution element (CE/SE) method is implemented using CUDA and applied to solve the shallow water equations (SWEs). And a ray tracing visualization module using NVIDIA iray is implemented and integrated with the SWEs simulation framework to generate photorealistic images on-the-fly during the simulation process. Thus, the images are generated directly without storing the simulation results in every step. Depending on the hardware specification and the complexity of the scene, real-time visualizations or high quality photorealistic images of varying water surface can be generated.
In our experiment results, we can obtain up to 10 FPS real-time rendering for 512 x 384 ray tracing images with a simple environment setting of the scene. On the order hand, a full HD 1920 x 1080 photorealistic image of the water surface of the simulation result, including the transparency and reflection of the environment, can be generated around 90 seconds with 600 iterations by the ray tracing of NVIDIA iray. All the above measurements include both the simulation and visualization process running on a workstation with eight GTX TITAN GPUs.

Ray Tracing, Shallow Water Equations, GPU

This study aims to reduce a shock oscillation in a duct flow with passive control using porous cavity and rods. A shock interaction with a turbulent boundary layer occurs in many aerodynamic devices, which detrimental effects on drag and pressure recovery. Moreover, this interactions between them cause shock oscillation. In addition, the interaction also causes unsteady pressure fluctuations in internal flow or extreme abrupt pressure rise. These oscillations might lead to combustion instabilities in ramjet engines. Authors investigated a reduction system of the shock oscillation which using porous cavity and rods even under off-design condition.
In this experiment, we investigated four cases. That is (1) solid wall, (2) porous wall attached on lower wall, (3) three rods aligned spanwise, (4) three rods aligned streamwise. In the test section, the upper and the lower wall diverge at 1 degree and designated Mach number at the inlet is 2.2. This experiment was carried out by visualizing the flow field using Schlieren technique. The visualized flow field was captured with a digital high-speed camera. We investigated shock oscillation and effect of porous cavity and rods on the flow field using schlieren images. The pressure ratio was from 2.0 to 2.5. The interval of the pressure ratio was 0.1.
It was confirmed that amplitude of the shock oscillation is very large in the case of solid wall with no rods because of the interaction between the shock wave and the boundary layer. A large separation was seen in the schlieren images. Moreover, the amplitude of the shock oscillation became large as the pressure ratio increases. It was found that the porous cavity, three rods aligned spanwise and three rods aligned streamwise reduced amplitude of the shock oscillation. In these three cases, the large separation which was seen in solid wall was not observed. The porous cavity has an promising effect on the reduction in the amplitude of shock oscillations in three cases.
As a result, it was clear that the porous cavity and three rods aligned spanwise and streamwise have effect on the reduction of amplitude of shock oscillation.

Shock wave, Compressible flow, Porous cavity, rod

Direct numerical simulation of hydrogen–air turbulent swirling premixed flame in a cuboid combustor is conducted to investigate thermoacoustic instability and dynamic modes of turbulent swirling premixed flame in combustors. A detailed kinetic mechanism and temperature dependency of physical properties are considered in DNS. Size of the cuboid combustor is assumed to be 15.0 mm in streamwise direction and 10.0 mm by 10.0 mm cross-section. The shape of the inlet is a concentric annulus with 0.6 mm inner and 2.5 mm outer diameters. Temperature of the wall is assumed to be 700 K. Equivalence ratio, pressure and preheating temperature is set to 1.0, 0.1 MPa and 700 K, respectively. Velocity profile at the inlet is given analytically under assumption of steady, axial symmetry and no-slip boundary conditions on the wall. Mean axial velocity at the inlet is 200 m/s and the root-mean-square value of perturbation intensity is 13.2 m/s. Two swirl number cases of 0.6 and 1.2 are investigated. Large-scale helical vortical structures are generated near the inlet of combustion chamber, and a lot of fine-scale vortices emerge downstream. Flame structure is engulfed by the vortical structures and depends largely on the swirl number. Spectral analysis of pressure oscillation on walls shows that quarter-wave mode of longitudinal acoustics has the largest energy, and that characteristic oscillations are found at higher frequencies. To investigate oscillation modes of pressure and heat release rate fields, dynamic mode decomposition (DMD) is applied to DNS results. It is shown that there are differences between dominant frequencies in spectral analysis of time-series pressure data at one point of walls and DMD of time-series pressure field data. DMD of pressure field reveals that the quarter-wave mode in longitudinal acoustics has the largest energy for the case of S = 0.6. Furthermore, it is clarified that the transverse acoustic plane waves and pressure oscillations induced by large-scale vortical motions play important roles for the pressure oscillations in combustors. DMD of heat release rate field reveals that the DMD modes of pressure with high amplitude do not necessarily have coupling with fluctuations of heat release rate. To investigate thermoacoustic instability in combustors, the relations between DMD modes and Rayleigh criterion are also discussed applying DMD to mean-subtracted data of pressure and heat release rate fields.

Swirling flame, Premixed flame, Dynamic mode decomposition, Acoustics, Micro combustor

Cavitation phenomena are abundant in hydropower systems and encountered in various hydrotechnical applications. They predominantly have negative consequences to machinery operation. In the current work, we studied experimentally cavitating flows around a flat plate with semi-circular leading edge and sharp-cut end as well as a NACA0015 hydrofoil by high-speed imaging and Particle Image Velocimetry. Both foils were investigated at a series of attack angles ranging from 0 to 9 degrees with varying cavitation number. Several known types of cavitation common to both foils, but also some different patterns, were registered. At small angles of incidence (less than 3-4 degrees), cavitation on the plate begins in form of a streak array (bubble-band) whereas the one on the hydrofoil initiates as travelling bubbles. For the regimes with developed cavitation on the NACA0015 hydrofoil, the scattered and discontinuous bubble streaks branch and grow but subsequently merge into bubble clouds forming a remarkably regular lattice pattern. Once the incidence angle increased to 9 degrees, the cavitation on the hydrofoil changed to a streaky pattern like that on the plate at small attack angles, whereas the regime on the plate showed no significant changes. The time-averaged velocity and turbulence moments show that the incipience of cavitation is governed by the development of the carrier-fluid flow around the foil leading edges, but the subsequent flow pattern depends strongly on the cavitation regime displaying markedly different distributions compared to the noncavitating case. The main cavitation parameters – the maximum cavity length, the cloud cavity streamwise dimensions and the cloud shedding Strouhal number – are analyzed and presented in function of the cavitation number and the attack angle in different scaling. The measurements confirm qualitatively the trends reported in the literature, but show also some quantitative differences, notably between the two foils considered.

partial cavities; cavitation patterns; turbulent characteristics; 2D hydrofoils; high-speed imaging; PIV

Effect of surface roughness in wall turbulence is an important issue from view points of engineering fields. Even a small roughness is well known to have an influence on turbulent flows, since it breaks up viscous sub-layer and increases the fluid drag. While Moody et al. (1944) summarized the relationship between the drag and the Reynolds number for different relative roughness, i.e. “Moody’s diagram”, the definition of the relative roughness is not clear. For example, the relative roughness of sinusoidal waves with different wavelengths is unchanged when the amplitude of the waves is kept constant.
In the present study, we investigate the effect of the wavelength of a sinusoidal wavy wall surface in a fully developed turbulent channel flow by means of a particle image velocimetry (PIV) measurement. The sinusoidal wavy wall surface which is homogenous in spanwise direction is employed as the model of surface roughness. The present PIV measurement can visualize a motion of the flow near the wavy wall especially in valleys, resulting that the skin-friction drag can be directly calculated from the present PIV data.
The experimental condition is as follows. The fully developed turbulent channel flow is considered at Re=300, where the skin-friction Reynolds number Re is based on the friction velocity and the channel half height in the case of the flat surface. Two different wavelengths of the wavy wall are examined, i.e. lambda/2a=1.0, 5.0. Here, the amplitude and the wavelength of the wavy wall are denoted as lambda and a, respectively. In the case of lambda/2a=1.0, the shorting area is 1.6 x 1.6 mm^2 which corresponds 20 x 20 in wall units.
According to the velocity distribution obtained by the PIV measurement, the local skin-friction drag coefficient is determined. Since the PIV measurement result clearly shows the recirculation of the flow in the region between crests, the local skin-friction drag decreases at valleys, while it increases at the crests. In the cases of lambda/2a=1.0 and 5.0, the skin-friction drag coefficient averaged over one wavelength decreases about 30% and 60%, respectively, as compared to that of the flat surface. In consequence, the mean skin-friction drag is changed due to the wavelength even though the relative roughness is kept at constant. In the final paper, we will present more detailed discussion about the relationship among the wavelength of the wave, the flow field and the skin-friction drag.

turbulent flow, PIV measurement, wavy wall

This paper shows that there exists ununiformity in liquid film under a droplet floating on the mother phase by visualization of the film thickness. Today, separation and mixing phenomena of immiscible liquid have been studied to develop high technology of liquid control in various industrial fields. In particular, many people have studied a droplet floating on the liquid-liquid interface as the reason for taking the phenomena to be fundamental mechanics. In this study, we visualize the time-variation of the film thickness and its break-down due to the film thinning experimentally to understand the phenomenon of droplet floating. In the experiment, a tank, with cross-section 100 mm × 100 mm and height of 100 mm, was filled with two layers of immiscible liquids: a layer of water followed by a layer of oil. Then, the droplet fluid of water was extracted from a separated reservoir with a tube pump and the droplets were generated in the oil layer by a nozzle attached to the tube tip. The size of the droplets to observe is a few centimeters from a few millimeters. To record the instantaneous film break-down, we use a high speed camera at the frame-rate of about 1500 fps. The visualization was carried out with the back-light method using a white light source and a telecentric lens to grasp their shapes exactly. And also, the droplet and the film were observed with a specific wavelength light through a color filter in the transmitted light from them. By using the experimental system described above, the spatial distribution of the light intensity was observed with regards to the slight change of the film thickness. Moreover, the time-variation of interference fringe patterns corresponding to the film thickness change could be visualized on the surface of the film. In addition, the fringe patterns near the receding edge of the film were in parallel to the edge line in the break-down process. This indicates that the film thickness has ununiformity by visually capturing the interference fringe patterns corresponding to the change in the film thickness.

liquid-liquid interface, film thickness, interference fringes, break-down process, back-light method

1. Goal

A wide range of trailers with very poor aerodynamics are hauled long distances across a vast North American highway system. Our goal is to describe preliminary smoke-wire flow visualizations undertaken to learn the characteristic flow patterns over models representing a number of typical configurations. This understanding will lead to methods to improve the aerodynamic efficiency of vehicle-trailer systems. As opposed to commercial heavy tractor-trailer systems, very little flow visualization has been done on this type of light vehicle-trailer system. Most of what has been done is dated and does not represent systems currently on North American highways.

2. Methodology

To obtain a preliminary inspection of the flow streaklines, specific detailed models have been studied. These include a Ford F150 pickup truck with a cargo trailer, a Ford F350 towing a fifth wheel travel trailer (the most common private vehicle-trailer systems on western Canadian highways); and an SUV and mini-van with a cargo or travel trailer. Identically-scaled models were used with sufficiently low tunnel blockage (< 10%) to have qualitatively correct
visualizations in comparison to full-scale. Smoke-wire flow visualization experiments were done in a 0.3 m squared test section wind tunnel at a Reynolds number of 13700. Images of the smoke-wire streaklines were taken using a Nikon D1X camera, and were illuminated with either two in-house designed strobes or two GenRad Strobolumes. The experiment was controlled with a microsecond precision purpose-built timing system.

4. Results and Conclusions

Visualizations of the Ford F150 truck-utility trailer combination indicated two major flow characteristics. The first is that the flow separated from the truck would stagnate on the trailer leading face at a distance approximately two-thirds of the way up. It would then separate again from the top leading edge of the trailer creating a second separation in the vehicle-trailer system. The second conclusion was that there was a large separation on the hood of the truck. This may be due to the low Re number or lack of a moving ground-plane in our wind tunnel. It has been a goal of this preliminary visualization to determine the need for improvements to the flow rig. In the future other solutions to this will be sought, including: adding roughness to the truck leading edge, the use of suction beneath the vehicle, elevating the vehicles onto a false floor that will have a less developed boundary layer, or the addition of a moving ground plane.

smokewire streaklines, aerodynamics, flow visualization, light vehicle-trailer systems, drag reduction

Butterflies fly by combining wing flapping and gliding efficiently and have beautiful flight patterns. Moreover, the butterfly excels in rapid acceleration and turning. As a result of recent developments in micro-electro-mechanical systems, micro-air-vehicles and micro-flight robots that mimic the flight mechanisms of insects have been attracting significant attention. However, these robots were not practical. One of the reasons for this is that the flying mechanism of insects has not yet been clarified sufficiently. A number of studies on the mechanism of butterfly flight have been carried out in recent years. Moreover, a number of recent studies have examined the flow field around an insect wing. However, the dynamic behavior of the vortex formed on the insect wing and its growth process have not yet been clarified.
We have carried out a flight observation experiment involving Cynthia cardui and clarified the flapping angle, lead-lag angle, and feathering angle of the butterfly from the viewpoint of the butterfly. Based on these results, we developed a flapping fling robot without tail wings, which is similar to a real butterfly. Furthermore, we have visualized the dynamic behavior and the detailed structure of the vortices of the flapping butterfly wing under the tethered condition. We conducted a PIV measurement around the flapping butterfly wing of Cynthia cardui and Idea leuconoe and investigated the vortex structure of the wing and its dynamic behavior. A vortex ring forms over the butterfly wings when the wings flap downward to the bottom dead position and then passes through the butterfly completely. This vortex ring then grows until reaching the wake at the bottom dead position. The vortex ring is formed over the wings regardless of the type of butterfly, but its scale varies among butterflies. Moreover, we estimated the dynamic lift generated by the flapping butterfly wing using the circulation of the vortex ring. However, these results are for a flow field under the tethered condition.
The purpose of the present study is to clarify the detailed wake structure behind the free flight butterfly wing and its generation process. We conducted scanning PIV measurements around the free flight butterfly wing of Idea leuconoe. Especially, we focused on three-dimensional vortex structure behind the free flight butterfly and the dynamic behaviors of vortex rings rolled up in flapping downward and upward.

Vortex, Wing, Butterfly, Scanning PIV

The impacts of realistic roughness on the instantaneous large-scale and energetic turbulence structures contributing significantly to the first and second POD modes are experimentally studied at Reyonlds number, based on momentum thickness, of approximately 8200. The realistic roughness was replicated from the profilometry measurements of a roughened gas turbine blade damaged by deposition of fuel and foreign materials. Two-dimensional PIV measurements were performed in a turbulent boundary layer in streamwise—wall-normal planes with 4k by 2.8k, 12-bit CCD cameras over a field of view of about 1.3 delta by 1 delta where delta is the boundary layer thickness. Different from past studies of roughness effects on turbulence structures using reconstructed velocity fields from truncated POD modes, this study looks at the instantaneous turbulence structures which are the major contributors to the first two POD modes. The effects of the studied realistic roughness on the characteristics of these energy-dominating structures are investigated, together with various one- and two-point turbulence statistics without these structures.

Turbulence strucutres, realistic roughness, turbulent boundary layer

The presented investigation aims at a better understanding of the smoke propagation behavior close to a fire in a vehicle tunnel. A longitudinal flow, representing the emergency ventilation, arrests the smoke gases close to the source of the fire. In case of undercritical ventilation, however, the so-called backlayering occurs, i.e. the buoyancy-driven upper smoke layers propagate upstream. This phenomenon is investigated in the reduced-scale, hot-gas tunnel at ETH Zürich where the fire is modeled by a hot-gas jet. The focus is on the identification of the upstream region contaminated by smoke based on the determination of the backlayering length.

A rapid monitoring of flow temperature distribution close to the tunnel ceiling is required, and suitably prepared thermochromic liquid crystal (TLC) foils were developed to provide this information. The visible TLC response is preferable to other surface imaging techniques, in particular infrared thermography, because their sensitivity to the slow thermal signature of the hot walls can be reduced. To achieve this effect, the foils are fixed to the ceiling using a structured adhesive tape, creating a small, thermally insulating gap.

A TLC foil produces a color change only across a limited temperature range of a few degrees Celsius, acting essentially as a spatial edge detector in the backlayering zone, where the temperature rise can be significantly higher.

Images recorded with a monochrome camera are thus sufficient to extract the temperature boundary information from the grey level contrast. In addition, a reference image is recorded while the hot gas tunnel is at ambient temperature. Subtracting this image from the measurement images helps to enhance the processing sensitivity while maintaining the real-time analysis capability.

Nevertheless, more detailed information on the temperature distribution is obtainable through the simultaneous use of several TLC foils with different temperature indication ranges.
The TLC technique allows the measurement of the temperature distributions in the hot-gas layers close to the walls and the ceiling. For a complete description of the backlayering phenomenon, the thermal boundary conditions at the ceiling have to be known as well. For this, heat transfer sensors are employed to measure the local heat losses which may contribute to the destabilization of the backlayering region.

Finally, a fast wire mesh sensor consisting of a matrix of resistance temperature detectors is also available in the tunnel, providing spatially resolved information on the temperature distributions in a cross section of the tunnel.

tunnel smoke backlayering temperature measurements thermochromic liquid crystals

So called “the ground effect” for a moving object in stationary fluids above/on a stationary ground surface or for stationary object above/on a moving wall together with mainstream is an typical interesting topic from both theoretical and practical points of view.
In general, wind tunnels are useful tools, when we investigate the flows at high Reynols numbers. And, the ground effect often is not negligible in the aerodynamic characteristics of various scaled models at high Reynolds numbers. Wind-tunnel experiments become the most effective approaches for these high-Reynols-number ground-effect problems to achieve precise aerodynamic measurement, once we introduce a moving-belt system in the wind tunnel.　So, the moving-belt system has progressively become important for accurate simulations of the ground effect in wind tunnels.
Recently, we have developed a moving-belt system for fundamental and accurate wind-tunnel experiments concerning the ground effect, and shown its basic performance such as the profiles of time-mean flow velocity and turbulence intensity above the moving belt of the system using a hot-wire anemometer (hereinsater, refered to as HWA). And, in order to show the effectivity of the moving-belt system, we have evaluated the aerodynamic characteristics of a track runner in solo running. Furthermore, we have investigated the air resistance of two runners in duet running with various tandem-running formations.
In the present study, we deal with one of the most fundamental and common topics related with the ground effect: that is, a sliding flat plate (or thin aerowing) just above the stationary ground surface. Specifically speaking, by using the developed moving-belt system, we investigate the ground effect in such the most simple model. Namely, we put a two-dimensional thin flat plate above the belt in a wind-tunnel test section, and conduct flow visualisations with particle-image-velocimetry (hereafter, refered as PIV) analyses, together with flow-velocity measurements using a HWA. As a result, We have confirmed that, above the moving belt, the symmetry in the alternating vortex streer past the flat plate seems to be broken, due to the existence of an the moving wall below the flat plate.

Wind Tunnel, Moving Belt, Ground Effect, Aerodynamics, Boundary Layer, Visualization

Bubble column reactors are used as multiphase flow reactors in chemical, bio reaction and petrochemical industries such as absorption and stripping. In this study, bubble behavior in two viscous fluids under uniform gas has been simulated by using a set in two-phase bubbly flow. The two-phase bubbly flow considered to be homogenous and heterogeneous. Deformation of the bubble was considered due to gas flow pressure induced from the external applied air compressor. Studies are in a cylindrical glass column with 0.095m inner diameter and 2m height. The column is equipped with one sparger in bottom, a perforated plate and various viscous liquid heights. In this study, liquid phase and gas phase were silicon oil, water and air. A high speed camera bubble behavior was visualized. Using these images enables us to calculate the Void fraction, usg and bubble size and effect of gas pressure through the column in different gas velocity, then analysed using some analysis techniques such as Probability Density Functions (PDF), auto correlation, Power Spectrum Density (PSD). The results showed that with increasing the superficial gas velocity, the frequency of bubbles and void fraction increases. It is also found that the superficial gas velocity observed is due to the different bubble rising regimes. Bubble shape with increasing the air flow varied from a laminar flow (bubble cap) to a turbulent flow. To measuring the void fraction swelling level method is used.

Bubble Column,Void Fraction, Probability Density Function, High Speed Camera.

The work presents an experimental study of a novel spin coating technique, designed to overcome the problem of partially coating, particularly with large sized wafers. The feature of this novel spin coating process is with the use of a prewetting thin film. The wafer is prewetted with solvent as it is accelerated to a predetermined rotational speed. The prewetting solvent is then cut off, and the wafer continues rotating to create a constant and uniform liquid film. Next the wafer is accelerated to another rotational speed, and liquid with relatively high viscosity is dispensed concurrently with the historical images of the liquid front on the wafer. Comparing historical images of the prewetting substrate spin-coating with the dry substrate spin-coating via flow visualization technology, demonstrates that prewetting spin-coating tends to shorten the fingering instabilities and increase the maximum fully coated radius. Since both the dispensed volume and rotational speed of the wafer are fixed, the prewetting spin coating easily achieves full coverage. The prewetting spin coating decreases the rotational speed of the wafer, thus preventing the wind shear effect, provided the volume dispensed is fixed. Meanwhile a relatively low for the prewetting liquid expands, the maximum fully coated radius.

Prewetting spin coating, Fingering instabilities, Flow visualization

Nowadays various type of moving ball is used in sports. For example, in football games, many non-rotating curved balls are used recently. These kinds of balls make it hard for the defender to forecast the direction of the ball. These moving ball impact on the outcome of the game. Therefore, the investigation on the aerodynamic force of these balls are very important for quality of the game, players and more fun. There are many researches on aerodynamics characteristics of various moving ball. However, the flow characteristics of a moving ball are still unknown especially on surface structure.
In this paper, the effect of the surface structure of ball with rotation or without rotation to the aerodynamics characteristics of the ball is investigated by using wind tunnel experiment and flow visualization. Six kinds of soccer balls (32panels, JABULANI, TANGO12, FINALE, MC5-PRO, MC500-PR) are used in this experiment. For the aerodynamics characteristics, wind tunnel is used to measure the drag and lift force of rotating and non-rotating soccer balls and the Reynolds number of this experiment is between 100000 and 500000. As the result, in case of changing the angle of a soccer ball without the rotation, the drag and lift coefficient of the soccer ball with many panels show no significant difference. However, the panel shape and panel number affects the drag coefficient transition region. The drag coefficient of MC5-PRO and MC500-PR shows a different in critical region. These balls have similar panel shape but panel number are different. For the soccer ball with fewer panel number, the critical region of drag coefficient changes with the angles of the ball and the lift coefficient is also affected by the angles of the balls.

Ball, Drag coefficient, Lift coefficient, Surface structure

Flow visualizations have been carried out to evaluate thermal performance of asymmetric micro pulsating heat pipes(MPHP). In the present MPHP, a transparent acrylic plate was attached to the stainless steel plate on which 16 parallel rectangular channels with cross-section of 1.0 × 0.5 mm2 and 0.5 × 0.5 mm2 alternately were formed. The whole size of the MPHP is 42 × 21.5 × 10 mm3. FC-72 was used as a working fluid that is well known for the high efficiency of refrigerant. During the start-up period, the amount of heating input power plays a key role in the successful operation of MPHP, thus, experiments were performed under 1~10 W of heating input power by varying the other significant factors such as filling ratios and inclination angles. A high speed data acquisition system was used to detect the start-up and steady thermal oscillation of the MPHP. High resolution infrared camera was used to investigate the temperature distribution of working fluid in the channel. The experimental results show that the vertical orientation was better than the horizontal orientation due to the gravity force acting as a hydraulic circulating force at evaporator section. Some of the result shows that the bubble generated in evaporator tends to flow toward the wide flow-path and this behavior was contributed to the driving and restoring forces for fluid circulation.

heat transfer, asymmetric pulsating heat pipe, thermal oscillation, Infrared thermography

A review is presented to conclude the recent developments in the active control of flow around a bluff body. The plasma actuator and synthetic jet are two novel active flow control techniques that have drawn extensive attentions and have been applied in various fields. One of the subjects is to control the flow around a bluff body and numerous papers have been published. In most of these studies, the plasma actuator or synthetic jet was placed near the separation point, aiming at delaying flow separation and reducing drag. Recently, a series of experimental investigations have been conducted to pay particular attention to the variations in the vortex shedding modes. It was found that some interesting control results might occur when the synthetic jet was placed at either the front stagnation point or the rear stagnation point of a circular cylinder. When the synthetic jet was placed at the front stagnation point, it was found that the wake vortex shedding patterns were classified into six regimes: antisymmetric Karman vortex mode, bistable state I, symmetric mode, bistable state II, antisymmetric mode with shortened vortex formation length, vortex generation close to the rear stagnation point. When the synthetic jet was placed at the rear stagnation point, the vortex shedding modes were categorized into three groups: antisymmetric Karman vortex mode, vortex synchronization with shedding mode varying between the symmetric and antisymmetric ones, and vortex synchronization with symmetric shedding mode. It was suggested that the papers reviewed here provided a novel and effective way for the bluff body wake control, and constituted a potential way to reduce the vortex induced vibration.

flow control, plasma actuator, synthetic jet, bluff body, vortex shedding mode

In order to visualize and investigate the gas reconfiguration in bronchioles of mankind lung, under the drive of both conventional HFOV and the HFOV with steepening respiration, a numerical simulation which included specific branches of lung has been implemented for analysis in the software named Star-ccm+. In detail, at first, a cluster model of lung bifurcations between the 18th and 20th generation has been built according to the Weibel model, and an interface was located in the 18th generation to distinguish fresh air and used air. As well as other boundary conditions, 4 different respiration patterns consisted of sinusoidal pattern as present HFOV, steepening inspiration, steepening expiration and steepening inspiration&expiration were set for simulation and comparison. Secondly, for the frequency of 10 Hz and in 3 cycles, deformations of the interface were acquired after calculation for these 4 respiration patterns at maximum volume of inhalation. Additionally, together with particle trajectories, configurations of the interface at the instant of 0.3 second were obtained after computation. As expected before, the steepening-respiration patterns manifested better intrusion effect and more exchange volume than sinusoidal ventilation. Thirdly, the exchanged air volumes in unit time were acquired at the respiration frequency of 10 Hz, 15 Hz and 20 Hz with the corresponding tidal volumes respectively. Moreover, the exchanged air volumes were calculated according to these ventilation frequencies under the steepening-inspiration&expiration pattern.

HFOV, Steepening Wave, Human Lung, Gas Reconfiguration, Simulation

The reduction of pollutant emission requires a complete understanding of the combustion process in liquid fueled internal combustion engines. The fuel injection is a key factor, as it determines the drop size distribution, which influences the liquid evaporation rate and the fuel-air mixture efficiency in the chamber. Even if the general trend in Diesel applications is to increase the injection pressure and to decrease the orifice diameter, as these two parameters seem to improve engine efficiency, the spray break up is not yet fully understood. The main reason is that the form and distribution of liquid structures in the spray is the result of a lot of interdependent and complex processes (hydrodynamic instability, cavitation, turbulence, etc.), which complicate analysis of atomization phenomena and frustrate direct control of the spray formation. Significant progresses have been recently made for the numerical simulation of injection. Direct numerical simulation (DNS) can now produce realistic results. Nevertheless, it is necessary to move beyond the simple visual comparison to more quantitative validation.

The objective of this paper is to quantitatively compare experimental and numerical observations by applying the same tools on the numerical simulations and on experimental images. The quantities used for the comparison are: liquid flow velocity, atomization progress and deformation of the liquid/gas interface. From the experimental point of view, these quantities are obtained from to a large set of images, to extract statistically valid trends. The sprays used in this work were produced by a single-hole, plain orifice injector assembly dispersing fuel oil into ambient atmospheric conditions. The velocity data and shadow images of the diesel spray used in the analysis were obtained using high-resolution ultrafast shadow imaging (USI), which provides high-resolution visualization of the spray edges and droplets, resolved within a narrow depth-of-field, limited by the collection optics.

The experimental results are confronted with DNS computations of a similar liquid jet. A coupled Volume Of Fluid/ Level Set (VOF/LS) is used for interface tracking. The incompressible Navier-Stokes equations are solved following a projection method and coupled to a transport equation for the level-set function on a Cartesian meshing. In order to provide the characteristics of the flow at the nozzle orifice for DNS computations, the internal flow was computed using a commercial CFD code (Fluent 6.3), based on the geometry deduced from X-ray imaging of the nozzle used in the experiments. The results of the numerical simulations are transformed into images by plane projection.

Finally, comparisons between experimental results and numerical simulations lead to contrasting conclusions. Some jet features are well reproduced by the computations. Improvement of DNS is nevertheless expected to fully mimic the jet behavior.

atomization, Diesel spray, experimental analysis, direct numerical simulation

A new principle of flow rectification for hybrid synthetic jet actuators (HSJAs) is introduced in this paper. The flow rectification can be accomplished by means of fluidic diodes, which are embedded in HSJAs. The novelty of the present study consists in proposal of the fluidic diode in form of conical nozzle placed against a wall. The periodic jet flow issuing from the nozzle impinges on the wall and thus the flow differences during blowing and suction strokes result in enhanced rectification effect. The effect is quantified using so called volumetric efficiency. The volumetric efficiency was evaluated experimentally in this study. The experiments were performed using constant temperature anemometry and smoke visualization technique in phase-locked arrangement with air as working fluid. The nozzle-to-wall distance and driving frequency of present HSJA were varied and the combination of the parameters achieving the highest volumetric efficiency was found.

hybrid synthetic jet, hybrid synthetic jet actuator, volumetric efficiency

A method of researching optically inhomogeneous mediums is the method of the laser refractography [1]. It is based on the phenomenon of refraction of structured laser radiation in optically inhomogeneous media and registration of its deviation’s angle with the digital video camera and computer processing.
Caustics are special lines and special surfaces near which the intensity of the light field increases sharply. Real laser beams have the finite sizes that can lead to occurrence of caustics and incorrect results of measurements. That is why it is so important to know the area of caustics’ occurrence that allows optimizing experiments.
The first inhomogeneous medium, which are considered from the viewpoint of caustics’ formation, is the diffusive layer in liquid appears near interface of two liquid mediums with various physical characteristics [2]. In this work liquids with various refraction indexes will be considered. Refraction index of more solid liquid is n1, less solid – n2 (n1>n2). The model of diffusive layer we will describe with special exponential model.
The second medium is spherically inhomogeneous medium. Two cases of caustics’ emergence are considered: spherically symmetric temperature field of a hot ball in cold water and temperature field of a cold ball in hot water.
For these models of inhomogeneity computer simulation of 3D-visualisarion’s dynamics of laser rays’ refraction is presented in this work. It is shown how can change position and shape of caustic’s surface by variation different parameters such as angle of refractogram’s incidence, gradient of refraction index, etc. Also experimental 3D-visualisation’s dynamics was performed and it is possible to receive evidence that experimental and calculation parameters have good compliance.
For reconstructing the values of refractive index under conditions of strong refraction a method was developed [3], which is based on the visualization of ray trajectories inside an optically inhomogeneous medium. Computer simulation of caustics and ray trajectories allows get solution of the inverse problem of refraction based on the experimental caustics visualization.

References:
1. Rinkevichyus B S, Evtikhieva O A, Raskovskaya I L. Laser Refractography. New York: Springer, 2011.P.189.
2. Vedyashkina A.V. Computer modeling of optical rays’ refraction in inhomogeneous mediums. // Journal of Beijing Institute of Technology. 2013, Vol.22, Suppl.1, Pp.71-76.
3. Raskovskaya I.L. Laser refractive tomography of phase objects. // Quantum Electronics. 2013, Vol. 43 (6), Pp. 554-562.

LASER REFRACTOGRAPHY, CAUSTIC, REFRACTION'S DYNAMICS, DIFFUSIVE LAYER OF LIQUID, SPHERICALLY SYMMETRIC TEMPERATURE FIELD

Double cone geometries are typical models in supersonic and hypersonic flow. However, the flow field is so complicated that few techniques could realize the fine structures which include the shock wave interaction, shock wave boundary layer interaction and separation. In the past twenty years, a great amount of work was dedicated to hypersonic double cone flow especially at Mach>8 for CFD validation, and pressure and heat transfer distribution were measured. Little attention was paid to supersonic flow over double cone geometries. With nano-tracer planar laser scattering (NPLS) technique, fine structures of the flow field in the symmetry plane could be detected, which are of great value to CFD validation and engineering. NPLS technique has been successfully applied in the measurement of density field, velocity field and aero-optics.
Three double cone geometries of various parameters are investigated in a low-noise supersonic wind tunnel. The first cone angles are 5, 8 and 12 degree, while the second cone angle is 40 degree. Due to the strong adverse pressure gradient induced by the second cone, the boundary layer of the first cone occurs and grows in an incredible speed. To the 5-40, 8-40 and 12-40 double cones separation region and the separation shock wave near the corner could be distinguished. Around the second cone there’s shock wave interaction and transmitted shock waves. The boundary layers on the second cone have all developed into turbulent flow. 5-40 and 8-40 configurations have relatively fiercer separation. However the 12-40 configuration has a separation shock wave, for its boundary layer keeps laminar state to the end of the first cone. It could be analyzed that the lager first cone angle works as a transition section and when coming to the second cone the flow will have a smaller turn angle. More large scale vortices could be observed in the NPLS figure of the double cones with a smaller first cone angle. Numerical computations are done on the 5-40 and 12-40 configurations using the k-epsilon turbulent model and second order upwind scheme, and comparisons are made between numerical and experimental results. Numerical results are shown in the form of density contour for the grayscale grades of NPLS figures rely on the intensity of nano-particles and thus rely on the density. The numerical results in general agree well with experimental results, however the separation region sizes are both much smaller and the separation shock waves are closer to the corner than the experimental results. This difference might be caused by the unchanging viscosity considered during the simulations while the actual one changes with the variation of temperature. Fine structures of vortices could not be viewed using ordinary numerical methods.

double cone; supersonic flow visualization; NPLS

Ion wind flow has been widly studied for its advantages of micro fluid device. However, it is very difficult to predict the performance of the ion wind for various conditions because of its complicated electrohydrodynamic system. Thus, a reliable numerical modeling is required to design an otimal ion wind generator and calculate velocity of the ion wind for the proper performance. In this study,the numerical modeling of the ion wind has been modified and newly defined to calculate the veloctiy of the ion wind flow by combining three basic models such as electrostatics, electrodynamics and fluid dynamics. The model has included presence of initial space charges to calculate transfer energy between space charges and air gas molecules using a developed space charge correlation. The simulation has been performed for a symmetrical geometry of a pin to parallel plate electrode.Finally, the results of the simulation have been compared with the experimental data for the ion wind velocity to confirm the accuracy of the modified numerical modeling and to obtain the optimal design of the ion wind generator.

Ion wind, Space charge, Numerical visualization, corona discharge

Three-dimensional optical tomography technique was developed to reconstruct three-dimensional flow fields using a set of two-dimensional shadowgraphic images and normal gray images. Five basis functions such as cubic B-spline, o-Moms, keys, and cosine functions and Gaussian basis functions were used to calculate the weighting coefficients for a projection matrix. Two different forms of a multiplicative algebraic reconstruction technique (MART) were also used to solve inverse problems. The reconstruction algorithm was examined by using several phantoms which included droplet behaviors and random distributions of particles in a volume. From three high speed cameras, which were positioned at an offset angle of 45° relative to one another, shape, size and location of electrohydrodynamic jets with respect to the nozzle position were analyzed using shadowgraphic tomography employing a multiplicative algebraic reconstruction technique (MART). Additionally, a flow field inside cone-shaped liquid (Taylor cone) which was induced under electric field was also observed using a simultaneous tomographic reconstruction technique for evaluating intensities of particle light and combining with a three-dimensional cross-correlation. Various velocity fields of a circulating flow inside the pendant droplet and cone-shaped liquid from the electrohydrodynamic jetting due to different physico-chemical properties of liquid and applied voltages were also investigated by the tomographic particle image velocimetry (Tomo-PIV).

Optical tomography, Basis function, Shadowgraphic, Electrohydrodynamic jet, PIV

Electrohydrodynamic (EHD) ink jet has been applied to various industries such as an ink-jet printing, a LED monitor and a drug delivery. Thus, three-dimensional EHD jetting behavior has studied using multiple angles of view. Mostly, tomography has been used to reconstruct the EHD jet, however it takes relatively long time to analyze the alteration of meniscus. Therefore, shadowgraphic multiplicative line of sight method (SMLOS) was suggested in this study to reconstruct real time and asymmetric jetting behaviors. The image obtained from the EHD jetting at each particular angle was modified to the shadowgraphic image matrix using the difference of the light intensity between the shape and background, and it was related to other shadowgraphic image matrixes obtained from other angles since each pixel of the image matrix has an inherent point in the three-dimensional axis. To verify a faster speed of the reconstruction for the SMLOS, synthetic phantoms were used. Three shadowgraphic images were created by the phantoms and the jetting behaviors were reconstructed by the SMLOS and the tomography method using a multiplicative algebraic reconstruction technique (MART) with a cubic cosine basis function. Consequently, the increased speed of the reconstruction and the improved reconstruction quality for the SMLOS were confirmed by the numerical analysis and the experiment using multiple cameras for the EHD jetting behavior.

electrohydrodynamic(EHD), multiplicative line of sight, shadowgraphic, real time

A food bolus is digested and absorbed as it travels through the mouth, pharynx, esophagus, stomach, and small and large bowels. The esophagus transfers the bolus by peristalsis. The organs below the esophagus transfer and agitate the bolus through peristalsis, segmentation, and pendular movements (mechanical digestion). Mechanical digestion is slow; for example, peristalsis happens 4–5 times/min in the stomach, and 7–8 times/min in the small bowel. No technique developed thus far has allowed for the visualization of pharyngeal motion. The process involved is complex and rapid and ends within 1 s. The structure of the pharynx differs from the cylindrical shapes of other involved organs. The pharynx bifurcates at the mouth and nose and again at the larynx and esophagus. The pharynx has longitudinal muscle internally and circular muscle externally. These differences suggest the use of various types of muscular action for bolus transport through the pharynx. Traditional methods have been of limited use in characterizing the muscular movement involved.
The authors have developed a numerical swallowing simulator (Swallow Vision®), which uses medical images to reconstruct the biomechanics of swallowing. This study will report the pharyngeal motion during swallowing as suggested from the visualization of bolus travel.
The Swallow Vision® reconstruction was based on computed tomography (CT) images and the video-fluorography results from a 25-year-old healthy male volunteer. Bolus flow was simulated using the moving particle simulation (MPS) method (Particleworks®, Prometech Software Inc.), which is a meshless method. The results confirmed the validity of Swallow Vision®. We obtained cross-sectional views of the pharynx and bolus throughout swallowing. These images showed that the pharynx shortened and contorted to assume a crescent-like shape. The upper entrance to the cavity was fully closed by the tongue base, with an opening remaining below the epiglottis. The bolus remained intact, leaving behind minimal residue.
The Swallow Vision® numerical simulator indicated that the pharynx constricted from the superior to the inferior end, shortening itself toward the soft palate. Peristalsis involves alternating periods of constriction and shortening, while segmentation involves constriction alone. The use of two complementary patterns of muscle activity differentiates the pharynx from other organs.

Swallowing, Pharyngeal motion, Visualization, Circular muscle, Longitudinal muscle

Testing of optical inhomogeneities by the Talbot-images method is based on the analysis of the distortions in the self-images of two-dimensional periodic objects. The aim of this work is to adapt the technique for measurements in flames. This paper discusses the principles of the Talbot-images method and optical scheme for the diagnostic of reactive gas flows. The experimental study was performed for premixed methane-air flame formed by an axially symmetric nozzle. The deflection angles of the probe radiation were determined from measurements of the relative displacements in the spatial structure of the Talbot-image. The Abel integral equation was solved to restore the refractive index distribution in the flame. Calculation of the temperature field in the reacting flow was based on the assumption that the refractive index of the flame differs slightly from the refractive index of the ambient air heated to the same temperature. Inaccuracy of the calculations was evaluated by comparing the results with the thermocouple measurements. The results demonstrate that the Talbot-images method can be used to measure the temperature distribution in the reacting gas flows with high spatial resolution.

methane-air flame, temperature, Talbot effect, Talbot-images method

Because the swallowing action of human beings is very fast and complex, it is difficult to understand the relationship between the movement and function of each organ during swallowing. Moreover, the information provided by modern medical images of swallowing is usually fragmentary and insufficient to obtain changes in the physical properties of a food bolus.
The aim of the present study was to correlate the movement of human organs and bolus flow configuration, including changes in the bolus’s physical properties, using “Swallow Vision®,” a 3-dimensional human swallowing simulator.
Swallow Vision® was developed through the use of realistic human organ models and the meshless 3-dimentional moving particle simulation (MPS) method (Particleworks®, Prometech Software Inc.). The human organ model used to create Swallow Vision® was reconstructed using CT images and video-fluorography images from a 25-year-old healthy male volunteer. The quantitative and qualitative accuracy of bolus flow configuration and organ movement as depicted by Swallow Vision® have previously been validated. Swallow Vision® could visualize changes of food bolus configuration to be presented as a 4-dimensional movie with real-time changes in perspective (3D AVS Player, CYBERNET Inc.).
The numerical experiment was performed by comparing bolus flow configuration with the movement of water (Newtonian) and thickener (non-Newtonian) fluid models. The extracted values as well as visual observations during the simulation confirmed that the shear rate distribution of the thickener model was much narrower than that of the water model, and the liquid bolus of the thickener model flowed into the pharynx with less particle splash. The quantitative and qualitative results of the thickener model simulation showed that despite the high viscosity of the liquid bolus at the center of the tongue, the level of viscosity decreased rapidly in the area of transition from the back of the tongue to the root of the tongue. From the eppiglottis to the esophagus, the viscosity of the food bolus was much lower than other region owing to the increased shear rate and flow ability progressed in this region.
The numerical visualization possible with Swallow Vision® correlated with the complex movement of human organs as well as bolus flow configuration, including the associated changes in physical properties. In particular, the information related to changes in viscosity during swallowing will be helpful in identifying the appropriate diet for people with swallowing difficulties or dysphagia.

Moving particle simulation method (MPS), Swallowing, Numerical simulation, Liquid bolus, Shear rate, Visualization, Non-Newtonian fluid, Viscosity, 4–dimensional movie

Mis-swallowing can be classified as one of several patterns based on the associated clinical symptoms. Because of ethical and safety reasons it is difficult to estimate the risk of mis-swallowing for each patient and each food with classified mis-swallowing patterns.
The purpose of this study was to investigate the influence of physical properties of a food bolus and organ movement for swallowing.
The original “Swallow Vision®” simulation was based on the 3-dimensional moving particle simulation (MPS) method (Prometech Software Inc.) as well as a realistic human organ model that included information related to organ configuration and movement. The human organ model used to create Swallow Vision® was reconstructed with CT images and video-fluorography images of a 25-year-old healthy male volunteer. The qualitative and quantitative accuracy of bolus flow configuration and organ movement as depicted by Swallow Vision® have previously been validated. Swallow Vision® can be used to visualize food bolus configuration numerically as a 4-dimensional movie with real-time changes in perspective (Micro AVS, CYBERNET Inc.).
Swallow Vision® has allowed for numerical comparisons using a standard human model based on normal water-swallowing as well as three different food-bolus models (low-viscosity, standard-viscosity and high-viscosity models).　Mis-swallowing could not be confirmed in the case of a food bolus model with standard viscosity (based on water). By visualizing the numerical simulations of low- and high-viscosity food models, we were able to characterize mis-swallowing patterns as “aspiration before and after swallow” or “aspiration after swallow,” respectively. These patterns correspond with the system of classification based on clinical experience. This result indicates that the standard human model created using Swallow Vision® was based on normal water swallowing and has validity only in relation to the standard viscosity model (water). These numerical experiment results show that normal and healthy human beings unconsciously adjust organ movement according to a particular food’s properties. The improper execution of these adjustments results in mis-swallowing.
Based on the results presented here, we conclude that Swallow Vision® is a useful tool for investigating the relationship between human organ movement and food bolus properties.

Mis-swallowing, Moving particle simulation method (MPS), Numerical simulation, Visualization, Viscosity, 4–dimensional movie

Conventional shadowgraph and schlieren photograhy with "Z" type provide density information along an integrated path are widely used to show the wave configuaration qualitatively. The focusing schlieren method can focus on a certain region and can mainly show the density information of the region, other region information can be record as a uniform background, so the focusing schlieren method can be used to show the complicated and a three-dimensonal flow, the density value can be obtained from the schlieren images. The focusing schlieren system with a 150mm testing field in diameter has been set up in China Aerodynamics Research and Development Center, its least depth of sharp focus is 20mm, the system has been used in 0.6m shock wind tunnel and combustion wind tunnel, the flow density, boundary layer have been obtained in the wind tunnel. The multi-plane flow visualization has also been developed by the syetem. The application results of focusing schlieren syetem in the wind tunnels are also introduced.

focusing schlieren, flow visualization, density measurement, wind tunnel, schlieren photography

Development and Characterization of a Pressure-Sensitive Luminescent Thin Coating Based on Pt(II)-Porphyrin Self-Assembled Monolayers.

by Y. Sakamura, T. Suzuki and S. Kawabata

Introduction
Pressure-sensitive paint (PSP) technique has been widely acknowledged as a valuable tool to visualize surface pressure distributions with high spatial resolution. One of the most prominent features of the PSP technique is that pressure probes (i.e., photoluminescent dyes) are extremely small compared with those of other conventional pressure measurement tools. Therefore,the PSP has been expected to be used for pressure measurements in microscale flow devices such as micro total analysis system. In the present work, we have developed a pressure-sensitive luminescent thin coating (PSLC) applicable to the visualisation of pressure distribution in microscale flow devices by the self-assembled monolayer (SAM) process. The absorption spectrum, and pressure and temperature sensitivities of the PSLC have been then measured to characterise the PSLC.

Experiments
The photoluminescent dye, Pt(II) tetra[3-(penta fluoro phenoxysuccinyl-oxyethoxy)phenyl]-porphyrin (PtTPFPSOPP), was synthesized and then chemisorbed on indium tin oxide (ITO) glass by SAM process to develop PSLC samples. The ultraviolet-visible (UV-vis) absorption spectrum of the developed PSLC was measured and compared with that of the porphyrin dissolved in dichloromethane. Pressure and temperature sensitivities of the PSLC were measured in a pressure-and-temperature-variable chamber of Institute of Aeronautical Technology, Japan Aerospace Exploration Agency (JAXA).

Results
The UV-vis absorption spectrum of the PSLC showed the Soret band (centered at about 400 nm) and Q band (centered at about 510 nm) similar to those of porphyrin dissolved in dichloromethane. This fact indicates that the photo luminescent properties of the porphyrins covanlently attached to the surface of ITO glass are retained. It was found that the luminescent intensity of the PSLC decreased by 20 % against the pressure change from 0 to 1 atm at 20 degrees Celsius, and linearly decreased by 0.7 % per kelvin against the temperature change from 0 to 60 degrees Celsius at 1 atm.

Conclusion
A pressure-sensitive luminescent thin coating has been newly developed by SAM process in the present work. The luminescent thin coating was found to be applicable to the visualisation of pressure distribution in microscale flow devices.

PSP,Pressure measurement, SAM, Porphyrin

A water mass in the ocean is a large body of water in a region that has relatively homogeneous characteristics, which are clearly different from the surrounding water. Water masses flow dynamically and have interannual variability, hence the distribution can change dramatically even over short time periods and may differ from year to year. The distribution of water masses has become one of the most important topics in recent oceanic research because it is closely related to fisheries, and many oceanic phenomenons.

Many traditional studies have focused on visualizing the static distribution of water masses using the observed ocean data. However, this type of visualization cannot show the dynamic flow for the low temporal and spatial resolution of the observed data. Furthermore, the traditional approach always classifies different water masses based on a unique definition. This can be not accurate because the interannual variability may cause the definition of water masses to change every year. Hence, adjustments need to be made by ocean specialists to extract the correct distribution, even though these adjustments from different ocean specialists can be different.

In this paper, we use a multi-variate high-resolution ocean dataset from the northwestern Pacific Ocean near Japan to visualize the details of the water mass. The dataset is simulated at a high temporal scale to provide detailed information about the dynamics of the water mass. To extract the distribution of the water mass from the simulated ocean dataset, we develop a multi-variate visualization system that allows us to investigate the time-varying distributions of the water mass after adjustments are made by the ocean specialists. Such adjustments are important because directly applying the existing definition to extract the water mass would result in incorrect rendering results. However, different ocean specialists may have different perspectives on the distribution of water masses. As a result, we generate an ensemble-averaged visualization based on the adjusted rendering results that provides a more authentic rendering of the distribution of the water mass. In the experiments, we first show the interannual variability of the significant water mass and then visualize the dynamic behavior for the period of interest in different years. We also highlight a mixing phenomenon that has a strong influence on the distribution of the water mass. We can obtain a clear visualization of the interannual variability of water mass dynamics.

Oceanography, water mass, large data, visualization

In order to observe the transient behavior of N2O/C2H5OH spray ignition in a subscale thruster, the ignition flow field was visualized by a shadowgraph technique. The inner diameter of a combustion chamber was 22 mm, and total mass flow rate was about 16 g/s for a combustion pressure of 9 bar. The combustor equipped a shear coaxial injector, which injected liquid ethanol from the center round hole, and N2O from the annular gap. The shadowgraph of ignition flow field was recorded with high speed CCD camera, a high power LED, and two plano-convex lenses. The pressure data, which were measured at10 kHz sampling rate, showed abnormal rises of oxidizer injection pressure and misfiring traces of combustion pressure at the moment of ignition. As a result of shadowgraph image analysis, we found that there was reverse flow of flame and fuel due to the low pressure drop at the gas injector, and it caused the combustion in the gas injector and flame quenching.

Combustion, Transient phenomena, Reactive flows, Shadowgraph, Ignition, Nitrous Oxide

The present study proposes a new three-dimensional (3D) three-component (3C) technique for velocity measurement based on tomographic stereo PIV (TSPIV). Unlike the convectional TomoPIV, this TSPIV consists of three data-reduction steps: the 3D reconstruction of light intensity fields, the stereo projection, and the standard stereo PIV analysis based on 2D cross-correlation and stereo reconstruction. As a result, the proposed TSPIV can provide 3D3C velocity information quite efficiently in the well-established framework of stereo PIV technique.
The 3D reconstruction is done by the use of the MART algorithm coded for GPU. The stereo projection (1) extracts a layer of interest from the reconstructed 3D light intensity field and (2) projects the light intensity in the layer to each camera view to prepare the projected particle images for stereo PIV analysis. The projected particle images are finally analyzed with the standard stereo PIV technique. The process from the stereo projection to the stereo PIV analysis is repeated for any desired layer within the reconstructed 3D light intensity field.
The proposed TSPIV outperforms the conventional TomoPIV in terms of the data-reduction time. This is because the standard stereo PIV is remarkably more efficient than the standard 3D cross-correlation method employed in the TomoPIV. The measured speed-up of the data processing was about 60 times.
The proposed technique was carefully examined though the numerical simulation using synthetic images with respect to the velocity measurement accuracy. The synthetic images are produced based on the complex 3D laminar flow in the T-channel (referred as the engulfment flow), where that velocity field is obtained through the finite-volume numerical simulation. The synthetic assessment showed that the TSPIV has the same accuracy as the conventional TomoPIV.

Keywords: 3D PIV, tomography, stereo reconstruction, cross-correlation, synthetic assessment

The fluidic watering device has a simple structure without any moving part. There is no friction and is no abrasion, and only self-oscillating phenomenon is applied. They are the strong points of this device. The jet of this device is controlled only by a circular vortex chamber, and self-oscillation occurs by pressure difference of the left and right parts of the vortex chamber. By the momentum balance of main jet, the time required for reaching the critical pressure is calculated and decided the oscillating frequency.
The fluidic watering device is applying to melt snow on the railway track of Sinkansen. This time the fluidic device was used for the watering device to the agriculture.
This watering device was designed and made by the following items. The watering angle of this device is 120°, the supply pressure is 0.3MPa, the flow rate is 8 l/min and watering distance is 8 m.
The device of manufacture for this trial is made of hard plastic. So, the weight is very small as 60gf.
From the results of watering test, it is conformed that this device acts smoothly as the main specifications.
It is made clear that by receiving the driving force combining of the watering devices, the watering is possible on the condition of rotating.
Moreover, in the case of watering the agricultural chemicals by this device, this device makes particulates, not makes fogs. So, there is no dangerous to absorb the chemicals.
From above mention, it became clear that this device can use as watering device for agriculture.

Fluidics, Vortex chamber, Oscillation device, Watering device, Agriculture.

Fluid convection is one of the basic physical phenomena under consideration of the formation of nanoparticles by the hydrothermal synthesis. Arising as the result of the uneven heating convection flows determine the behavior of the system and the efficiency of hydrothermal synthesis, which is determined by the temperature field. For getting specified performance during hydrothermal synthesis of nanoparticles is necessary to study emerging convection flows that determine the results of the process.
In this paper as a method for studying the convective fluid flow in a model object that emulate the process of hydrothermal synthesis method used digital holographic interferometry. Advantages of the chosen method are the ability to monitor the results in situ and fast data processing using a computer.
To visualize the convective flows in the model object when it is heated is used the device which developed by authors. This device allows evaluating the change of temperature fields in the samples during the experiment.
Mathematical modeling of convection fluids with different configurations of the heat source in the conditions of a temperature gradient up to several tens of degrees was done. The model includes a description of the macroscopic (measured in the experiment) and microscopic (theoretically estimated) parameters. The algorithm of numerical solution of the Navier-Stokes and thermal conductivity equations was builded. Obtained results for the temperature fields at various modes of heating source and for liquids with different viscosities. Results of experimental and numerical calculation qualitatively identical.

heat transfer, free convection, digital interferometry, flow visualization, hydrothermal synthesis.

Pressure-sensitive paint (PSP) is an optical pressure sensor based on oxygen quenching of its luminescence; the luminescence intensity varies with a variation in oxygen concentration, or pressure. In general, the luminescence intensity also varies with temperature. Therefore, it is important for a precise pressure measurement to measure PSP temperature and correct the temperature effect on the PSP result.
Temperature-sensitive paint (TSP) is widely used as a temperature sensor for the correction, because most of the apparatuses can be shared with the PSP measurement. Dual luminescent sensors fabricated by simply mixing PSP and TSP have been proposed, however, deterioration of sensor properties, such as photostability under an illumination, was reported in some luminophore combinations. This is caused as a result of the interaction between the PSP and TSP luminophores such as energy transfers.
We have developed a novel dual luminescent sensor to overcome above difficulty in the previous dual luminescent sensors. The newly developed sensor is composed of discrete dot arrays of PSP and TSP, which are arranged with an inkjet-printing technique. Since PSP and TSP are isolated from each other, the dual luminescent arrays sensor avoids the interaction between the PSP and TSP luminophores. It is an advantage of the dual-array sensor that preferable solvent and binding material can be adopted for each luminophore.
In this study, a 2-propanol solution of PtTFPP and a toluene solution of ZnS–AgInS2 (ZAIS) nano-particles were employed as PSP and TSP solutions, respectively. Spectral result confirmed that the dual-array sensor could prevent the interaction between PtTFPP and ZAIS that was observed in the sensor prepared from a mixture solution of PtTFPP and ZAIS. Pressure and temperature sensitivities of the dual-array sensor were comparable with conventional PSP or TSP. Moreover, the pressure distribution on the surface with a non-uniform temperature distribution was successfully measured by the dual-array sensor.

PSP, TSP, Dual luminescent sensor, Inkjet-printing

The effect of emission exposure on absorbing objects results in an increase in temperature of an object and also changes in its optical and physical characteristics. In studying low absorbing objects in the visible spectral range the more conveniently used a visible light as a probe. In this case is possible to use well-developed methods for optical diagnostics not only for the quantitative assessments, but also for the visualizations of the process.
At this paper for monitoring and visualization of phase changes of absorbing objects used a digital holographic interferometry's stand with a probe light λ=532 nm and sensing area is 50x50 mm. As study object, used samples of polymer material for volume holography in the form of discs 2-4 mm thick. The expose emission (λ=473 nm, P= 50 mW) is located in absorbing region of the sample and the exposed area is much smaller than full area of a sample. Irradiated area of the sample, absorbing the energy, bleaching and heated. Bleaching process occurs in a strictly localized area of influence of the radiation beam 473 nm. While the temperature increases by heat transfer is distributed in the unexposed areas of the sample.
The experimental technique consists in registering interferograms representing the phase portrait of the sample at a given time. Phase differences were determined by comparing the interferograms obtained at the moment with the interferogram recorded in a stable condition before the start exposure to sample. Changing the phase portrait of the sample during exposure is a set of interference fringes in form of concentric circles with center on the impacts area. These data allow estimating change of the temperature field in the sample at any time of observed effect of heat transfer.
As the result of this work showed the possibility of using digital holographic interferometry's methods for measuring the thermal effects of influence of radiation on the weakly absorbing objects, including objects with photo-induced refractive index change.

heat transfer, digital interferometry, visualization of the heating process, phase portrait

We address two important topics in computational visualization of 2D time-dependent flow: the visualization of vortices, and the visualization of the dynamics of material lines. Many, even partly contradicting, definitions have been proposed so far for the identification of vortices. Some focus on vortex centers, whereas others provide scalar indicators of vortical regions. A major aspect in all these concepts is their applicability to time-dependent flow---while early approaches were based on instantaneous concepts, more recent techniques explicitly take into account the time-dependence of the investigated fields.

Material lines represent an important tool for theoretical and practical reasoning in time-dependent flow fields. This is supported by recent advances in computational flow visualization based on streaklines, in particular in the field of time-dependent vector field topology. The dynamics of time-dependent flow is primarily accessible by means of the deformation, and intrinsic stretching and squeezing of material lines, which has given rise to various approaches in the field of time-dependent topology in terms of Lagrangian coherent structures and the regions of qualitatively similar behavior they define.

To address these topics, we employ the 3D space-time representation of time-dependent 2D vector fields, i.e., we make the underlying ordinary differential equations of particle tracing autonomous by treating time as an additional dimension. Hence, we turn the 2D time-dependent representation into a steady-state 3D vector field in which streamlines represent pathlines of the original time-dependent field. This allows us to employ any 3D streamline-based concept to the space-time representation and reinterpret its result as a pathline-based result. The advantages of this approach have already been demonstrated for vortex core lines due to Sujudi and Haimes. In this paper, we demonstrate and discuss some of the difficulties of their approach. To improve on their vortex core line method, we propose employing the space-time approach to other vortex core line criteria. Beyond that we derive also scalar indicators that are Galilean-invariant and appropriate for the analysis of time-dependent flow. In the space-time field, stream surfaces represent material lines. This eases their extraction and makes them applicable to space-time line integral convolution (LIC). By applying LIC on the space-time stream surfaces, we visualize the intrinsic dynamics of material lines, i.e., how they stretch and squeeze over time, giving insight into mixing processes, also in the context of hyperbolic trajectories, which are closely related to the topology of time-dependent vector fields.

unsteady flow, space-time visualization, vortex core line extraction, material lines

Background:
The human nasal cavity comprises of complex structures with delicate geometry and the features make it difficult to understand and to simulate the airflow within it. In vivo experiments or direct measurements within the nasal cavity are almost impossible without affecting the airflow itself. Sufficient information by in vitro experiments on this matter may lead a massive contribution in understanding its physiological process as well as in medical technology.

Objectives:
The main objective of this project is to address the relevancy of the airflow patterns between real and simplified models of the human nasal cavity in order to broaden the understanding on mechanics of nasal airflow patterns and to clarify functions of each nasal part.

Methods:
In this study, in vitro experiments were carried out using a real model of the human nasal cavity, and several types of simplified models were also adopted to interpret the flows within the complicated real model. A highly detailed 3-D nasal cavity model derived from the CT scan of a healthy adult was used for the real model. Simplified models can be divided into 2 types; (1) the most basic designs, which consist of only the nasal cavity, or that with only the middle concha and the inferior concha (2) the intermediate designs which include common meatus, and middle and inferior conchae with curves and bends. In the authors’ previous paper (FLUCOME2013), the relevancy of the airflow pattern between simplified models (1) and real models was studied. Furthermore in this research, simplified models (2) with additional parts to closely resemble real model were adopted. Experiments were carried out in Reynolds numbers Re=880 and 1530 based on the average hydraulic diameter of nares, but the difference was hardly found between results on two conditions.

Results and Conclusions:
Based on the results of simplified models, rolls of the conchae were made clear: 1) the existence of the conchae is to prevent the generation of a large whirl within the nasal cavity; 2) Regarding the length of the conchae, the longer media concha makes the flow pass the middle meatus. This flow pattern is same as in the real model. It is concluded that the conchae work as guide plates. Thus complicated flow phenomena within the real model have been comprehended with the help of simplified models.

nasal cavity, modelling, in vitro experiments, particle image velocimetry

New generation quasi-stationary plasma accelerators generate high-energy compression plasma flows of specified composition and on a set of parameters (plasma velocity 50–200 km/s, temperature and concentration of charged particles 40–200 kK and 10 16–10 18 cm–3 accordingly, discharge duration 100–500 microseconds) surpass all other available types of plasma accelerators. These plasmadynamic systems operate in the ion current transfer mode and provide the ion-drift acceleration of magnetized plasma. The interest to such plasma accelerators is connected with the solution of problems of controlled fusion (injection of a plasma in various magnetic traps, problem of the first wall of the thermonuclear reactor etc.). Also, the studies conducted have shown the high efficiency of compression plasma flow action on samples in substantial modifications to the surface microstructure and morphology, phase and structure transformations of various materials, which enhance their exploitation properties.
This report presents results of interferometric, shadowgraphic and spectroscopic studies of plasma flows generated by a magnetoplasma compressor (MPC), a two-stage quasi-stationary high-current plasma accelerator (QHPA) of P-50M type and an erosion MPC.
Among the most informative and yet extremely complicated techniques for diagnostics of plasma accelerators are interferometric and shadowgraphic methods based on visualization of optical inhomogeneities in objects under study. Due to unique features inherent in such methods, these latter provide a possibility to obtain an extensive and reliable information without adverse effects to parameters of plasma being investigated.
Using developed shadow-interferometric device the mass rate of working gas for gas-discharge MPC was measured.
The electron concentration of plasma formations in channel of both gas-discharge MPC and QHPA and in the plasma flows was determined using the laser interferometer. Plasma temperature was determined from results of experiments on a supersonic compression flow incidence on a thin wedge with an acute leading edge.
Shadow method providing a way of obtaining the electron density distribution was developed. Studying of interaction processes and measurements of electron density of opposing compression plasma flows generated by erosion MPC’s were conducted.
The spectrum analysis of the plasma emission allowed us to measure electron temperature and electron density in the collision area of plasma generated by erosion MPC’s.
Experimental estimations of basic thermodynamic parameters of plasma have shown that in the collision area of compression flows they are at least twice as high as those in a free (non-colliding) flow.

plasma, plasma accelerator, magnetoplasma compressor, optical diagnostics

We discuss in this paper focusing on the treatments of the interface between the solid and the fluid and propose a calculation method with the slip effect on the surface of a slimy material. An engineering model to express the slimy surface, which the creatures living in water such as fish or frogs have, is proposed, where the slip ratio α, which is the reduction ratio of the shear stress near a solid wall obtained through the experiment, is introduced in the shear term of the Navier-Stokes equation. The splash pattern calculated by the proposed method with Moving Particle Semi-implicit Method is in good agreement with the experimental result. The above method for calculating the splash is applied to the large scale parallel computing in 3D, which depicts the more detailed splash patterns.

Fluid Structure Interaction, Multiphysics Problems, Boundary Condition, Computing Methods, MPS method

A solution of a surfactant, Cetyltrimethylammonium bromide: CTAB, forms wormlike micelles with a counter ion, such as NaSal, and exhibits a strong viscoelastic property. It is used as a thickener and an agent of drag reduction of turbulent flow. Its flow behavior is very complex and still unclear. In this study, we force the stress fluctuation phenomenon, which occurs in the Couette flow of the wormlike micelles solution in a concentric cylinder flow cell with certain conditions. A rheometer is used as a test bench to control shear rate and measure shear stress. The flow birefringence is also observed simultaneously using a crossed polarizer method. The magnitude of the retardation that is caused by the flow birefringence is evaluated by the hue change and it is linearly related with shear stress by the stress-optic rule in the low shear rate region. In higher shear rate, the relationship is changed because the micelles change to the other structure, that is, shear induced structure SIS. The stress profile of the steady Couette flow in a concentric cylinder flow cell is a constant and homogeneous generally, even in non-Newtonian fluid. Some of polymer fluids, liquid crystals and the other generate two layers steadily, which is called shear banding. The wormlike micelles solution shows shear-hardening and flow fluctuation at a start-up regime of the step shear flow and then the generation process of the shear bands is not easy to observe. We apply an accelerated shear that the shear rate increases from zero to a target rate with a constant rate. Using this flow, we can observe the process to generate the shear bands without the effect of the shear-hardening. At a certain time after the flow started, a thin layer of the higher retardation is generated near the wall of the inner cylinder which is a driven side. The thickness increases with increasing the shear rate. A new layer appears when the thickness of the first layer achieves about a half of the channel thickness and the flow field is divided by three and more layers. Thickness of these shear bands changes periodically synchronized with the stress fluctuation. This periodic change happens simultaneously in all direction not in partial.

Shear Banding, Flow Birefringence, Wormlike Micelles, Concentric Cylinder Cell

In recent years, refrigerant mixtures have drawn much attention due to better performance in ORC power cycles and better heat transfer characteristics. But, still less is known about the detailed behavior of mixtures in condensers and evaporators. In this work, the flow boiling of the mixture R245fa / Pentane is experimentally examined and visualized. The test section is a transparent circular tube heated by electric current. The behavior of flow in different mass fluxes and heat fluxes has been reported. Visualization provides deeper insight about the mixture flow, so its behavior in condensers and evaporators is easier to predict. Critical Heat Flux (CHF) has been analyzed and compared to previous data.

Flow Boiling, Visualization, R245fa, Pentane, Critical Heat Flux

Birds have the most efficient respiratory system among existing animals. One of the greatest features of the avian respiratory system is air sacs which are stretchy bags. They do not play a direct role in gas exchange. Instead they serve as bellows to bring air into a bird and store extra until expiration, which allows a continuous stream of air through parabronchi where gas exchange takes place. Airsacculitis is one of air sac pathologies. Inflammation causes thickening of air sac walls, and respiration becomes distresses even after light exercise. On the basis of these facts, we hypothesize that the respiratory distress of birds having airsacculitis is a result of failure of the respiratory flow system. The aim of this study is to examine this hypothesis from a fluid mechanical point of view. An avian respiratory system was described with an electrical circuit. The resistance and inductance of each airway were estimated from anatomical data of a domestic fowl. Anterior and posterior air sacs were established at the middle of ventrobronchi and mesobronchi, respectively. Mechanics of air sacs were modeled as a rubber sphere with linear elasticity, and pressures inside the air sacs were incorporated in the electrical circuit as a voltage generator. Given intra-pleural pressure (IPP), we calculated an elastic force of the air sacs, and subsequently the intra-air sac pressure. Then, flow in the avian respiratory system was simulated to calculate a flow volume entering or leaving the air sacs. This process was repeated until cyclically repeatable flow was obtained. The results demonstrated that the total flow volume passing through the parabronchi from the posterior to the anterior side during one respiratory cycle varied depending on the thickness of air sac wall; the total flow volume was the largest at the physiologically normal thickness. In looking at a pressure difference between the anterior and posterior air sacs which determines the flow through the parabronchi, we found that the amplitude of the pressure difference became smaller with an increase in the air sac wall thickness, while a phase difference in a temporal change of the pressure between the anterior and posterior air sacs remained almost constant. Such trends were consistent regardless of respiratory frequency. These results suggested that impairment of breathing of birds with airsacculitis results from a decrease in the pressure difference between the anterior and posterior air sacs that is determinant of driving the air to the parabronchi.

Avian, Lung, Airsacculitis

Regular turbulence-generating grids have been commonly used in fundamental researches because the turbulence structure is close to isotropic and homogeneous. On the other hand, fractal grids have been attracted as new-type of grids. Hurst and Vassilicos (Physics of Fluids, 19, 035103, 2007) conducted experiments with various planar fractal grids and found their unique characteristics that differ from those of regular grid turbulence especially in terms of turbulent length scales. Mazellier and Vassilicos (Physics of Fluids, 22, 075101, 2010) introduced the wake-interaction scale x* (= L02/t0, where L0 and t0 are the length and thickness of the biggest bars, respectively) and found that it mainly represents the flow structure. Recent study by Valente and Vassilicos (Physical Review Letters, 108, 214503, 2012) has clarified that such unique behaviors are observed in the near region downstream of a regular turbulence-generating grid too. However, few researches on scalar transport have been carried out. Our experimental study in a water tunnel (Hoshino, Nagata, Sakai, Suzuki, Ukai, Terashima, Ito, Transactions of the Japan Society of Mechanical Engineers, Series B, 79(799), 304-316, 2013) has revealed that the fractal grid enhances fluid mixing more than a regular grid with the same porosity. However, the details have not been clarified yet and it is not clear if the wake-interaction scale applies to scalar mixing. In this study, therefore, we experimentally investigated the scalar mixing in turbulence generated by regular grids with several sizes in a liquid mixing-layer type flow. The porosity, distance and thickness of the grids, and the flow velocity were varied. Simultaneous measurement for velocities and a concentration were carried out by particle image velocimetry (PIV) and planar laser-induced fluorescence (PLIF), respectively. Preliminary results show that the concentration mixing layer thickness is strongly affected by the thickness of the grid bar and the wake-interaction scales is not the best parameter to characterize the mixing. In the presentation, the better parameter will be introduced and more details will be presented including the relationship between the velocity and scalar fields.

scalar mixing, turbulence

The interaction of a submerged round jet with the free surface was investigated experimentally. Surface wave profile measurements based on laser induced fluorescence (LIF) technique was used to study this flow. Quantitative surface wave profiles were obtained by image processing of the LIF images with appropriate height calibration. It is shown that surface waves are generated by the large-scale structures in the jet flow as they interact with the free surface. These waves propagate at an angle with respect to the flow direction which increases as the Reynolds number is increased. Propagation of the waves in the flow direction is suppressed by the surface current produced by the jet. Dark circular features are observed in shadowgraph images associated with concentrated vorticity normal to the free surface.

Time-resolved LIF, Visualization, Solitary waves, Pattern formation, Fiber optics probe

We have conducted towing tank experiments on air entrainment by a hydrofoil beneath an air-water interface. In order to enhance the performance of air bubble generation, which is an important factor for ship drag reduction of air lubrication technique, three types of hydrofoils are examined: 2D hydrofoils (NACA0012, NACA4412), 3D hydrofoils (delta wing), and hydrofoils with air outlet. While all the three types utilize the negative pressure above the hydrofoil for air entrainment, each type shows a unique behavior of bubble generation. In 2D hydrofoils, the wave form and the flow behavior behind the hydrofoil play an important role for bubble generation, which depend on the hydrofoil shape, angle of attack, and Reynolds and Froude numbers. The leading-edge vortices over the delta wing (3D hydrofoil) enhance the air entrainment and bubble breakup, which result effective bubble injection into the water. The last hydrofoil with the air outlet also generates large volume of air bubbles because of the instability of the air-water interface at the air outlet. In this presentation, we show a series of flow visualization (back lighting method, PIV etc.) around the bubble generating hydrofoils, which provides insights into the optimization of the hydrofoil facility for air bubble generation in the ship drag reduction technique.

Air Entrainment, Bubble Generation, Ship Drag Reduction, Hydrofoil, Multiphase Flow

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Most narratives involve contrast concepts in stories such as “love” versus “death”, which creates dynamism of story to attract readers. We have attempted to detect automatically the keywords that represent the contrast concepts using electronic text processing. The automatic detection algorithm consists of two steps; entropy analysis of word frequency for finding significant words in a story, and negative correlation analysis for finding the pair of words in contrast. Performance tests with Shakespeare’s six plays and Dickens’ six novels have demonstrated the feasibility of the proposed method. Using the present development for the theme-finding process, it is unnecessary to introduce our knowledge about the story into the software prior to the visualization. We have succeeded in fully automatic story visualization without reading the targeted text, which is expected to further advance to computer-aided interpretation/criticism of arts. For instance, our application to Dicknes’ "A Christmas Carol" indicates the most story-contrasting pair of words to be “Marley” and “Spirit,” demonstrating the proper function of the present algorithm. The correlation analysis also implied that Shakespeare’s plays had story contrast stronger than Dickens’ novel as quantitatively proved by the average cross correlation value. Moreover, secondary themes underlying in parallel could be extracted with the present algorithm.

Art and Culture, Story visualization, Computer linguistics, Pattern recognition, Automatic detection

Birds are known to have a more efficient respiratory system than other species. Aerodynamic valving has been hypothesized as one of the mechanisms to rectify the flow without any anatomical valves in the avian respiratory system of a complex geometry. Although this hypothesis has been examined in geometrically simplified geometry models, usage of the simplified geometry cast doubt on the validity of testing the hypothesis. Here we use an anatomically realistic model of the avian lung to examine the hypothesis and show the importance of geometric representation for aerodynamic valving to work effectively. The anatomically realistic representation of the avian lung was obtained. Adult Japanese quails (coturnix japonica) were euthanized by an overdose injection of anesthetic. The lung was scanned with micro-computed tomography (CT) under internal pressurization. The physical representation of airways, namely, the primary bronchi including primary bronchus (PB), the mesobronchi (MB) and its branches of four ventrobronchi (VB) was obtained by image analyses. MB was terminated before the beginning of dorsobronchi, and VBs were cut off at the entrance of air sacs or before branching to parabronchi. Flow was simulated by solving the Navier-Stokes equations and the equation of continuity under the assumption that air was an incompressible Newtonian fluid. Various boundary conditions were examined. First, a time variation of the flow was directly imposed at the inlet of PB, while the same pressure was given to the rest of airways. Second, a time variation of the pressure was given to the outlets, while a constant pressure was assigned at the inlet. This condition simulates more natural respiration. Third, we examined a time variation of the pressure specified for each outlet and presented in other study. Forth, we attempted to couple a 1D electrical circuit model of the avian respiratory system with the 3D geometry. Regardless of the boundary conditions, the results demonstrated that the inflow was accelerated by an abrupt reduction of the cross-sectional area of the primary bronchi at the first ventrobronchial junction, and the flow velocity increased significantly there, significantly increasing convective inertia heading towards MB. A comparison of the flow pattern between different samples proved the occurrence of the aerodynamic valving in all samples, although the effectiveness of aerodynamic valving differed between them. These results clearly demonstrated the occurrence of aerodynamic valving in a real avian lung, and addressed the importance of geometrical configurations to exert aerodynamic valving effectively.

bird, respiratory system, anatomically realistic model, computer simulation

Micro bioanalysis device (MBD), such as micro-TAS and Lab-on-a-chip, is demanded to realize a rapid and high sensitivity diagnosis of biomolecules (for instance, viruses and proteins). An open-well-type MBD, which has micro structures as the reaction field, was developed by many researchers. The reaction field with micro structures was effective to improve the sensitivity and reaction efficiency due to increase of surface-to-volume ratio and reduction of diffusion distance. However, designs of the structures and the surface of the reaction field are still depending on trial and error due to the complicated phenomena which are different in distance between biomolecule and the surface of the reaction field. In this work, we attempt to establish multi-scale modeling of biomolecules diffusion in micro fluid, and to simulate its behavior on the reaction field in open-well-type MBD numerically, and furthermore, to verify of the validity of this model for different phenomena experimentally.
To simulate biomolecule diffusion affected on different forces occurred by fluid flow, electric double layer (EDL) on the surface of the reaction field, Brownian motion and so on, particle tracing method (PTM) was used, which is Newton’s equation of motion intended for the particles as biomolecules. The force terms in this equation consist of fluid drug, electrostatic force by EDL, the force related with Brownian motion and interaction between each particles. The flow rate involved in fluid drug and the voltage in electrostatic force were solved by Navier-Stokes equation and the combination of Poisson-Boltzmann equation and Nernst-Planck equation, respectively. For the simulation of biomolecule diffusion, COMSOL Multiphysics was used, which is the analysis software based on finite element method (FEM). To verify the validity of this model for different phenomena, different droplet behavior in the presence or absence of micro structures and different concentration of nano particles contained in phosphate buffer in pH were observed by high speed camera and particle image velocimetry (PIV), respectively.
By PTM, the biomolecule diffusion between two structures on the reaction field was simulated. The structure height and pitch was 7.5 micro meter and biomolecule diameter was 7.5 nm. The results show that biomolecule diffusion between two structures changed from convective diffusion to molecular diffusion because the diffusion space of biomolecule was formed by the presence of micro structures, and that it is possible to simulate biomolecule diffusion affected on different forces using PTM by coupling the multi-physic forces.

micro bioanalysis device, multiscale modeling, biomolecule diffusion, micro fluidcs, particle tracing method, electric double layer,

Tunable diode laser absorption spectroscopy (TDLAS), as a time-resolved in situ and non-intrusive technique which allows combined measurement of selected gas concentration, temperature and velocity, has shown great potential and advantages in ground tests. Recent advances make it increasingly common to use multiple lasers for simultaneous measurements, this is to say, TDLAS have the capability of temperature tracking measurement of multiple flowfield which suggest excellent potential for flow diagnostics. A specific line pair near 1.4 μm was targeted for low temperature measurement(230K-400K) in the shock tunnel using a scanned- wavelength direct absorption technique. Two DFB diode laser are used to scan over diffierent H2O absorption transtions(7095.85cm-1 and 7168.437cm-1) at a 15kHz repetion rate. For high pressure situation another line pair(7168.43cm-1 and 7185.597cm-1)was selected also in the shock tunnel using a scanned-wavelength technique with wavelength modulation and 2 f/1f detection. The scanned rate is 1kHz and the wavelength is modulated at 250kHz. Fundamental spectroscopic parameters of the selected transitions are determined from Hitran 2012 database which is the latest version, including the temperature-dependent line strength, self-broadening coefficients, and air-broadening coefficients. Two tunalbe diode laser absorption methoed, direct absorption spectroscopy (DAS) and wavelength modulation spectroscopy (WMS), are applied in the shock tunnel flow diagnostics which is capable of simulating flight Mach numbers 6 with a total temperature of 800K to 1600K. In one shock tunnel test with Mach 6, the time-resolved static temperature of nozzle flow is monitored using DAS and that of State 5 shock tube flow is measured by WMS simultaneously. The operation status of the shock tunnel is analysed through combined measurement of temperature and pressure. Tunable diode laser absorption measurement is promising for development into routine diagnostic tools for quasi-one dimensional flow in the shock tunnel. And that is important for reliability judgment of aerodynamic / heat ground tests under hypersonic flow in the shock tunnel.

Temperature measurement, Tunable diode laser absorption spectroscopy, High speed flow monitor, Shock tunnel

The background oriented schlieren (BOS) technique is one of the visualization techniques that enable the quantitative measurement of density information in the flow field with very simple experimental setup. The BOS requires only a background and a digital camera and it can realize the quantitative measurement of density. If there is density change between the background and camera, background image is captured at image sensor with displacement because of the refraction of the light passing through density gradient. The quantitative density measurement can be realized by evaluating the displacement with image analysis.
In this report Colored Grid Background Oriented Schlieren (CGBOS) technique is applied to the measurement of the interaction field of lateral jet and cross flow. The test model is designed based on DLR’s generic model and diameter (D) is 40 mm. Experiments were carried out in supersonic blow-down wind tunnel of JAXA/ISAS with 0.6 m × 0.6 m test section. Free-stream Mach number was set to 2.0. The CGBOS images are recorded by high-speed camera (NAC MEMRECAM HX-3) with 200 fps (flames-per-second). The resolution of the camera is 2560 × 1920 pixels for this condition. In order to increase the depth of field and the accuracy of the CGBOS measurement, telecentric optical system is introduced. This work focuses on capturing unsteady and complex flow field caused by the interaction between cross flow and lateral jet from the object with CGBOS technique. Many experimental and numerical works have been reported by many researchers, however the precise measurement have been made by numerical approach mainly because the phenomena in interaction field is extremely complex. The quantitative experimental data obtained by CGBOS technique and the reconstruction results of the density for the unsteady interaction field between cross flow and lateral jet examined by Computed Tomography (CT) will be reported.

Background oriented schlieren, super sonic flow, computed tomography, lateral jet

We desire to look at time variations of an instantaneous flow field in three-dimensions in order to understand complex flow structures, such as a side jet, because the spatial development of complex fluid flow changes in three-dimensional space. A cross-sectional image of a gaseous flow-field which mixed very small particles, such as smoke, can be visualized by the Mie scattering using a laser sheet. We have tried the flow visualization in three dimensions by laminating a large number of the instantaneously cross-sectional images of the flow field which recorded almost simultaneously using a high-speed digital camera. As a result of considering and comparing the optical systems which can acquire cross-sectional photographs at high speed, an oscillating mirror system was adopted. The scanning laser sheet passes thorough a plano-convex cylinder lens and enters into the flow field so that the sheet is a perpendicular to the camera. Consequently, the optical system mainly consists of a CW laser, a laser line generator lens, an oscillating mirror, and a plano-convex cylinder lens. Moreover, the optical system for decreasing a spread of laser light is introduced, and so the thickness of the laser sheet is approximately 1 mm.
A target of flow visualization is a neighborhood at the nozzle of the jet flow which helium gas is vertically issuing from a round nozzle with 16 mm in a diameter to the ambient air. The jet Reynolds number was set to 800 so that side jets might be generated. In this case, the jet speed at the nozzle exit was 5.9 m/s. A scanning time of the laser sheet was 4.1 msec. A frame rate and resolution of a high-speed digital camera were set to 20,000 fps and 512 by 512 pixels, respectively. By one scan, eighty two cross-sectional images of the jet flow were recorded by the high-speed camera. The given and original images are processed to the edge-enhancement. The processed images of 82 sheets were interpolated in 300 sheets using the bicubic interpolation. A three-dimensional image of the jet flow which involved the side jets was constructed from the 300 images. A part of the constructed image is cut off, and the new cross-section can be displayed. A cross-sectional structure of the ejection point of the side jet is able to be shown for the first time, and the cross-section is a form like a mushroom.

Three-dimensional imaging, Flow visualization, Mie scattering, Laser sheet, Side jet

In order to cool a hypersonic vehicle surface, a supersonic gas film is injected tangentially with the surface, which will cause complex flowfield containing shear layer and boundary layer. The beam will be distorted when propagating through the region, called aero-optics. In this paper, such aero-optical distortions are measured using Background Oriented Schlieren (BOS) technique. All the tests were done in the KD-01 hypersonic shock tunnel, and the synchronization among free flow, gas film and camera is ensured. The hostile signals, such as vibrations of model and BOS system are considered and eliminated through image denoising and deblurring processes. The measurements were perfomed under different supersonic gas film flux and attack of model, and the resultes were compared with the LENS’s holography system results. The comparsion shows that when the gas static pressure is matched with local position, distortions reach minimum. And the BOS technique has been proven to be a valid technology to study aero-optic distortions in hypersonic shock tunnels.

aero-optic distortion, BOS, supersonic tangential gas film, hypersonic

In the fluid dynamics, the investigation on the aerodynamic characteristics is one of important issues. Almost of the former studies are discussed on the flow field and the aerodynamic force of the baseball with the uniform flow speed, namely “the steady state”. The present study focuses to investigate the aerodynamic characteristics of the object with accelerating motion and the goal of this research is to clarify the dependencies with the velocity and the acceleration of the drag coefficient.
We used the baseball and the lacrosse without the seam ball as the experimental models to study the aerodynamic force acting to the accelerating object. Figure 1 shows the schematic picture of the present experiment. The baseball is released from the pitching machine and the motion of the baseball is taken by the CCD and the digital cameras. The trajectory of the baseball is analyzed by the image processing.
The coordinates of the ball in images are abstracted by the image processing. We tested and compared the binarization and the gaussian mask to accurately obtain the center of the ball. The computational results of these methods and the reliable data can be acquired by the binarization rather than the gaussian mask.
However, there are some difficulties on the computation of the velocity and the acceleration because of the treatment of the first and the second differentiation for time. In order to remove the error of the image processing, we conducted the modification of the numerical results by the combination of the least square method and the algebraic treatment.
In the fluid dynamics, the drag characteristics is defined as the uniform flow speeds. However, the fluid drag of the ball in the accelerating motion depends on the instantaneous flow speed. In order to accurately compute the trajectory of the ball, the flow field around the ball is assumed as the ideal fluid and the motion of the sphere without the seam are computed. The comparison of the experimental results and the numerical results with traditional CD (steady model) and the proposed CD function (unsteady model) for the trajectory of the ball of lacrosse and the baseball. The experimental trajectory of the ball could be estimated by the proposed model rather than the traditional model.
We investigated the aerodynamic characteristics of the object with accelerating motion. The binarization is used as the appropriate method to acquire the coordinates of the object as the image processing. In order to estimate the velocity and the acceleration of the ball, we modified the experimental results using the combination of the least square method and the algebraic treatment. The drag coefficient is computed from the image processing and the numerical model with unsteady motion is constructed. The proposed model can accurately estimate the trajectory of the ball.

Baseball, aerodynamics, image processing

In cycling aerodynamics, NACA airfoil and teardrop shape are widely use on bicycles recently. Both of its aerodynamic performances are still being questioned in low Reynolds number range (30 000-50 000) due to early flow separation and vortex generation. The aim of this research is to find a new geometry providing better aerodynamic performances compared with traditional symmetric NACA airfoil and teardrop shape at certain Reynolds number range using 2D Computational Fluid Dynamics. By studying the flow separation point, pressure distribution and flow development on many different foils having the same chord length and thickness, we define all the important geometric parameters influencing the performances. Our final CFD results gave us a new geometry called TE (Truncated Ellipse) following most of the Kammtail principles. The TE shows a much lower drag coefficient along the chord direction of the foil compared with symmetric NACA airfoil and teardrop shape. At low yaw angles (< 15 degrees), the performances are better due to the delayed flow separation which only appears at the back of the foil. At high yaw angles (≥ 15 degrees), the respectable aerodynamic drag coefficient combined with extremely high aerodynamic lift coefficient gives a much lower drag coefficient along the chord direction. This high aerodynamic lift is given by the separation bubble found on the TE at high yaw angle. Our research has implications on the future prospects of bicycle aerodynamic design.

Cycling aerodynamics, 2D-CFD, Aerodynamic coefficients, Flow separation

For the visualization of the flow field such as multi-phase flow, particle image velocimetry (PIV) is commonly used. Particularly in three dimensional PIV techniques, instantaneous and volumetric recording of the dispersed tracer particles is desired. Holo-PIV is the optical method that captures the depth information of the particle locations, the method however has difficulty in recording the successive images. Tomo-PIV is 3D3C velocimetry that employs the multiple cameras in order to recover the depth information of the particles that was lost by the planar sensors, therefore there are difficulties of calibrations due to the multiple cameras.
Light field camera, which is also called a plenoptic camera, was proposed in 1908 by Lippmann. By employing the microlens array, the optical system of the light field imaging system was drastically simplified. The camera employs the two-dimensional microlens array in the vicinity of the sensor. By this structure, the image from the multiple angle of view could be captured by the single camera, instead of the multiple pair of the sensor and lens. From the multiple angular images, the camera could get the depth information from the acquired image on the same principle as the recording by the multiple cameras. Using this depth information, the focal plane could be adjusted as the post processing by the computer, which enables to refocus the particles after the image acquisition, i.e. the volumetric particulate field can be reconstructed for the PIV or spray diagnostics.
This paper firstly reports the concepts of light fields and plenoptic photography which is followed by the demonstrations of the volumetric reconstruction of particulate fields from a light field image. In the experiments, Raytrix R5 camera was used that has 4 Mega pixel sensors. The resultant pixel number of the synthetic images were 1 Mega pixel. From the captured light field image and reconstructed particle images with the different re-focus planes, the effective in-plane and depth spatial resolution was investigated by capturing the light field image of the particulate field. Consecutive particle images enabled us to obtain the instantaneous velocity vector field of the fluid flows. The lens used was Nikkor 85mm f1.8 with an extension tube called PK-13, therefore the camera has 24mm * 24mm view area and about 200mm working distance. The fluid was tap water seeded tracer particles with a diameter of 50μm. The reconstructed volume image was about 20mm in depth direction.

light field camera, multiple angle of view, volumetric particle field, reconstruction, PIV

Some of chromonic dye forms a rod like aggregation and its aqueous solution becomes a chromonic liquid crystal at a certain condition in concentration of the solution and temperature. When the chromonic liquid crystal is applied to a glass substrate by an applicator, the aggregates are oriented to one direction in the thin film and it exhibits an optical anisotropy as birefringence and dichroism. This is used as a retarder or polarizer in the LCD.
The orientation process of the aggregates during application, however, is still unknown in detail. In this study, the relationship between flow behavior on the surface of the meniscus region after the applicator and the orientation of the aggregates is examined with two different shape of applicators, a traditional shape applicator (TA) and an edge type applicator (EA). The TA has about 50 degrees escape angle of its back wall and liquid climbs up on the back wall during application. The EA has about 120 degrees in escape angle. The three-phase boundary line between the liquid, air and solid wall is fixed at the trailing edge and it occurs no climbing up on the back wall.
The velocity profile near the surface of the meniscus is evaluated by PIV technique and the orientation of the aggregates are estimated by the polarimetry method. In the case of EA, the velocity of the surface of the meniscus region increases monotonically from the trailing edge to the end of the meniscus region. It means the meniscus near the free surface flows like a planar elongation. The orientation of the aggregates evaluated by the extinction of the polarized light is higher than the orientation caused by the shear flow in the gap of applicator. In the case of TA, the thickness of the meniscus region increases because the climbing up of the three-phase boundary on the back wall causes. A reverse flow is generated near the back wall and the velocity profile is changed from negative to positive to the end of the meniscus region. In the downstream after the reverse flow, the orientation of the aggregates shows the similar in the case of TA. The comparison between the dried thin file after the application and the orientation during application in the meniscus region shows a good agreement and it is found that the orientation of the aggregates is affected by elongation flow near the surface of the meniscus region.

application, chromonic liquid crystal, orientation

This paper presents the experimental results on similarity velocity profile of vortices inside the cavities, formed between two neighboring girders, under a partially inundated bridge deck. Particle image velocimetry (PIV) and flow visualization technique are both employed to explore the flow field. The approaching flow is subcritical with Froude number varying in the range 0.137–0.381. The velocity characteristics of vortex structure inside the cavities under a partially inundated bridge deck, where water is fully occupied without air-pocket, are mainly investigated. The similarity profile of the azimuthal velocity along an arbitrary line, passing through the vortex core, is uniquely obtained using the measured azimuthal velocities for two different flow types. The selection of the characteristic length and velocity scales used for obtaining the similarity profile is discussed in this study.

inundated bridge decks, partially inundated flow, similarity velocity profile, vortex, cavity flow, particle trajectory technique, particle image velocimetry,

The study of shock wave is of significance in understanding supersonic flow. In this paper, we describe about the three-dimensional (3D) quantitative density measurement technique of unsteady and discharging shock waves. In the experimental research areas the supersonic unsteady flow fields have been commonly observed by qualitative and two-dimensional (2D) visualization methods, such as shadowgraph, color-schlieren, or 2D interferometric photograph images. In addition, unsteady flow fields including shock waves and vortices have not been investigated by experimental method. On the other hand, holography and Computed Tomography (CT) methods have been applied to the measurement of three-dimensional flow fields. Three-dimensional shock-vortex flow field has been investigated by Laser Interferometric Computed Tomography (LICT) density measurement in our laboratory. The flow field including shock waves discharged from two parallel and cylindrical nozzles and the flow fields were successfully reconstructed by Filtered Back Projection (FBP) method or Algebraic Reconstruction Technique (ART). These results can be judged to have the validity and the accuracy by comparison with the CFD model. The LICT measurement is the combination of Mach-Zehnder finite-fringe interferometry and Computed Tomography technique, where N2 pulse laser is used as a light source.
The study of shock-vortex interaction induced by the plurality of holes is of significance in engineering of fluid mixing or combustion. In this study LICT technique is applied to observe more complex flow field than our previous study induced by discharging unsteady shock wave from three cylindrical holes. In addition, high-resolution images can be obtained by using a digital camera. Three-dimensional flow fields are reconstructed by ART from these framed images with different directional angles with shot by shot operation of diaphragmless shock tube of similar delay times of laser pulse. The obtained results and features of high-speed and unsteady flow field will be discussed.

Computed Tomography (CT), Laser Interferometry, Shock-Vortex Flow, 3D Density Distribution, Algebraic Reconstruction Technique (ART)

The time-dependent temperature and metal vapor distributions in a plasma flow during gas metal arc welding (GMAW) are visualized by the spectroscopic approaches that measure the radiative emissions from the metal-containing plasma. GMAW is an indispensable industrial technique which melts and joins separate workpieces using an arc plasma flow and molten metal droplets from the consumable wire.
Although recent studies have reported that the metal vapors significantly change the plasma properties such as electrical conductivity and radiative emission coefficient and strongly affect the heat transfer to the workpieces, the temperature and metal vapor distributions in a plasma flow are still poorly understood because the plasma has too high temperature about 10,000 K to measure by conventional methods.
In this study, we visualize the time-dependent temperature and metal vapor distributions in a plasma flow by the optical emission spectroscopy to investigate the profile of the arc plasma flow in which molten metal drops repeatedly. Abel transformation is adopted to obtain the spatially resolved profiles. Two spectroscopic techniques are simultaneously applied: one is the Fowler-Milne method to the arc plasma consisted of argon shielding gas, and the other is the two-line relative intensity method to an iron-vapor-rich region.
The present measurement reveals that the arc plasma has a bell-like configuration with approximately 10,000 K but a remarkably low temperature zone on and near the arc axis. High concentration of iron vapor is observed in the vicinity of the melting wire. In particular, the region between the wire and the falling droplet exhibits the highest iron concentration. Meanwhile, the region below the droplet shows a lower iron concentration.

Optical emission spectroscopy, Plasma temperature, Metal vapor concentration, Gas metal arc welding

Background:
Recently adaptability for environmental problems is required for road vehicles, and consequently reduction of the aerodynamic drag attracts attention, because drag reduction has great effects on the fuel efficiency and the maximum speed. Further in the case of high-performance road vehicles increase of downforce is essential. If flow fields can be visualized conveniently, improvements of aerodynamic characteristics can be performed efficiently. Here the five-hole Pitot tube is noticed, because the measurement technique is easy to be combined with CAFV (Computer Aided Flow Visualization).

Objectives:
The objective of this study is to establish measurement technique by a five-hole Pitot tube, to apply it to visualization of flow-fields about car models in wind-tunnel experiments, and to show its effectiveness for improvements of aerodynamic characteristics.

Methods:
In five-hole Pitot tubes, the pressure signals at the five holes on the sphere part are transmitted through vinyl tubes to semiconductor pressure sensors simultaneously. From the five pressure values the velocity vector can be calculated. It is necessary to perform the pressure measurement in advance and generate the calibration map. Two types of car models are adopted for flow measurement and visualization.

Results and Conclusions:
The first application is for car models whose configuration is systematically changed with two parameters of side and rear angles. In the cases of side angles 0° and 15°, the drag was increased abruptly at rear angles 25° and 30°, respectively, while in the case of side angle 30° this well-known tendency was not detected. By flow visualization it was confirmed that as the side window becomes slanted, generation of the large-scale longitudinal vortex is suppressed. The second application is for car models with or without a roof vane and a rear wing. By flow visualization it was confirmed that with existence of the roof vane the airflow impinges at the rear wing with higher speed, and the downforce can be increased.
Thus, the flow structure was clearly visualized with this technique and the course for improvements of aerodynamic characteristics has been easily attained.

five-hole Ptot tube, Velocity vectors, Aerodynamic characteristics

Unsteady flow phenomena in the transonic region are important issues for aerospace engineering. Especially, shock wave oscillation on a wing and a rocket fairing are one of the most serious problems. The number of the experiments in which the flow field includes shock wave oscillation is increasing in the JAXA 2m by 2m transonic wind tunnel. In those wind tunnel experiments, optical measurements, particle image velocimetry (PIV) and pressure sensitive paint (PSP) are often applied to measure instantaneous velocity and pressure fields.
The purpose of this study is to produce flow fields including periodic shock wave oscillation with a small fluidic actuator because those flow fields are useful for the preliminarily experiment for several visualization techniques. A Hartmann tube is one of the candidates because it is small and produces those flow fields easily. In this study, the velocity fields produced by the Hartmann tube were measured with time-resolved particle image velocimetry in order to investigate the operating condition which is appropriate for the preliminary experiment of several flow visualization techniques and of those analysis and correction methods. The influence of the cavity length and the stagnation pressure on the velocity fluctuation and distribution are investigated.
The shock wave oscillation and the periodical velocity fluctuation are produced by the jet and cavity interaction when the cavity entrance is in the compression region of the under-expanded jet. The velocity fluctuation is large in the region close to the cavity entrance. In the region, the stagnation point and reverse flow are observed. The velocity fluctuation is small in the region close to the nozzle exit. Hence, the region close to the cavity entrance should be chosen for the preliminary experiment. The peak frequency of the velocity fluctuation can be changed by the cavity length. The frequency can be accurately estimated from the quarter wave frequency when the tube length is long. The influence of the cavity length on the amplitude of the velocity fluctuation was small at the stagnation pressure of 2.0kg/cm2G. The amplitude of the velocity fluctuation can be increased to raise the stagnation pressure when the cavity entrance is located in the compression region. At the cavity length of 20mm, the maximum amplitude of the velocity fluctuation is higher than 200m/s. The influence of the stagnation pressure on the peak frequency is small.

PIV, Shock wave, Hartmann tube

This study proposes high speed phase-shifting interferometer for transient heat transfer and fluid dynamic phenomena. This phase-shifting interferometer is marked by phase-shifting technique and a novel prism. Phase-shifting technique is an image processing technique and this technique offers high phase and spatial resolution by converting conventional interferogram to phase-shifted data.
Since this interferometer introduces three step phase-shifting technique, three interferograms are needed. A novel prism has been designed to obtain the interferograms. This prism produces four images including the interferograms in the same direction and the images can be recorded by one camera. Hence, this interferometer can create quantitative visualization of transient high speed phenomena by using high speed camera.
Thermal conduction in liquid was visualized quantitatively as an example of experiments for high speed phenomena in this work. In the experiments, a tungsten wire with a diameter of 5 μm was set in a test cell filled with liquid and the wire was heated electrically within 50 ms.
A transient temperature field around the wire was investigated when the wire heated. The observation area size is approximately 200 μm×800 μm and the spatial resolution is 0.9 μm. The time resolution was changed from 500 fps to 2000 fps by using high speed camera. For measurement of temperature fields, Abel transform was adopted because the temperature field around the wire can be assumed to be axisymmetric. Thus, the radial temperature distribution was measured from phase-shifted data with high resolutions.

Interferometry, Phase-shifting technique, Temperature measurement, High speed phenomena

In the present study, a small scale pool test rig with a single heater rod simulates the PAFS (Passive Auxiliary Feedwater System) prototype and the volumetric scaling ratio of the test rig is 1/910. Two-dimensional temperature distribution and velocity vector fields during the decrease of water level were experimentally investigated in a pool which has a horizontal heater rod. The 2D PIV and LIF measurement technique is adopted to get velocity vector field and temperature distribution of a natural circulation flow and thermal stratification. Experimental results show a large natural circulation flow above a heater rod and thermal stratification below a heater rod. Thermal stratification and no flow region start to break up when pool temperature is saturation temperature. The CFD-grade experimental results will contribute to provide the benchmark data for validating the calculation of thermal hydraulic phenomena inside a pool with a heat source.

Natural Circulation, Thermal Stratification, Flow Visualization, Pool Boiling

The ocean flow field is mixture of multi-scale vortices and streams that have ambiguous boundary lines in nature. Meanwhile, these vortices and streams change their form and velocity at every moment. The ambiguity of boundaries and unremitting transition make us difficult to recognize the ocean flow structure. In order to support recognition, we introduce the new visualization method that segments the ocean flow field to each vortex and stream, and visualizes the scales of them. The boundary of vortices is defined as the closed line that indicates tangency area of vortex-core region (which mass does not mix with outer mass) and outer flow region. The boundaries of streams are defined as valley lines of the flow speed distribution. We suggest different segmentation method for vortices and for streams.
Vortices Extraction: Search the critical points (the saddle/vortex center points) and calculate FSLE (the finite-size Lyapunov exponents) for entire field. Then, generate stream lines from points that are located at vicinity of the saddle point and have high FSLE value. The vortex-core region is not intruded by any of those stream lines because the mass does not mix with stream field mass. The closed regions segmented with the stream lines that include the vortex center point can be extracted as vortices.
Streams Extraction: Search the velocity maximum points that compose stream axis for entire field. Remove the maximum points that has high velocity gradient to adjacent maximum points to separate the stream axis to axes of each stream. This separation is in accordance with human intuitive recognition that recognize group of similar velocity region as a stream. Surrounding areas are grouped to these stream axes. The grouped regions are extracted as streams.
The boundary lines and scales mapped to colors are visualized. Our visualization supports human recognition of this perplexing ocean flow field from the following aspects. (1) Clearly defined boundaries detected with our method reduce users load to recognize flow forms. (2) Detected boundaries make even subtle streams or vortices stand out in bold relief. (3) Flow transition like merge or diverge is captured as obvious change of view (for example: color) since the scale of corresponding region drastically changes when it occurs.
We expect that our visualization method will provide intuitive view of the ocean flow filed for general users, and provides other alternatives for scientific analysis of currents by utilizing boundaries.

Vortex, Stream, Boundary, Extraction method

Summary
The present paper describes results of numerical analysis on supersonic flow field, at Mach 2.0, around a Disk Gap Band type parachute as deceleration device for planetary probes. In this report, the analysis was focused on the flow field around supersonic parachute. A commercially available hydro-code, AUTODYN (ANSYS) was employed for the analysis. The result clearly shows the flow field including shock waves and confirmed pressure change in the canopy. We will extend the procedure described in the present report to simulate the flow field around the DGB-type parachute consisting of flexible material in near future.
Purpose
The purpose was stable flight of the supersonic parachutes in entry to mars. Consequently, the analysis was resolution which was inducted to shock wave around the supersonic parachute. Therefore, AUTODYN was used for analyzing the numerical analysis on flow fields around supersonic parachutes.
Model description
The supersonic parachute was a Disk Gap Band (DGB) type. This type was using to decelerate for a mars space probe in entry to mars, e.g. VIKING project. We analyzed two models, that supersonic parachute model were assumed rigid body. The first was entire parachute model, including capsule, suspensions, and canopy. The second was only canopy model, focus on the canopy in detail.
Numerical analysis
A commercially available hydro-code, AUTODYN (ANSYS) was employed for the analysis, in order to calculate the flow field around the supersonic parachutes. All the analysis conditions were same, flow speed was Mach 2.0 and the flowing gas was ideal air. We calculated two models which are entire parachute model and only canopy model at same conditions. In the case of entire model, the result clearly shows the flow field including shock waves, two bow shocks were checked that had made in front of the capsule and canopy. The inside air of the canopy was going out from gap section. In the case of only canopy model, confirmed pressure change in the canopy.
Future
As the next stage, we are doing quantitative analysis. Then, we will compare and explain between the experiment result and calculation result. Furthermore, doing coupled analysis of the flow and the motion, when the parachute model is flexible structure.

Numerical analysis, Supersonic parachute, Supersonic flow

A novel technique of phase-shifting digital holography has been implemented in the 3D particle tracking velocimetry and thereby the quality of reconstructed particle images and the accuracy of their depth detection have been improved. The new phase-shifting technique is based on a quasi instantaneous holographic recording system using two independently frequency modulated optical paths and a high-speed CMOS camera. Phase-shifting holographic images are automatically recorded at full resolution of the CMOS camera by the principle of heterodyne interferometry. More specifically, the modulation frequency of the two optical paths, one is for the object light and the other is for the reference light, is differentiated by a quarter of the frame rate of the CMOS high-speed camera. In consequence, on the CMOS sensor are recorded a time series of phase-shifting images of which the phase lag between every two consecutive frames is pi/4. This technique is more advantageous than the conventional phase-shifting technique using mechanical phase shifter devices (e.g. piezoelectric actuator) in the sense that the phase shift can be more accurately controlled and far more rapidly (quasi instantaneously) repeatable. Test results of this technique demonstrate the strength of the new methodology from the viewpoint of the reconstructed image quality and the particle depth accuracy.

Particle tracking velocimetry, Phase-shifing, Digital holography, Optical modulation, Heterodyne interferometry

The background oriented schlieren (BOS) technique is one of the visualization techniques that enable the quantitative measurement of density information in the flow field with very simple experimental setup. The BOS requires only a background and a digital camera and it can realize the quantitative measurement of density. If there is density change between the background and camera, background image is captured at image sensor with displacement because of the refraction of the light passing through density gradient. The quantitative density measurement can be realized by evaluating the displacement with image analysis.
In this report Colored Grid Background Oriented Schlieren (CGBOS) technique is applied to the measurement of the natural convection. Twelve digital cameras are employed to realize the simultaneous multi angle observation to the unsteady phenomena. The normal digital cameras (Canon EOS Kiss Digital X3) are used to construct the multi-angle CGBOS measurement system with low-cost. To realize the three-dimensional (3-D) measurement of unsteady density field with CT (Computed Tomography) technique, simultaneous measurement system is necessary. The prospect of the measurement system will be discussed and the measurement results will be reported.

Background oriented schlieren, natural convection, computed tomography, simultaneous measurement

This study proposes a measurement technique of temperature and velocity distribution of airflow using a visualization technique using fluorescent mists, Two-color laser-induced fluorescence (LIF) method and color PIV. The two-color LIF method is used for measuring the temperature distribution of an airflow by spraying a mist of a fluorescent dye. The mist is generated by using propylene glycol, the vapor pressure of which is much lower than that of water, as the solvent of the fluorescent dyes. A supersonic moisture chamber is used as the atomizer for seeding the tracer particles to be visualized. The velocity distribution is also measured using color PIV technique simultaneously. A color digital single-lens reflex (SLR) camera and two illumination colors are used to simultaneously obtain two pairs of time delays. Visualization images are obtained by a color digital SLR camera with color (Red and Blue) pixel image grids. The proposed technique is applied to the measurement of the temperature and velocity distribution in a thermal vertical buoyant plume.

Visualization, LIF, Color PIV, Simultaneous measurement

In order to develop the optical distortion of optical window which is under the condition of heating, this paper shows a series of experimental studies about the thermo-optic effect of the optical window by two methods of traditional Oriented Schlieren and Background of Oriented Schlieren(BOS).The traditional Oriented Schlieren technique qualitatively shows the basic discipline of the refractive index of the optical window varies with temperature, the BOS technique uses a high-speed camera to shoot background point image in tow cases of the optical window are unheated and heated, and then makes the cross-correlation analysis of the two images by image processing software, then obtains the offsets of the background particles, and then it is obtained light deflection angle because of the temperature field. We can obtain the change of the refractive index and the distribution of temperature. Two methods used in this paper similarly reveal the light may occur deflection when the light through the optical window existing temperature gradient, and the discipline of the refractive index of optical window varies with temperature studied by both method is consistent.

Oriented Schlieren; Background Oriented Schlieren (BOS) Technique; Optical window; Thermo-optic Effect

In the aerodynamics, the investigation on the flutter is one of important issue to develop the airplane flying with high speed. There are many researches on the flutter phenomena in the past. However, number of systematic experimental studies is only a few. The purpose of the present research is to classify the relationship between the flutter mode and the flow pattern to the velocity and the material properties and to propose the non-dimensional parameters of the fluid force to the elastic forces for the estimation of the flutter phenomena.
We made the experimental device to simulate the sheet flutter and conducted the experiments using the low-speed wind tunnel facilities. Area of the cross section of wind tunnel has 0.3m x 0.3m. Some kinds of sheet for the present experiment are selected and we use the silicone rubber, vinyl, urethane, PVC and EPT. Flow speeds are varied from 0 to 40 m/s. Various sizes of sheet are tested to investigate the flutter characteristics and the flow pattern. We measure the displacement of the sheet flutter using the later displacement sensor. 3D-motion analysis system is used to analyze the motion of the sheet flutter and the flutter mode is classified with the flow speed. PIV system is used to investigate the flow field of the sheet flutter.
The start point of sheet flutter with increasing the flow speed and the end point of that with decreasing the flow speed are different and the motion of the sheet is varied within the flow speed of the flutter boundary. From the results of the laser displacement sensor, we compute the frequency of the oscillating sheet. Frequency of sheet flutter is gradually increasing to the flow speed and our results are well agreements with the past results by other researchers. The results of the 3D-motion analysis are validated by comparison with those of the laser displacement sensor and the discrepancies of each result are within 0.5 percentages. The above results showed that our measurement is a reliable data to discuss the motion of sheet flutter and the flutter mode.
We combine the 3D-motion analysis with the PIV system and to investigate the classification of the flutter mode with the flow pattern to the velocity and the material properties. As the results, we reveal that the formation of vortex over the surface of the sheet is one of the key roles to the criterion of flutter mode. We continue to analyze the experimental results and we will propose the non-dimensional parameters of the fluid force to the elastic forces on the ISFV16 conference.

3-D motion analysis, aerodynamics, PIV, sheet flutter.

Flame front identification is an important part of combustion research in order to identify the flame regime. An approach to visualize the flame front in a plane without a laser application is presented; this technique might be an alternative to Particle Image Velocimetry (PIV) or planar Laser Induced Fluorescence (OH-PLIF) measurements.
The light emission of a methane-air flame is recorded with an intensified high-speed camera and a Cassegrain telescope. This specially designed Cassegrain telescope (composed of a convex and a concave mirror; 300 mm working distance; 20 mm image diagonal) has a very high light collection rate in the focused plane and therefore reduces the line-of-sight integration known from standard lenses. Additionally, the mirror optics offers a very low depth-of-field combined with a good light intensity. Hence, the flame structure in the focus plane can be evaluated with good accuracy. An edge filter is used for the identification of the flame front in the recordings. The strong gradients of the image intensity indicate the location of the flame front; in addition to the strength of the intensity gradient, the qualification of an edge as flame front is characterized by a strong curvature in its vicinity.
PIV recordings taken simultaneously to the Cassegrain recordings (no significant changes in the flame shape during the 10 µs time delay between the second PIV laser shot and the Cassegrain recording) validate the proposed method. The volume expansion over the flame front strongly reduces the particle density in the Mie scattering images and clearly indicates the location of the flame front. The results show good accordance between the flame front location identified with the Cassegrain optics and the PIV system.
In conclusion, the proposed method reliably identifies the flame front, if conservative settings for the edge detection are applied: Not all valid flame fronts are detected, but all detected flame fronts are valid.

Cassegrain Telescope PIV Flame Front Identification

Instantaneous velocity profiles of bubbles and liquid in gas-liquid bubbly two-phase flow are visualized using multiwave ultrasound (2MHz and 8MHz frequencies) and signal processing techniques. The ultrasounds are generated and received using spike pulser/receivers (P/Rs) and multiwave ultrasonic transducer (multiwave TDX). The multiwave TDX is able to emit and receive ultrasounds of 2MHz and 8MHz frequencies at the same time and position. 2MHz frequency is used for measurement of velocity profile of bubbles. 8MHz frequency is used for that of liquid. As a result, velocity profiles of bubbles and liquid can be obtained simultaneously along one measurement line. Instead of using tone burst P/Rs, more commonly used and low-cost spike P/Rs of ultrasonic inspection industry are used to drive the multiwave TDX for the generation of ultrasound. However, spike signal has a broadband spectrum. In order to obtain ultrasound of the required center frequencies, it is found that damping effect has a decisive role. At high damping, analysis shows that power spectral density peaks at 2MHz and 8MHs. Therefore, velocity profiles can be obtained. Practical measurements and analyses have been carried out for bubbly flow in a vertical pipe. Results have been confirmed.

instantaneous velocity profile, multiwave ultrasound, damping effect, two-phase flow, bubbly flow

Much effort has been undertaken for the estimation of propulsive force of insects. A quasi-steady-state approach has led to errors in predicting the fluid forces acting on an insect wing, suggesting that flight is impossible. However, because biological flight does occur, the effect of unsteady fluid forces must be important to flight. The propulsive force of these animals relates to unsteady fluid forces accompanied with the movement of vortices. The unsteady fluid forces must also be considered when estimating the propulsive force of swimming doing the front crawl and the flat scull technique in synchronized swimming. The propulsive force of swimmers in the front crawl is mainly generated by hand motion, and the actual motion of a hand is obviously unsteady.
The purpose of this study is to elucidate the relationship between three-dimensional vortex structure and unsteady fluid forces. In the present study, the vortex structure and its behavior of a discoid airfoil simulating a swimmer’s hand are investigated during pitching oscillations. In general, there are many parameters to be considered for unsteady phenomena, and therefore it is difficult to elucidate unsteady mechanisms. In this experiment, a wind tunnel test is used to evaluate the vortical flow field, because complex parameters affecting unsteady phenomena can easily be changed in a wind tunnel test. The pitching motion was performed by using a five-phase stepping motor. The angle of attack α of the model varied with the function α=αc+Asin(2πft), where A is the amplitude, αc is the angle of the pitching center and f is the oscillation frequency. The non-dimensional time t’ is defined as t’=t/T, where T is total time of one oscillation cycle. The discoid airfoil has a chord c of 150 mm, the maximum thickness was 37.5mm. The vortical flow fields were measured in the wake of the discoid airfoil using a stereoscopic PIV technique. The stereoscopic PIV system consists of a laser, two CCD cameras and a pulse generator. The flow fields were measured using a timing cycle generated by the trigger of the pulse generator to synchronize the image capture with the airfoil motion. The image of three-dimensional vortex structure is depicted by plotting iso-vorticity surface calculated from the reconstructed velocity data. The vortex grows near the upper edge of the airfoil during the downstroke(t’=0～0.4), and the vortex shedding happens from the upper edge of the airfoil at t’＝0.4.

Unsteady Flow, Vortex, Vortex Ring, Unsteady fluid force, Pitching Oscillation

The dilute phase pneumatic conveying is a most popular transport technique of materials and is extensively used in various industrial processes for more than a century, but it often causes higher power consumption, pipe erosion and particle degradation. To overcome these problems, pneumatic conveying often operates at low air velocity. However, the conveyed particles are easily deposit on the bottom of the pipeline due to the force of gravity. These sediments may result in large pressure loss, high fluctuation of pressure, and blockage of the transport line. Therefore it is important to keep the pressure drop and conveying velocity as low as possible without the appearance of material sediments in the design of pneumatic conveying system. So far, some investigators developed some energy-saving techniques, such as swirling flow pneumatic conveying which studies could reduce the conveying velocities and the pressure drops. However, an important question to be asked is how particles motion in the swirling flow at low air velocity. This is important for designing the saving-energy pneumatic conveying and motivates the present investigation. The purpose of this study focuses on the measurement particle velocity near the minimum pressure drop by using high-speed PIV. The test pipeline consisted of a 5m-long horizontal straight acrylic tube, having an inside diameter of 80 mm. The polyethylene particles with diameter of 2.3 mm were used as conveying materials. The superficial air velocity was varied from 10 to 14 m/s, and the solid mass flow rate was fixed at 0.45 kg/s. A high-speed camera with a resolution of 1024X1024 pixels is adopted to capture the successive digital particle images at a frame rate of 1000 fps (frame per second) and the shutter speed of each frame is set at 0.1 ms. A laser light-sheet of 2 mm thickness is used to illuminate the objective particulate flow. It is found that the particle velocity of swirling flow is larger than that of the conventional pneumatic conveying, which results in the reduction of conveying velocity.

Gas-solid two phase flow, High-speed PIV, Particle velocity, Pneumatic conveying, Pressure drop, Swirling flow

Heat flux measurement in a hypersonic wind tunnel is an indispensable requirement for designing a next generation reentry vehicle.
Typically, the method of measurement with a thermocouple is dependent on the model shape and the number of sensors. Thus, we can only get discrete data. In contrast, we can get a full-field image of the temperature distribution on the model surface by using Temperature-Sensitive paint (TSP).
Currently, the simulation of a spacecraft re-entry is conducted with a shock tube and a wind tunnel. Test times of some of the equipment are extremely short, therefore we cannot use standard TSP which does not have enough response time. Thus, we need to develop a new TSP to get the temperature and heat flux data by using a wind tunnel with a short test time. Furthermore, a high sampling rate is required to be utilized alongside the high speed phenomenon. Because of this, we need the exposure time to be very short however this will result in the recorded images becoming too dark. If the film thickness of the TSP layer is thicker, the amount of luminescence increases，but it would be appear that there is an effect on the response time of the TSP．So the TSP with a large luminescent intensity and adequate response time is required. Then, we developed the new TSP and investigated the temperature sensitivity, the luminescent intensity and the response time. We applied the new TSP to the high-enthalpy wind tunnels. In this paper, we repot the preliminaly results.

TSP, Hypersonic flow, Aerodynamic Heating

In order to understand the details of the flow field in the micro- and nano- fluidic devices, it is necessary to measure the three-dimensional velocity field under a microscopy. Thus, the development of a new measuring technique for the three-dimensional velocity by a single camera is strongly needed. One solution is the use of holography, but it has been known that the resolution in the depth direction is very poor for the commonly used in-line holography. Presently, the Doppler-phase-shifting holography has been used for the three-dimensional measurement of an object. This method extracts the signal of a fixed frequency caused by the Doppler howling between the object light and the reference light, either or both of which travels at a constant speed. Applying the shifting to the holography, the three-dimensional shape of an object can be measured very precisely. Here, the frequency of the Doppler howling is determined by the velocity difference between the object light and the reference light. This implies that the velocity of an object can be measured by the Doppler frequency. In this study, a concave mirror was traversed at a constant speed and its holography has been observed by a high-speed camera. By extracting only the first order refraction signal at the Doppler frequency, the 0th order object light can be removed from the hologram and thus a precise measurement of the surface profile has been achieved. At the same time, the lateral velocity of the mirror can be measured by the Doppler frequency. Furthermore, a 5 yen coin has been traversed by different velocities at different angles and its shapes and the three-dimensional velocities have been measured. The transverse velocities are measured by the PIV algorithm and at the same time the longitudinal velocity is measured by the Doppler frequency. The results reveal that the precise measurement of the three-dimensional velocity by a single camera is possible by the use of the Doppler-phase-shifting holography. This method can be applied to the particles motions in the micro- or nano- devices, and thus the three-dimensional velocities will be measured under a microscopy.

digital holography, PIV, three-dimensional measurement, Doppler-phase-shifting

The application of renewable energy becomes current trends. In Taiwan, solar energy and wind energy are more popular. The application of solar energy frequently used in installation of solar water heater. However, the typhoon is one of the nature disasters in Taiwan. Solar water heater is usually installed on the top of a building which is without any cover. The wind directions changes due to some factor of seasons or surroundings of the installed location. That may destroy solar water heaters. In this study, a single plate of heat collector which is 60% of the original size is used as the geometric model. The pressure-based finited volume scheme with Realizable k-ε turbulent model is applied for simulation. Owing to the simulated data close to the experiment data, the turbulent intensity and length scale are 11.7% and 0.12m individually. The studies are consist of a solar collector with inflow angle （θ=15°、22.5°、30°、37.5°）and with different guide plate atθ=22.5°. The result shows that low pressure area on upper surface is expanding when inflow angle increased to 30° ,and it’s reducing when inflow angleθ=37.5°. The high pressure area on the lower surface is increased near the left side. Total lift force is increased by the aspect ratio of the cross section in front view. Total drag force is reduced by the changes of the area on the vertical section of the inflow. With a guide plate, the inflow impacts the plates directly, and can reduce the differential pressure between the upper and lower surface on a solar collector. When length of guiding plate increases, shielding effect is more augmented. When the guide plate shorted, the lift force is also increased.

Solar collector, CFD, Inflow, Wind incidence angle, Lift

It is common for a re-entry vehicle to have a blunt bottom surface to decelerate its speed down to low subsonic one with an aid of air. However, it is known that such flat-nosed capsule has a tendency to exhibit severe pitching and yawing vibrations especially in transonic flight speed. This nature is called dynamic instability. In order to investigate the dynamic instability of a re-entry vehicle in wind tunnel, the dynamic test apparatus was fabricated, which allows a model to rotate around the pitch, yaw and roll axes. With this apparatus a vehicle model can rotate freely in a freestream immediately after a locking device is deactivated. With the vehicle model with its position of the center of gravity off the symmetry axis, the degree of the dynamic stability may differ in the pitch and yaw plan, because the trim angles differ. The dynamic tests with such model were carried out in the flows of Mach 0.5 and 1.1. It is found that the model is dynamically stable both in pith and yaw even if the trim angles differ. However, it exhibited a rapid rolling motion at Mach 0.5. In order to investigate the flow around the rotating model, the flow visualizations using the schlieren technique and tufts were applied in the wind tunnel.

Schlieren, Re-entry, Dynamic instability

Bubble clusters which are naturally formed during their advection in a horizontal channel flows significantly modify the local and global skin frictional drag. The phenomenon cannot be mathematically modeled by the linear sum of bubble-liquid interaction, but it should be assessed with multi-scale modeling in densely dispersed multiphase flow. We have developed a novel image processing scheme to detect gas-liquid interfaces of all the individual bubbles so that bubble clustering process from its initiation until the collapse is quantitatively visualized. Backlight images of complicatedly migrating bubbles interacting with wall turbulence were recorded by a high-speed digital video camera at 1000 fps in frame rate, and 1/20,000 in shutter speed, coupled with particle tracking velocimetry that resolves two-dimensional relative velocity vectors among bubbles. A series of original geometrical definitions have been proposed to characterize the bubble cluster behavior, such as statistical uniformity of spatial bubble arrangement, Lagrangian bubble-bubble interactive velocity field, Eulerian spectral responses of void fraction, and also bubbles’ radial distribution function. From the data analysis, we have found that bubble clustering remains potentially in any flow conditions including the case of large bubble-size deviation, and stands out strongly as superficial void waves where turbulence of liquid phase and bubble cluster are mechanically coupled in the same length scales.

Bubbly flow, Bubble cluster, Void wave, Image processing, Horizontal channel flow

Microscopic flows are usually very simple in nature as the Reynolds number is low and the flow laminar. Moreover, the geometries are not complex so that even the boundary conditions do not lead to complex flow patterns. However, in microfluidics the flow complexity often results from the interaction of particles, transported by the flow, or due to external flow manipulation procedures such as acoustic, electric or thermal fields. These flow control techniques are very popular in order to manipulate the flow in a desired way to sort or mix particles or to mix substances over a very short spatial domain. The experimental visualization of complex unsteady 3D flows in microfluidics is very challenging with established techniques because of the limited optical access or intrinsic calibration problems. Therefore, a new technique has been developed over the last years, to measure the motion of tracer particles by using astigmatic imaging optics in combination with novel particle image detection schemes. Recently, the technique was extended to simultaneously measure the 3D velocity and temperature fields and can be used to also calculate the volumetric pressure field using the flow velocities. On the other hand, the technique could be extended for macroscopic applications in jet engines and turbines. The principle of the measurement technique and its application for microscopic and macroscopic flows will be outlined in the presentation.

Microfluidics, flow control, PIV, PTV

A capillary-driven passive heat transfer device made of thermally refractory metals (molybdenum or niobium) can be used as a formidable solution for successful thermal management on hypersonic flight vehicles exposed to extremely high-temperature environments. Two-phase cooling devices, such as a heat pipe, using a liquid-metal coolant (lithium or sodium) will be able to passively provide extremely high thermal cooling fluxes. Imaging of the liquid-metal coolant inside will provide valuable information in characterizing the detailed heat and mass transport phenomena of high-temperature liquid metal heat pipe devices. Neutron imaging possesses an inherent advantage from the fact that neutrons penetrate the heat pipe metal walls (Mo or Nb) with very little attenuation, but are significantly attenuated by the liquid metal (Li or Na) contained inside.

Using both the BT-2 beam line at the National Institute of Standards and Technology (NIST) in Gaithersburg, Maryland, and the CG-1D beam line at the High Flux Isotope Reactor (HFIR) of Oak Ridge National Laboratory (ORNL) in Oak Ridge, Tennessee, experimental visualization efforts have been conducted on various heat pipes operating at high temperatures of up to 1100C. For a cylindrical heat pipe model with a square bore inside, the time-dependent capillary actions were recorded to examine the meniscus shapes and the bulk meniscus height variations. For a leading edge type heat pipe prototype with meshed wicking structure laid inside, simultaneous neutron imaging and heat transfer experiment was conducted to investigate any thermo-physical correlation of the movement of the liquid metal coolant with the heat pipe cooling performances. Furthermore, a three-dimensional tomographic image was also reconstructed from the total of 128 projection images taken 1.4o apart with 180s of exposure time for each image.

Neutron imaging, high-temperature heat pipe, liquid meatal coolants, sodium and lithium, tomography

Molten core concrete interaction (MCCI) has been analyzed by using moving particle semi-implicit (MPS) method. Proper model is used to simulate the probable stratification between metal and metallic oxide. Besides that, gas generating due to the chemical reaction between corium and concrete also been considered. Heat transfer is calculated by solve the energy equation without any empirical formula. Particles’ phase is changed based on the enthalpy. Natural convection in the melting pool is considered using Boussinesq’s approximation. Radiation heat transfer between the corium and water pool is also been calculated. CCI experiment is simulated by using this code, and the result is fixed very well with the experiment data. Stable crust is formed in the top of melting pool, which is tremendously decrease the heat transfer from corium to water pool.

MCCI, MPS, phase change, ablation

In the event of a severe accident inside a nuclear reactor, the core may melt and relocate to the lower head of the Reactor Pressure Vessel (RPV). The core melt will heat the lower head and may cause the failure of the RPV. Severe Accident Management Guidelines (SAMG) exist to prevent accidents from occurring. A particular safety method that may prevent the RPV failure is In-Vessel Retention (IVR). During the application of IVR, the reactor cavity is flooded with water. By doing so, the melted core can be retained inside the RPV by cooling the outer wall of the vessel. The IVR method is mainly applicable for Pressurized Water Reactors (PWR). For example, the Westinghouse AP-1000 is well known for implementing IVR. Can the IVR method be applied in Boiling Water Reactors (BWR)? It may be feasible since the concept is similar (cavity flooding). Consider the process of In-Vessel Retention: the cavity area is flooded with water, and the heat from the vessel wall is removed as the water fills the gap between the insulation and the RPV. One main difference between PWRs and BWRs is the Control Rod Drive (CRD) penetrations in the lower head of the BWR. These penetrations may affect the heat transfer during IVR, which is the focus of this study. Cavity flooding has been considered for new BWR containment designs. The reason for the cavity flooding is mainly to reduce containment pressure during severe accidents. Currently IVR is not being considered in the new designs due to implementation of the core catcher. The safety of the system can be enhanced if BWRs were to include the IVR method, in addition to the core catcher, as a severe accident management procedure.

IVR, Ex-vessel Cooling, BWR Penetrations, Heat Transfer

To understand characteristics of Pressure-Sensitive Paint (PSP) with ceramic particles, the effects of particle size, particle content, layer thickness and the application method of dye on PSP were studied. The sizes of particle used in this study were 15 nm, 80 nm, 500 nm, and the particle content of PSP was changed from 0 to 90% to investigate static and dynamic characteristics of each sample. Static pressure and temperature sensitivities were evaluated by using a calibration chamber and CCD camera. Pressure was controlled from 80 to 120 kPa, and temperature controlled from 5 to 25 °C. For investigation dynamic characteristics of PSP, a calibration device consisting of a solenoid valve, high-voltage power source and a test cell was developed to create a step change in pressure. With this device, step response of PSP luminescence was evaluated. In this study, two types of analytical procedure were introduced to evaluate the time response of PSP. The PMT data in a step response experiment was transformed to pressure using Stern-Volmer relation, and the rise time was calculated. The other procedure was a least-square fitting of the measured data to a multi-exponential function to determine the factors influencing PSP response.
The pressure and temperature sensitivities for “mixed” and “adsorbed” PSP tend to become worse as the particle content increases. The thickness of PSP layer has no significant effect on both types of PSPs. The sensitivities of both types of PSPs are similar from a quantitative view point. It is noted that static characteristics of PSP come closer to those of the conventional PC-PSP, as the particle content increases. On the other hand, the response time of PSP is improved by addition of particles. The effect on “mixed” PSP is more apparent than that on “adsorbed”. By fitting the data measured in dynamic tests to multi-exponential functions, it is seen that both types of PSPs have some time-constant components. The number of components are changed by the application method of dye and particle content, but not changed by thickness. Each weight coefficient indicates contribution rate of its corresponding time-constant. Particle content has effect on weight coefficients of both types of PSPs, while thickness has effect only on “mixed” type PSP. From these results, it is expected that the time response of PSP was governed by diffusion of O2 in polymer layer and voids created by particles.

Pressure-Sensitive Paint with Ceramic Particles

To visualize surface flow on a model moving in a wind tunnel, an image-processing technique from fluorescent minituft image has been developed. Unsteady flow region was detected by calculating projected area of minituft. In addition, orientation of minitufts was measured to visualize change of surface flow field. The developed technique has been applied to a slender delta wing undergoing a single-degree-of- freedom rolling motion. A temporal variation of leading-edge-vortex (LEV) breakdown was clearly visualized. Furthermore, change of LEV position by rolling motion of delta wing can be understood intuitively.

Fluorescence Minituft Method, Image Processing

Abstract
An overview of recent experimental results on instability and dynamics of jets at low Reynolds numbers is given.
Round and plane, macro and micro jets are under the consideration. Basic features of their evolution affected by
initial conditions at the nuzzle outlet and environmental perturbations are demonstrated.

Keywords: subsonic jets, hydrodynamic instability, transition to turbulence, flow visualization

ABSTRACT
Results of experimental studies of round and plane propane micro - jet combustion in a transverse acoustic field at
small Reynolds numbers are presented in this paper. Features of flame evolution under the given conditions are
shown. Based on the new information obtained on free micro - jet evolution, new phenomena in flame evolution in a
transverse acoustic field with round and plane propane micro - jet combustion are discovered and explained.

Round and Plane Jets; Acoustic; Flow Visualization; Combustion

In this paper we present the results of PIV imaging performed in the shock tube with rectangular cross-section 24x48 mm. Flat shock wave propagated in the channel with gas flow moving behind it. One PIV image was obtained for each experiment. The non-stationary flow was investigated at the open end of shock tube as well as inside the channel (including experiments at low pressure of 200-700 Torr). The shock tube optical system used observation windows in the low-pressure section of the shock tube, to visualize the shock wave and the flow behind it inside the channel. Instantaneous velocity fields were obtained and analyzed with PIV system on different stages of the flow evolution. Shadow methods and CFD were also used in the investigation.

shock waves, PIV, non-stationary flow

We carried out phase-locked tomographic PIV measurements in a square-shaped, vertically-oriented water tank, in order to understand its general flow behavior and turbulence shear stress distribution in detail. The flow is stirred by a commercially available, three-blade HR-100(1) impeller, with the constant angular speed of 150 RPM. The impeller is mounted at the lower end of a vertical shaft, which is placed along the central axis of the squared cylinder. The corresponding Reynolds number based on the blade's tip velocity and the impeller diameter is equal to 59400.
The present study is a continuation of our previous studies(2),(3) where we carried out phase-locked Stereo PIV measurements in a circular tank with four baffle plates. It is found that as the impeller rotates, it induces a large up-to-down bulk flow in the central region of the tank. Moreover, the blades cutting through the water generates turbulence at the solid-liquid interfaces. The up-to-down bulk motion of the flow convects this turbulence downward, making the turbulence level in the region below the impeller much larger than in the region above the impeller. The blades also induce a vortex at their tips. The turbulence level inside these vortices is much larger than at other locations. As these vortices are convected downward by the bulk flow velocity, it lags behind the blade where it originated, increases in size, and its turbulence level damps down. It leads to the formation of three backward-bended helical arcs, whose one end is attached to the corresponding blade tips, and which increase in size as one traverses towards their free ends. These arcs rotate about the central axis of the impeller with the same angular velocity.
We carried out the present three-dimensional measurements in order to understand the flow characteristics in a greater detail. The phase-locked experiments are carried out in four different vertically oriented, 6 mm thick volume sheets. The central planes of these sheets pass through the impeller's axis of rotation, and they are separated with each other by the constant angle of 30o. We seeded the flow with spherical Nylon tracer particles of average diameter 10μm, and acquired the images using four 1600×1200 pixel cameras. The cameras are arranged at the four ends of the plus shape. In total, we acquired 9000×4 particle image pairs, which would be analyzed by a self-developed GPU program, in order to obtain 9000 three-dimensional instantaneous velocity fields. These velocity fields would be used to obtain some simple turbulence statistics and the nine components of the turbulence shear stress matrix. Afterwards, the maximum turbulence shear stress field inside the flow would be calculated after evaluating the Eigenvalues of the shear stress matrix.

Stirred mixer, Tomographic PIV, Turbulence Statistics, Shear Stress

HILBERT-VISUALIZATION OF VORTICAL AND CONVECTIVE CURRENTS
V. ARBUZOV1,2, Ed. ARBUZOV2, Yu. DUBNISHCHEV1,2, V. NECHAEV2, E. SHLAPAKOVA2
1Kutateladze Institute of Thermophysics
Siberian Branch of the Russian Academy of Sciences,
Russia 630090, Novosibirsk, Pr. Ak. Lavrentyeva, 1
E-mail: dubnistchev@itp.nsc.ru
2 Novosibirsk State Technical University
Russia 630092, Novosibirsk, Pr. K. Marksa, 20.
KEYWORDS: Main subjects: heat and mass transfer, flow visualization Fluid: air, liquid, vortex rings, Rayleigh–Benard Convection, Buoyant Jets Visualization method(s): Hilbert Flow Visualization (HFV) Other keywords: thermogravitational convection, temperature fields
ABSTRACT: The Hilbert–optics methods are successfully applied in experimental hydrodynamics and gas dynamics in problems where it is necessary to visualize the structure of the phase optical density of the medium under study. They are based on the Hilbert filtration of the Fourier–spectrum of the phase disturbances induced in the light field by the vortex structures. The redistribution of energy from the low–frequency area of the Fourier–spectrum to the area of high spatial frequencies is taking place at the Hilbert–transformation. The inverse optical Fourier transformation of the filtered Fourier–spectrum visualizes the phase disturbances of the optical phase density in the medium being studied. Adequate choice of the Hilbert–filter configuration in a combination with structure of the light source allows to adapt methods of the Hilbert–optics for research of the disturbances of the optical phase density in the most various mediums. In particular, shlieren and shadow technologies may be well described in language of Fourier–optics as one of directions of the Hilbert–diagnostics. Various methods of the color Hilbert–visualization of the optical phase disturbances induced in the investigated fluid by vortical currents are considered in the report. The problems of isotropic Hilbert–filtration of any spatial phase structure of the light fields are discussed. The color Hilbert–visualization technologies are analyzed. Results of researches of evolution the complementary vortical rings induced by an impulse of pressure on an aperture under various boundary conditions are presented. Visualization of the Rayleigh–Benard structures arising at thermal gravitational convection in horizontal layers of strongly viscous liquid are performed by methods the Hilbert–optics in reflected light. Other example of application the Hilbert–visualization is research of formation and evolution of floating jets for physical modelling of thermal mantle plumes and subduction zones in problems of global geodynamics. The thermogravitational jets over a linear source can be a model of buoyant flow in the spreading zones. Experiment using models adequated to physical nature should be performed in a relatively short time in contrast to the real slow geodynamic processes. Methods of processing the Hilbert–images allowing to carry out 3D–reconstruction of phase disturbances structures in the investigated fluid on an example of Rayleigh–Benard convection (RBC) are discussed. Application of the Hilbert–visualization in a combination with the method of shift–interferometry has allowed to reconstruct for the first time a temperature field in structures of the thermogravitational floating jets investigated as model of vortical current in the spreading zone.

Main subjects: heat and mass transfer, flow visualization Fluid: air, liquid, vortex rings, Rayleigh–Benard Convection, Buoyant Jets Visualization method(s): Hilbert Flow Visualization (HFV) Other keywords: thermogravitational convection, temperature fields Main subjects: heat and mass transfer, flow visualization Fluid: air, liquid, vortex rings, Rayleigh–Benard Convection, Buoyant Jets Visualization method(s): Hilbert Flow Visualization (HFV) Other keywords: thermogravitational convection, temperature fields Main subjects: heat and mass transfer, flow visualization Main subjects: heat and mass transfer, flow visualization Fluid: air, liquid, vortex rings, Rayleigh–Benard Convection, Buoyant Jets Visualization method(s): Hilbert Flow Visualization (HFV) Other keywords: thermogravitational convection, temperature fields

Precipitations form in clouds, when droplets growing by condensation of water vapour reach a critical diameter slightly larger than 20 µm, above which they can collide and coalesce into precipitation nuclei. In situ characterization of the onset of precipitations with airborne instruments is one of the key issues in cloud microphysics that still remains unanswered because of present instrumental limitations. The main obstacle to the detection of the precipitation nuclei is their relatively small concentration (a few per liter) compared to the one of the droplets (a few hundreds per cm3). Airborne droplet spectrometers, for diameters smaller than 40 µm, rely on light scattering, and for avoiding droplet coincidences, their sampling section is narrow (0.5 mm2), hence limiting the detection of diluted particles, such as precipitation nuclei. Above 40 µm in diameter, droplet spectrometers rely on particle shadowing. Moreover both scattering and shadowing instruments are sensitive to the attenuation of the incident laser light and they require frequent calibration. Recently, attempts have been made to adapt the principle of Phase Doppler Interferometry (PDI) to airborne operations. The main limitation of the system is the requirement for a very accurate alignment of the beams, which is difficult in the harsh environment of airborne operations. The principle proposed in this project for drop sizing is currently referred to as Interferometric Laser Imaging Droplet Sizing (ILIDS). This technique offers a much larger sampling area and provide absolute measurements of the drop size, using interference fringes detection whose frequency is linked to the droplet size with a linear and robust relation. Unlike the PDI technique, ILIDS technique is less sensitive to hostile’s environment.
The objective of this article is to present the development of an airborne probe undertaken within the ALIDS project in the field of the EUFAR network (European facility for Airborne Research) founded by the 7th European Framework Program (2008-2013). It will be focused more specifically on the optimization and the qualification of the ILIDS diagnostic needed for the development of the ALIDS airborne probe. Finally, this article will describe the design process of the optical setup based on the combination of optical simulations and laboratory experiments to define and optimize the instrument under multiple constraints linked to aircraft integration and airborne measurements. Airborne results will be also presented.

airborne measurement, droplet sizing, interferometry, ILIDS

The diffusion-phoresis, which means particle motions induced by asymmetric concentration gradient field [1], provides new strategy to manipulate micro objects (like cells and colloids) in solutions. One example is the autonomous motion of Janus particle (platinum (Pt) coating on one half of a silica particle) due to chemical catalyzed reaction (reduction of hydrogen peroxide) on the Pt surface. Howse et al. [2] and Ke et al. [3] have measured the mean square displacement (MSD) and the effective diffusion coefficient Deff of the self-propelled Janus particles. However, recently it’s shown theoretically that the intrinsic behaviors of Janus particle’s diffusion-phoretic motion can be described by other statistical results rather than MSD [4]. Therefore, we improved the measured technique and image processing method to better track the Janus particle’s motion [5], and we measured the displacement probability distribution [6]. Based on the experiments, we observed three stages of Janus particle movements. Also we calculated the higher displacement moments and compared them with theoretical results [6].

2. Experimental method
The diffusion-phoretic motion of micro Janus particles (ϕ1-2μm) in H2O2 solution was observed by visualization method using a microscope with a 100x/1.40 objective [5-6]. The displacements of Janus particles in di-water and in H2O2 solution with different concentrations (1.25%~15%) were recorded with time intervals Δtint=10ms, 50ms and 100ms respectively. There are three aspects that we made to improve the measurement: (1) limiting the temperature change induced by catalyzed reaction; (2) developing a novel image processing method to determine particle center position with a ±0.5 pixels precision, and thus get particle motion trajectories (Fig.1); (3) increasing the number of tracked particles, and more than 2105 displacements are involved in the statistical analysis.

3. Results
First, we observe a three-stage behavior of the measured MSD: from simple Brownian motion at short times to self-propelled motion, and turns to Brownian-like motion at long times (Fig.2). Secondly, we find that the displacement probability distribution shows double-peaked structure in self-propelled stage at the intermediate time (Fig.3). And finally, we measured the fourth order moment Kurtosis to show the non-Gaussian behavior of Janus particle’s diffusion-phoretic motion, by which the negative peak can be seen clearly. These results present a full illustration of the self-diffusiophoretic motion of Janus micro-particles, and give people a better understanding of its behaviors.

Self-propulsion, Janus particle, particle tracking

The total internal reflection fluorescence microscopy (TIRFM) is an evanescent-wave-based technique for sensitively measuring nanoparitcle dynamics very close to wall. This technique is based on the total internal reflection on the solid-water interface, where a thin layer (~300nm) is illuminated by the evanescent wave[1]. The intensity of the evanescent wave decays exponentially (i.e. I(z)=I0exp(z/zp)), which can provide information of the tracer particle position not just parallel but also normal to wall. Thus, this method has been successfully applied to measure velocity near wall (NanoPIV) [2,3] and also track nanoparticle’s 3D hindered Brownian motion[4,5]. More recently, this technique was extended to some precise measurements of interfacial slip[6]. However, considering the z information is encoded in tracer intensity, it is critical to determine the base intensity I0, so that all tracers’ vertical z position can be known. It has been pointed out that some factors like tracer size variation can significantly bias the z position determination and lead to great error[2,7]. Therefore, characterization the nano-tracer intensity is very important in TIRFM near wall measurement. In this abstract, we proposed a theoretical model considering tracer size variation, tracer concentration distribution and also tracer-wall interaction to build the nano-tracer intensity probability distribution. Our TIRFM near wall experiments showed very good agreement with the theoretical prediction, which means this method is capable to determine the base intensity I0 and thus greatly increase the precision of getting z position.

NanoPIV, intensity probability distribution, TIRFM

Many developed countries have aging societies. Aspiration pneumonia is the third cause of death in Japan and increasing year by year. Thus, in order to maintain the quality of life and extend the healthy lifetime of an elderly person, research on food safety and the mechanisms of swallowing disorders is needed. Swallowing is a very fast and complex action; visually confirming distinctions in swallowing ease for various foods is difficult.

The aim of the present study was to visually clarify the effects of physical food properties on the flow configuration during swallowing.

The originally developed swallowing simulator Swallow Vision® is based on the three-dimensional moving particle simulation (MPS) method and a realistic human organ model that includes information on organ configuration and movement. Swallow Vision® can visualize changes in the configuration of a food bolus as a four-dimensional movie with real-time changes in perspective.

A numerical experiment was carried out by comparing the bolus flow configuration with various food models (i.e., low viscosity with high density, high viscosity, and yogurt properties). In the simulation using a low-viscosity high-density model, aspiration was observed before and after swallowing. With the high-viscosity model, aspiration was observed after swallowing. No aspiration was observed during swallowing using the yogurt model. The yogurt flowed into the pharynx with no splash particles in one mass. This result visually confirmed that yogurt has good physical properties for swallowing ease, which has already reported from several clinical situations. ,Our results here proved that fact by numerical visualization method.

Swallow Vision® can not only visualize the flow configuration of a food bolus but also extract several physical properties such as the velocity, shear rate viscosity, and forces of human organs. This information can be widely applied in actual clinical situations and to develop adequate food for elderly persons and patients with swallowing difficulties and dysphasia.

Moving Particle simulation, aspiration, 4-dimensional swallowing movies, Visualization, velocity, shear rate

In many cases investigation of turbulent combustion, which is a 3D phenomenon, requires measurements of the instantaneous velocity in 3D volume. Developing nowadays volumetric velocimetry techniques, such as tomographic PIV (Scarano 2013, Meas. Sci. Technol.), can provide solution for this issue. However, flow with combustion represents several difficulties for tomographic PIV experiment, such as non-uniform tracer particles concentration, flame and soot luminosity, which reduces signal-to-noise ratio. Moreover, application of tomographic PIV for a large volume is still a challenge due to a lack of laser intensity and images distortions by the flame.
In the present work a laminar premixed axisymmetric (Bunsen) flame was examined as testing object. A set of eight CCD cameras was used to ensure acceptable accuracy and spatial resolution of the tomographic PIV system. The seeding particles were illuminated by the second harmonic of a pulsed Nd:YAG double-head laser (Quantel EverGreen 200) with 200 mJ energy per each pulse. Two mirrors were used to organize multi-pass scheme for the beam. The depth of the illuminated volume was 45 mm with tracer particles in the mixture issued from 15 mm nozzle.
A self-calibration procedure (Wieneke, 2008, Exp. Fluids) was applied to align all camera models by using the experimental particle images and to get a perfect multiple ray correspondence through the measurement volume. The PIV images were processed by a hybrid CPU-GPU reconstruction algorithm with MLOS-SMART (15 iterations) approach. The server station with 2x16 AMD Opteron processors 6274, 2200 MHz (32 cores in total) with the graphics processor NVIDIA Tesla C2075 was used for the calculations. An iterative cross-correlation routine with continuous volume shifting was applied to estimate 3D velocity fields. The final size of the interrogation volume was 543 voxels with 75% overlap factor.
The full paper will contain complete details on the experimental setup, data processing, and obtained results (including non-reacting flow).

tomographic PIV, Bunsen flame, sekf-calibration

A glycocalyx layer coating endothelial cells (ECs) surface of blood vessels, whose thickness were measured to be 20nm - 4.5μm using transmission electron microscopy (TEM), has the important function of keeping the endothelial responsive to changes in vascular fluid dynamics. The layer contains very fine hair-like structures that transmit changes in shear forces to the endothelium, ultimately regulating nitric oxide release. Although the layer may play a key role as a shear force sensing, the mechanism has not been elucidated. To clarify the mechanism, it is important to measure the velocity field near the layer. Therefore, high spatial resolution technique is required to investigate the velocity field around the layer.
In this study, a measurement technique for velocity field near the endothelial glycocalyx layer by utilizing confocal micro-PIV and super-resolution microscopy was developed in order to clarify the mechanism of shear force sensing of the layer. The developed technique was applied to flow near endothelial cells (Normal Human Umbilical Vein Endothelial Cells : HUVECs）cultured in a microchannel of 100µm in height, 400µm in width, 2mm in length. The flow field near the layer was measured three-dimensionally at 250nm resolution in depth direction by confocal micro-PIV technique utilizing 100nm tracer particles coated with polyethylene glycol (PEG) to avoid adhesion on cells.
Furthermore, thickness and position of the layer with Wheat Germ Agglutinin, Alexa Fluor 488 Conjugate were measured by stimulated emission depletion (STED) microscopy, which is one of super-resolution microscopies to realize 80nm in-plane special resolution. The thickness of the layer and height of the cell were 1.33µm and 3.45µm around the center of the cell.
Combining the velocity field and dimension of glycocalyx layer enabled to investigate the effect of glycocalyx layer to surface flow. The velocities near the glycocalyx layer were lower than theoretical values based on Hagen-Poiseuille flow. The results indicate that the measurement technique is useful to investigate the effect of glycocalyx layer on the surface flow.

Endothelial Cells, Confocal Micro-PIV, Glycocalyx, Super-Resolution Microscopy

The technology of pulverized-coal combustion in vortex flow is one of prospective ways to improve efficiency and ecological performance of boiler units for thermal power plants. The vortex transfer appears to be the aerodynamic basis of the entire combustion process in the so-called vortex furnace, the design of which usually comprises the vortex combustion chamber in the lower part of the furnace, the diffuser, and the cooling chamber exited with discharge flue. With this the tangential-injection nozzle is located in the upper part of combustion chamber. A novel modification of this design, characterized by additional tangential-injection nozzle located horizontally at the bottom of vortex chamber, has been proposed earlier [Pat. RF 2042084]. In this dual-nozzle vortex furnace design, the stable swirl flow inside the vortex chamber is formed by two tangential jets released from the upper and the bottom nozzles. The results on the study of 3-D turbulent flow and coal combustion processes in the dual-nozzle vortex furnace have been reported by authors [Anufriev et al., Energy and Power Eng. 5, 2013; Anufriev et al., Tech. Phys. Lett. 39, 2013].
In the presented work the visualization of large-scale vortical structures in the isothermal laboratory model of dual-nozzle vortex furnace has been performed. With this, Lambda2- and Q- criteria [Jeong, Hussain, J. Fluid Mech. 285, 1995; Dubief, Delcayre, J. of Turbulence, 2000] were applied for the eduction of vortical structures from 3-D mean velocity fields obtained in experimental and numerical study. The three-component Laser Doppler Velocimeter “LAD-056” has been used for measurements of velocity field. The experimental flowfield data processing software has been tested on the Burgers’ vortex analytical solution for the Lambda2- and Q- criteria [Chakraborty et al., J. Fluid Mech. 535, 2005]. The numerical simulation of the steady-state 3-D isothermal turbulent flow in the dual-nozzle vortex furnace model has been performed using the differential Reynolds stress turbulence model with linear pressure-strain correlation. Computations have been performed with the use of CFD package FLUENT. To educe the vortical structures from computational results, both the Q-criterion and the ”pressure minimum” criterion have been applied. The V-type vortex core structure inside the vortex combustion chamber of the furnace model has been revealed demonstrating essentially 3-D structure of swirl flow inside the combustion chamber.
This study was supported in part by the Presidential Program of Support for Young Scientists (No.SP-987.2012.1) and the RF President Grant for State Support of Leading Scientific Schools (No.NSh-5762.2014.8).

Swirl flow, structure, vortex furnace, Laser Doppler Anemometry, numerical simulation

Track 8. Aerodynamics

The paper presents numerical research of the aerodynamic configuration with a conical tail part in the form of a truncated cone. Analysis of flow fields and space distributions of the gas-dynamic parameters was carried out. The calculated results and the experimental data are compared. The performed numerical visualization made it possible to elucidate the feature which is associated with the nonmonotonic character of the pressure distribution on the conical tail part.

Main subjects: flow visualization Fluid: high speed flows, flows with shocks Visualization method(s): numerical visualization Other keywords: axisymmetric flow, conical stabilizer (flare), flare semiapex angle

During the flight in the atmosphere, the optical window of an optical dome has to be cooled and supersonic film cooling is one of the economic ways. After traversing through the complex flow field above the window, the optical wave would be distorted by fluctuations in the density field due to the expansion fan, shockwave, mixing layer and turbulent boundary layer, etc.
　　In this paper, the aero-optical aberrations induced by the flow field of an optical dome with or without gas injection at Mach 3.0 were investigated experimentally based on nano-tracer planar laser scattering (NPLS) and background oriented schlieren. (BOS). The model is a double cone with a supersonic gas film injected parallelly to the model’s upper wall. While there is no injection, the slot acts like a backward facing step.
　　Based on NPLS (Nano-tracer Planar Laser Scattering) technique, the density field with high spatial-temporal resolution was obtained by the flow images calibration firstly, and then the optical path difference (OPD) fluctuations of the original light with wavelength of 532nm vertically to the freestream direction were calculated using Ray-tracing theory.
　　Background Oriented Schlieren (BOS) system, which was proposed by G Miere in 2000, is an technique based on the schlieren principle and are used to measuring the density field of flows. Here we develop this technique to optical wavefront measurement called BOS-WT, and employ it on researching the aero-optical effects on supersonic flow around optical dome with injection. The optical path difference (OPD) fluctuations due to the flow field above the optical dome will be carried out under the condition of with or without injection and compared to the results obtained by NPLS.

Supersonic; Aero-optical effect; Nano-tracer Planar Laser Scattering (NPLS); Background Oriented Schlieren (BOS); Optical path difference (OPD)

Three-dimensional (3-D) density distribution of shock wave and vortex were observed by using LICT (Laser interferometiric computed tomography) measurement quantitatively. We have used a diaphragmless shock tube to produce shock waves with high reproducibility. In our previous study, the 3-D density distributions were reconstructed by ART (Algebraic reconstruction technique). However, if the flow fields include an obstacle, projection data have imperfect parts because the laser beam is blocked by the surface of the obstacle. Because of these imperfect parts of projection data, the reconstructed image has the strong artifacts, and it is difficult to investigate the structure of the 3-D flow fields. In this paper SA (Simulated annealing) reconstruction technique is applied to LICT measurement of the shock wave around a rectangular rod to reduce the artifacts caused from a rectangular rod in reconstructed images. Imperfect 2-D projection data are reconstructed to 3-D density distribution by using SA reconstruction technique and ART. In addition, we are studying projection data for SA reconstruction technique. To estimate the projection data of LICT measurement, pseudo-projection data were calculated from CFD (Computed fluid dynamics) phantom for compressible and inviscid flow. The projection angle interval of pseudo-projection data are calculated 5 degrees, 10 degrees and 20 degrees. The projection data are reconstructed to 3-D density distribution from 36 projection data, 18 projection data and 9 projection data. Reconstructed images by SA method are compared with ART (Algebraic reconstruction technique) reconstruction results and CFD phantom. Finally we discuss the artifact in 3-D density distributions which are reconstructed by SA reconstruction technique.

Shock wave, unsteady flow, CT

In a Scanning Electron Microscope (SEM) system, a beam of electrons is transmitted to a sample placed in SEM chamber. Generally, the chamber needs to be maintained at high-level vacuum as from 10^-4 to 10^-3 Pa. Thus, any liquid evaporates aggressively under such high vacuum environment, and SEM has not been used for a flow observation. In our previous study, we have visualized the flow and measured velocity field using ionic liquid between parallel plates in a micro-scale open channel using a SEM [1]. Furthermore, two-dimensional flow velocity was measured by tracking the tracer particles by Particle Tracking Velocimetry (PTV) from the recorded video [2]. In the present study, the goal is to visualize the tracer particles in a closed channel flow where the liquid is flowing under a lid. In general, SEM can observe only the surface of material, so we cannot see flow under a lid. To overcome this problem, we used a thin film through which electron is transmitted as a lid of the channel. The channel was a cavity made on a metal surface, and a lid made of thin film was placed over the cavity. Test liquid used in the experiment was an ionic liquid, which dose not evaporate under high-vacuumed environment. Tracer particles added to the test liquid were Au-coated plastic particle having a diameter of 3 um. In the present experiment, we were not able to measure the flowrate because it was very small. As a result, by using a thin film as a lid of the channel, we were able to observe the tracer particle moving under the lid in a micro-scale flow.

[1] Yasuda, K., Sogo, M. and Iwamoto, Y., (2013): “Flow visualization and velocity measurement in a small-scale open channel using electron microscope”. Measurement Science and Technology, Vol. 24, 027004.

[2] Yasuda, K., Sogo, M. and Iwamoto, Y., (2013): “Visualization and measurement of velocity field in a micro-scale open channel using electron microscope”, The 24th International Symposium on Transport Phenomena, USB memory.

Scanning electron microscope, Ionic liquid, Channel flow, Microflow

The steady state pH of crevice corrosion was evaluated by pH visualization technique using the modified sensing plate. The modified sensing plate was prepared by a spin-dry coating of a pH-indicator solution containing tetraethoxysilane(TEOS) and 3-aminopropyl-triethoxysilane (APTES) to form a strong coating of a pH-indicator on the surface of a transparent plate. To evaluate pH variation around 1, the optimum pH-indicator was selected from the point of view of its responses. The response speed of the modified sensing plate was fast (within 5 min.) and its color varied blue to yellow in the range of pH 2 to 0. Corrosion experiments were conducted using a crevice between SUS316 plate and the sensing plate in 7.0% NaCl solution at +0.25V (vs Ag/AgCl, saturated KCl solution). When the crevice corrosion occurred, the color of the sensing plate at the corroded position varied to yellow, indicating the pH at the corroded position was lower than 1. After 48h corrosion, when corrosion current got stable, the color of the sensing plate still kept yellow. After the experiment finished, the responses of the sensing plate were checked. Both of the response speed and the color variation were same as those before corrosion experiments, showing that the steady state pH in crevice corrosion was lower than 1.

crevice corrosion, pH, visualization, steady state

Climate change due to global warming has tended to bring about big typhoons or local heavy rains, which cause unprecedented amount of rainfall these days. The purpose of this study is to improve drainage performance of the rain gutters installed to a building of stories in order to gather rain water falling on the roof and drain it downward. The experimental setup consisted of a drain gutter, a centrifugal pump, a flowmeter, two water tanks, an upstream valve automatically controlled to keep the water surface level of the upper tank constant, a downstream valve to adjust the flow rate and flow channels connecting these devices. The rain gutter was installed just downstream of the upper tank, which simulated the accumulated water on the roof of the building. Two types of rain gutter were tested, one of which was elbow and the other T-shaped. Each type of rain gutter could be tested with or without air intake, which made it possible to evaluate the influence of aeration. The rain gutter and a part of the flow channels were made of Plexiglass so that the appearance of aeration could be visualized. Flow rate and pressure difference between just downstream of the rain gutter and the atmosphere were measured by using the flowmeter and a monometer, respectively. Quantitative flow visualization was also conducted by using PIV method. The results showed that the flow rate for the T-shaped model was larger than that for the elbow model and that the total pressure loss was therefore smaller for the T-shaped model than for the elbow model. The results also showed that the flow rate was smaller in the aeration condition for both types of models. Flow separation was observed on the corner for both types of models and a vertical vortex was observed for the T-shaped model in aeration condition. PIV measurements could be successfully conducted in the condition without aeration and the results were reasonable. The experimental results mentioned above were instructive and useful for considering the improvement of drainage performance of the rain gutters. Possible ways for the improvement are to change the channel inner shape in order to suppress aeration, to chamfer a corner in order to suppress separation and to install a guide in order to uniform the streamwise velocity distribution.

PIV, Rain gutter, Flow Visualization, Drainage Flow, Flow rate, Total pressure loss

In this study, we proposed a novel pressure-sensitive paint (PSP) technique combining with the heterodyne method to improve the measurement accuracy. In general, the intensity-based PSP measurement is conducted by using an illumination light with a constant intensity. In this method, PSP is illuminated by a modulating illumination light. The resultant PSP emission is the beat signal that results from interference between the illumination light and pressure fluctuation of flow field. This image of the beat signal, captured by a sCMOS camera, is used to deduce the pressure fluctuation by the lock-in scheme. In this method, one can detect only the signal at the frequency of interest, while the signals at other frequencies (noise signals) can be eliminated. As a demonstration of this method, we measured the pressure fluctuations in a resonance tube. The pressure fluctuation distribution was successfully obtained with high pressure resolution of O(10 Pa).

Pressure-Sensitive Paint (PSP)

Understanding the pollutant concentration distribution within an urban canyon is of great importance to improving air quality within them. In the present study, the effect of fetch on the pollutant concentration within a three-dimensional street canyon is investigated by large-eddy simulation.
The computational domain was 6.925 m (x) x 0.75 m (y) x 1.0 m (z). Square blocks of side 7.5 cm (=H) are regularly set on the canyon floor at equal interval of H, and are normal to the wind direction. The streamwise, spanwise and vertical directions were as the x, y and z axes, respectively. The front face of the first blocks was located at x = 4.2 m downwind of the entrance, and the block array consisted of 12 rows in the streamwise direction. The mean wind speed at a height of 8H was 3.0m s−1. The line sources were placed within the first, third, fifth, seventh and tenth canyon. The four tracer gases were simultaneously released by a ground-level continuous pollutant line source placed parallel to the spanwise axis at the canyons.
The results show that the mean wind, the turbulent intensities, and the mean concentration within the canyon reach near-equilibrium state after the fifth to seventh row. Takimoto et al. (2009) indicted that the center of the circulation within the canyon located upstream side, and its shifting toward the downstream side until fifth row. Then it is gradually getting back to the upstream side with increasing the fetch. This transition of the circular is related to the behavior of the flow and pollutant concentration within the canyon. Therefore, the flow and pollutant concentration within the canyon before the fifth to seventh row is affected by approaching flow, but the turbulent flows generated by urban canyon are dominant after the fifth to seventh row.

REFERENCE
Takimoto H.; Sato A.; Michioka T.; Kanda M. PIV measurements on the effects of fetch lengths and atmospheric stabilities on turbulent flow over building arrays, Proc. Physical Modelling of Flow and Dispersion Phenomena, 2009, F.5.1.

Large-eddy simulation, pollutant dispersion, urban canyon

To develop a novel measurement procedure, a cross-sectional velocity profile in a rectangular micro-channel was experimentally measured by micro-MTV (molecular tagging velocimetry). We employed photodissociation of NO2 into NO for the tagging technique, and produced NO was visualized by LIF (Laser Induced Fluorescence). This technique has been applied to external flows; whereas, this study is one of a few trial to apply the technique to internal flows. To check the feasibility of the technique to a micro-scale, a channel with a rectangular cross-section with large aspect ratio was employed as a test section, where the flow can be assumed to be two-dimensional. The cross-sectional velocity profile was measured and verified.

MTV, flow velocimetry, micro gaseous flow

It is a well-known phenomenon that the sphere rotating about an axis perpendicular to the flow is subjected to lateral force, called Magnus force. At the moderate Reynolds number and the moderate spin parameter (SP) which is defined by the ratio of the circumferential velocity to the free stream velocity, the direction of the lateral force changes from usual Magnus force to negative Magnus force.
Previous study, we conducted force measurements at a low turbulent wind tunnel to reveal the region of the negative Magnus force. As the result, the negative Magnus force was observed at Reynolds numbers higher than 53500 and the region of the negative Magnus force coincides with Taneda’s results.
To reveal the phenomena, 2-D PIV measurement near the rotating sphere is conducted at Re=70000 which Re clearly appear the negative Magnus force. The SP is chosen 0.0 (no rotation), 0.3 (normal Magnus force appear), 0.6 (negative Magus force appear), 0.7 (normal Magnus force again).
The following results were obtained from the measurements. When the SP is 0.3, the boundary layer separation is delayed at the accelerated side compared with the boundary layer of the decelerated side. Then the flow comes around behind the sphere from the accelerated side and the wake of sphere inclines toward the decelerated side. Therefore the usual Magnus force appears. When the SP becomes 0.6, the boundary layer of the decelerated side is attached. Then the flow comes around behind the sphere from the both sides of the sphere. The interference of these flows produces the negative Magnus force. When the SP is 0.7, the boundary layer of the decelerated side separates again. Then almost same flow as SP=0.3 is formed. So the Magnus force becomes the positive again.
As the conclusion, the negative Magnus force is caused by the separation and attachment of the boundary layer of the deceleration side.

PIV, Magnus force, wake

We perform the temperature and velocity measurements to clarify effects of inclination angle of a heated plate on natural convection heat transfer enhancement by millimeter bubbles. An experimental apparatus consists of a transparent acrylic tank, a heated plate with uniform heat flux, a bubble generator, a DC power supply, a water-cooled exchanger, and a low-temperature thermostatic bath. Millimeter bubbles are injected from five tubes installed at the bottom of the tank using a tubing pump. The heat transfer coefficient with bubble injection is much higher than that without injection, and the ratio of the heat transfer coefficient with bubble injection to that without injection (heat transfer coefficient ratio) ranges from 3.0 to 5.0. This is due to enhancement of both the transport of the warm liquid toward the downstream region and the mixing of warm and cool liquid. The former results from the bubble-induced liquid entrainment, and the latter is mainly due to the increase in the liquid velocity fluctuation induced by a combination of the bubble motion and the vortex shedding from the bubble interface. Moreover, the significant bubble-induced liquid entrainment and the unsteady vortex occur near the heated wall at higher inclination angle of the heated plate. Hence, the heat transfer coefficient ratio increases with increasing inclination angle of the heated plate.

Natural convection; Heat transfer; Bubble; Multiphase flow; Particle tracking velocimetry

Stepped spillways have been regarded with the development of the Roller Compacted Concrete (RCC) technique due to the low-cost and relatively high-speed construction. They intensify the air entrainment, which significantly dissipate the energy of the flow. This increases the turbulence of flow, and reduces the cavitation risks and dimensions of energy dissipater structures at the downstream of the spillways. Regarding this importance, the present study was conducted with application of numerical methods for investigating the turbulent flow over ogee stepped spillways. For this purpose, the Finite Volume-Finite Difference Method (FV-FDM) was employed for numerical modeling of an ogee stepped spillway physical model belonging to a previous research study. Various parameters over the steps like water surface profile, pressure, and velocity of flow over steps were studied. The perfect conformity of numerical and laboratory results is clearly observed both visually and statistically. Then, steps’ dimensions and geometries were changed and various spillways including smaller, larger, curved, obstacle, and steeped steps (and even a smooth ogee spillway) were simulated numerically. Flow properties were studied more to know the nature of flow turbulence, and then energy dissipation over modeled spillways were obtained. Results were compared with each other to survey the flow over the spillways. Results show that specific forms of steps make the flow more turbulent, reduce the cavitation risk, and dissipate the energy better.

Stepped Spillways, Turbulent Flow, Computational Fluid Dynamics (CFD), Finite Volume Method (FVM), Finite Difference Method (FDM)

Stepped spillways can enhance dissolved air to the flow, which increase the rate of the energy dissipation, and thus reduce the size of the energy dissipater at the downstream of spillways. It decreases costs in addition to increase the speed of construction. Thus, it is essential to know characteristics of the flow over stepped spillways. In this paper, the numerical study was conducted with application of Finite Volume Method (FVM) for investigating the energy dissipation and steps over broad-crested stepped spillways of RCC dams. Laboratory models were simulated in order to verification the numerical model. The perfect conformity of numerical and laboratory results is clearly observed. To extend the numerical models, different geometries of stepped spillways were investigated using various steps’ dimensions and channel’s slop; and then energy dissipations over the spillways were obtained using relevant hydraulic formulation. Results were compared with each other to survey the flow over the spillways, and thus steps’ dimensions and geometry regarding the most energy dissipation rate was interpreted. Furthermore, it has been attempted to train an Artificial Neural Network (ANN) including two layers and entailing one neuron on output layer, as well as investigation of the number of neurons at the first layer, using numerical results to obtain a nonlinear formula for prediction of energy dissipation over the stepped spillways. Consequently, the energy dissipation could be easily computed by having the discharge per unit width over the spillway, the steps’ specifications, and the channel slope’s angle. Eventually, the sensitivity analysis of the energy dissipation against the change of each parameter of the spillways was done in which results indicate the behavior of the energy dissipation rate against investigated parameters well.

Stepped Spillways, Energy Dissipation, Finite Volume Method (FVM), Artificial Neural Network (ANN), Sensitivity Analysis

Despite numerous investigations of the crystallization process, the mechanism of this phenomenon has not been studied in detail.
Previous works of the authors focused on the development and expansion of applications of technique that are based on the phenomenon of frustrated total internal reflection of a wide collimated laser beam. This technique allows you to visualize the distribution of the refractive index of the medium at the interface with the measuring glass prism in the boundary layer thickness of several hundred nanometers. If the experiment provided such conditions that the refractive index, for example, of freezing water, depends only on temperature, then the results of images processing give you the temperature distribution along the boundary layer on time.
The experimental setup was created for experimental investigations of the process of freezing water droplets. As a probe radiation the wide collimated laser beam is used, as a research subject a distilled water droplet (10 ul) is used, as a collant the Peltier element is used in its. Drop was placed between two surfaces - the working surface of the prism and the cooling surface of the Peltier element, so it has a meniscus shape. Images of a reflected from the first interface laser beam were recorded with a digital video camera. Because when the refractive index of water is changing as a result of cooling the reflectance coefficient varies accordingly. Thats why the resulting images provide a clear visualization of the processes occurring in a thin boundary layer of water at this time.
To obtain quantitative data the algorithm for the experimental images processing was designed and realized. The result of its work is the temperature dependence of a boundary layer of water at the time of the crystallization process. In addition, the method allows to visualize the structure of the boundary layer of water, because reflectance from the gaseous phase liberated during the crystallization water is remarkably different from the reflectance of the liquid and solid phases of water. The dynamics of the water boundary layer structure in the crystallization process was obtained at different values of the gap between the surfaces of the prism and the Peltier element.

thin boundary layer, liquid freezing, crystallization, frustrated total internal reflection

A laser-induced shock wave in water is of great importance for many scientific researches and applications such as medical devices. In order to understand it, it is crucial to visualize a laser-induced shock wave and quantify the shock pressure distribution.
The visualization is, however, difficult due to an ultra high velocity (more than 1500 m/s). Moreover, the quantification of the detailed pressure distribution by conventional methods such as a hydrophone measurement is hardly achieved.
In this study, we adopt a background-oriented schlieren(BOS) technique. Its principle is quite similar to the conventional schlieren which utilizes the variation of reflective index of the fluid due to its density gradients. The BOS technique consists of a camera, a background with random dot pattern and a schlieren object (a local density gradient). Its advantages are applicability to high-speed recordings with a simple setup and ability of providing quantitative pressure distribution. We also use an ultra high-speed video camera with up to 5M frame per second and 924×768 pixel array in order to measure successive spatiotemporal evolution of the shock wave. In our experiments, a 6 ns, 532 nm laser pulse is focused through a 10 × microscope objective to a point inside a water-filled pool, where a shock wave generates.
We found that the laser-induced shock wave has non-uniform pressure distribution at the shock front. The local pressure at the region in the direction of laser shot is much higher than that in the perpendicular direction. We observed the shape of the laser-induced bubble after an irradiated laser pulse. The bubble has a spheroidal shape. Thus, a likely explanation is that the bubble grows non-spherically, which causes the non-uniform pressure distribution of the laser-induced shock wave.
In conclusion, we visualized the spatiotemporal evolution of the laser-induced shock wave and quantified the pressure distribution using the BOS technique with an ultra high-speed camera. It is found that the pressure at a laser-induced shock front has the angular variation. Our result might be used for improvement of medical applications utilizing a laser-induced shock wave.

Laser-induced shock wave, angular variation of pressure, Background-oriented schlieren technique, Ultra high-speed recording

Nowadays many scientific laboratories and aerospace research centers have a reasoned interest in developing absolutely new engines so-called “Pulsed Detonation Engines” (PDE) based on the use of detonation for combustible mixtures combustion. PDE is a semienclosed tube which fills up with the combustible mixture, where a detonation wave triggers. Reaction products flowing out of the open tube end at a high speed create the jet thrust. This work describes the features of the deflagration-to-detonation transition at a weak initiation in the pulsed combustor (PC), i.e. the model of the pulsed detonation engine. Also the work presents the evaluation of the possibility and degree of acceleration of the DDT phenomena in the PC. The heptane / air / oxygen mixture is used as a working charge in different fuel / oxidizer ratios.

high-speed and transient phenomena, high speed flows, flows with detonation, pulsed detonation engine, turbulence, thrust

In this study, the photo bleaching characteristics of oxygen sensitive particles (OSP) are investigated by using a high speed imaging technique. The OSPs were fabricated by a dispersion polymerization method and dipping method using porous micro spheres. Two representative oxygen indicator molecules, Platinum platinum octaethyl porphyrin (PtOEP) and Platinum platinum (II) meso-tetrakis (pentafluorophenyl) porphyrin (PtTFPP), were used to make four kinds of OSPs. A ultraviolet-light emitting diode (UV-LED) with a wavelength of 383 nm, a microscope with a 20X objective lens and a high speed camera were adopted to record the decay of phosphorescent intensity of OSPs according to the time. The photo beaching characteristics of the OSPs were compared along the time and power of UV-LED. The dispersion polymerized OSPs have had higher photo stability than the porous OSP, and the PtTFPP- embedded porous OSP was more stable than the PtOEP- embedded porous OSP due to the molecular structural characteristics. It is noticeable that dispersion- polymerized OSP incorporated with PtOEP was more stable than the dispersion- polymerized OSP incorporated with PtTFPP.

Oxygen Sensitive Particles, UV LED, High-speed Imaging, Dispersion Polymerization, Photo-bleaching

The aim of this study is to design, fabricate and test a flapping-wing micro-aerial-vehicle (MAV) which is inspired from the biomimetics. The wing frames of flapping-wing MAV imitate the layout of bat wings with total wingspan of 25.6 cm. The wing area is 156.3 cm2 and the aspect ratio of wing is 4.2. The aerodynamic performance of present flapping-wing MAV is tested with a low speed and low turbulence wind tunnel equipped with a six-component force balance gauge. The tested airstream velocity ranged from 0 to 4 m /s and the wing beat frequency changed from 4Hz, 7Hz, 10Hz, to 12Hz which was tuned with different voltage input to the electrical motor. In addition, the influences of initial attack angle of wings (0o ~ 30o with interval of 10o) on the aerodynamic forces of lift and drag were also conducted in this study.
Experimental results were presented into two parts. The first part was focused on the unsteady low Reynolds number aerodynamic performance of the flapping-wing MAV under various combinations of tested parameters. Both time history and periodic-averaged lift force and thrust force were presented. In order to identify the vortex dynamics on the force generating mechanism, a series of smoke-film flow visualization experiments were conducted. Results showed that there is a multiple vortex system (leading edge vortex, tip vortex, and reverse von karman vortex sheet etc.) around the MAV when the wings is undergoing a cyclical flapping-mode.

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Flapping-Wing MAV, Wind-Tunnel Experiments, Flow Visualization, Lift/Drag Force

In recent years, with the increasing concern about carbon-neutral, research on the production and use of biomass resources is underway. Recently, marine plants conversion efficiency to the carbon neutral is higher than that of the earth plants. The use of marine plants is adapted to attract attention, especially in recent years.
For the purpose of mass production of algae, a research had been conducted on the development of highly efficient production system that utilizes high concentration of carbon dioxide to seawater (CO2-enriched seawater; namely CSW). By using a high concentration carbon dioxide dissolved in large quantities in seawater, it is possible to make more active photosynthesis of seaweed. As a result, the effect of promoting further growth in seaweed had been identified. It is an important point of how carbon dioxide can be absorbed effectively to seaweed, and nutrients in seawater in helping large quantities culture of high-density seaweed at that time. That is understanding of carbon dioxide in the seaweed surface, the mass transfer mechanism of nutrients is essential.
As biomass feedstock; still the red algae (Gracilaria tikvahiae) has a relatively high growth potential among the seaweed, and culture experiments for seaweed Gracilaria was promising as well.
For culturing algae, carbon dioxide additive of CSW (1%, 2%, 3%, 4%) and 5 carbon dioxide additive-free control-dissolved seawater were prepared. As a result, the 1% CSW was the most suitable as the best high concentration of carbon dioxide dissolved in seawater to encourage the growth of seaweed, was confirmed.
In addition, in order to study the effect of current velocity around seaweed on the potential growth of Gracilaria tikvahiae, visualization culture experiments using PIV (Particle Image Velocimetry, particle image method) were performed under different current velocities. By applying laser sheet near the main branch located in the central axis of the seaweed, flow around seaweed could be measured. The images were taken on 120-240 frame per second using a high-speed video camera to shoot. Nylon particles (specific gravity 1.03g/cc) to tracer particles for PIV were used. As a result, the flow rate suitable for seaweed culture promotion was confirmed. In addition, the effect and both inside and outside state of the flow around seaweed branches on the seaweed growth promotion was examined.

Carbon Recycle System, Mass Transfer, Marine Biomass, Particle Image Velocimetry, seaweed

The background oriented schlieren (BOS) technique is one of the visualization techniques that enable the quantitative measurement of density information in the flow field with very simple experimental setup. The BOS requires only a background and a digital camera and it can realize the quantitative measurement of density. If there is density change between the background and camera, background image is captured at image sensor with displacement because of the refraction of the light passing through density gradient. The quantitative density measurement can be realized by evaluating the displacement with image analysis.
The Colored-Grid Background Oriented Schlieren (CGBOS) technique using colored-grid pattern has been proposed and applied to some tests in our laboratory. In this report, measurement result of the shock waves generated by the laser induced cavitation bubble in water and an application of the BOS technique to the shadowgraphy measurement of supersonic flow will be discussed.

Background oriented schlieren, shadowgraph, blast wave

The purpose of this study is to investigate motion of a non-spherical object in water. The object is a grain as a representative of natural shape. Our interest is a motion of the seed in flow. The forces acting on the grain are necessary to understand the motion. We measure directly the drag force acting on the grain model made by 3D printer in steady water flow and observed flow around it to understand what happens. The drag force is measured by the strain gauge glued to a rod which the grain model is attached to. The flow is visualized by using water-solvable dye, halogen lamp and high-speed CMOS camera. We show results at the conference.

grain, visualization, drag force, water tank,

Cardiac and cerebrovascular diseases are related to the influence of arteriosclerosis which would cause cerebral infarction and myocardial infarction, respectively. However, the detailed origin and mechanism of arteriosclerosis has been still unknown. It is currently said that leukocyte rolls over the vascular endothelial cells of blood vessel and subsequently adheres to the vessel wall mediating some receptors in the early stage of arteriosclerosis. Therefore, elucidation of the leukocyte rolling behavior in the blood vessel is extremely important to establish the advanced treatment. So far, direct measurement of leukocyte rolling has not been reported.
In this study, we developed a measurement technique for the rolling behavior of leukocyte flowing in a microchannel which mimicked the blood vessel. As the first step to verify the technique, we measured translation and rotation behavior of a polystyrene particle which has similar size to blood cell in a microchannel. The particle for the measurement of both translation and rotation movements needs to be partially tagged to obtain the detailed location of the particle. In the present study, a composite polystyrene particle in which a non-fluorescent particle was tagged with several fluorescent particles was developed. The non-fluorescent and fluorescent particle has amino group and carboxyl group, respectively. Thus, they can be bonded using a condensing agent of DMT-MM. The size of non-fluorescent and fluorescent particle was 10 and 1 μm, respectively. A typical bonding number of fluorescent particle on non-fluorescent one was 4 or 5. It is easy to visualize the particle including its rolling motion in the microchannel. The channel was made of PDMS and glass substrate. The geometry of the channel was designed with small dimensions (w × h = 100 μm × 130 μm) and fabricated by the standard softlithography. The rolling behavior of the particle was measured by lateral observation technique using a small prism mirror through the PDMS sidewall with a thickness of 120 μm. Based on the trajectory of fluorescent particle attached to big non-fluorescent particle using PTV algorithm, we successfully measured the particle movement with rolling in x-z plane and quantitates both translation and rotation speed of it.

Translation and rotation behavior; Lateral observation; Composite particle

Contact lines are the locations where a gas, liquid and a solid meet. From everyday experience we know that such contact lines can be mobile, for example in the case of a water droplet sliding over a glass surface. However, the continuum description of the flow towards or away from a contact line implies that the forces diverge as one approaches a moving contact line. This fundamental problem is of relevance to many applications, and in particular to the development and application of immersion lithography, where a liquid droplet is positioned between the lithographic optical head and the substrate that moves under it.

To investigate the flow within such an immersion droplet we developed and applied a tomographic micro-PIV system that is capable of measuring the internal flow patterns of a droplet that slides over a glass substrate. This method makes it possible to study the flow instabilities that occur near the trailing edge of a sliding immersion droplet. The experimental data reveal that the flow pattern in the tail of the droplet for an inertial flow can be described with a modified theory for the tail of a droplet in the case of a viscous flow.

Further investigation is performed at the advancing and receding contact lines themselves, utilizing total internal reflection fluorescence (TIRF) microscopy. With this approach it is possible to perform measurements in a very thin region, of the order of 100 nm. This has made it possible to demonstrate the presence of a precursor film. In this film the molecular forces, that is Van der Waals forces, come into play, and it provides a resolution to the fundamental difficulties associated with a continuum description of a moving contact line. TIRF microscopy was used to determine the thickness of the precursor film for both advancing and receding contact lines. The experimental data could be interpreted in terms of a modified theoretical model.

total internal reflection microscopy, tomographic PIV, contact lines

The research on asymmetric vortex flow of slender body at high angle of attack is more popular in recent years, not only for the interest of academic field on aerodynamics at high angle of attack, but also for the engineering area that the modern aircraft and air-to-air missile with slender body are expected to maneuver at high angle of attack.
Until now, most previous studies were to find the source of vortex asymmetry of slender pointed body at high angle of attack. One view is that the asymmetric vortices generated on the slender pointed body at high angles of attack and zero sideslip is due to microasymmetries and geometrical imperfections near the nose. The other view is that the cause of vortex asymmetry is a hydrodynamic instability in the vortex flowfield. But both of the two points cannot explain the large and dramatic changes in the asymmetric flowfield that occur with small changes in the nose. Besides, the random geometrical imperfections of the nose bring in indeterminate results with the same geometric slender body, which makes it difficult to study the asymmetric flow in detail. Deng X.Y. and Wang Y.K. solved the indeterminacy of the experimental data by using artificial micro-perturbation based on the idea that artificial perturbation can be determined.After that they established the physical model of asymmetric vortices and make big progress in asymmetric flow over slender pointed body. But there is a few research works on the asymmertric flow over the slender blunt-nose body at high angle of attack. Some find there is no asymmetric flow over it, while others suggest there is asymmetric flow. The present work is aimed at gaining insight into the asymmetric flow on slender blunt-nose body and making better understanding of the determinacy on asymmetric flow over blunt-nose slender body.
The tests were performed in the closed-loop, low-speed wind tunnel at BeiHang University with the Reynolds's number 1.48e5. The model is a slender blunt-nosed body with the overall length of 1087.5 mm and the aftbody diameter of 66 mm. The blunt nose has 83% bluntness and a length of 21.6 mm.
Several conclusions can be made as follows:
1. The flow over the slender body with blunt nose is asymmetric at high angle of attack.
2. At high angle of attack, there is indeterminacy of flow field over the slender body with blunt nose.
3. Artificial tip perturbation was used on the model and determinate data of side force was acquired. The flow over slender body with blunt nose can become deterministic with artificial perturbation.

Asymmetric vortex, slender body with blunt nose, artificial perturbation, aerodynamic at high angle of attack

According to the recent remarkable advances in miniaturization and precision engineering, the scale of the flow of interest has reduced in size. Therefore, the demand for a measurement method the three-component (3C) velocity field in a microscopic volume (3D) has been increased in order to understand the behavior comprehensively. However, a 3D3C velocimetry for microscale flow has not been fully established due to the difficulties for the measurement that required high spatial resolution, non-invasive even in a microscale fluidic channel and device.
In this study, a novel 3D3C micro velocimetry, named anisotropic defocus particle tracking velocimetry (AD-PTV), was developed by evolving defocus-PTV that determined the depthwise velocity by a defocused particle image. AD-PTV uses a cylindrical lens to obtain an anisotropic particle imaging with an elliptical shape. The distorted particle shape enables us to distinguish the out-of-plane position of the particle. Although some estimation methods for out-of-plane position of the particle from the anisotropic shape were reported, this study suggested a simple but useful parameter to determine the 3D particle location.
The AD-PTV system consists of an inverted fluorescent microscope with a mercury lamp as an illumination source and a single sCMOS camera (8-bit, 45 fps). The objective lens of 20 (dry, NA 0.45 and WD 8.2 mm) and cylindrical lens with the focal length of 700 mm were used. The test channel has a back step; upstream and downstream section has 20 and 43.5 μm in height, respectively. The width of the channel was 2000 μm. The tracer particles were 1.0 μm fluorescent microspheres. The working fluid was ultrapure water. The bulk velocity in the upstream area was 123 μm/s and Reynolds number was 5.5  10-3.
This study investigated the characteristic value extracted from the anisotropic particle image to give us precise particle out-of-plane position. As a result, we reached a simple parameter providing the calibration curve with wider available range rather than the aspect ratio, and then acquired the measurable out-of-plane range of 60 μm, which was five times deeper than the theoretical depth of correlation of the conventional micro-PIV. The measurement results show 3D velocity field in the back step microchannel which fitted well with simulated velocity field. The current measurement uncertainties of in-plane and out-of-plane velocity were ±11.3 and ±8.34 μm/s, respectively.

3D3C velocimetry, particle tracking velocimetry, microfluidics, anisotropic defocus

The noise generated from high speed vehicles, such as high-speed trains and automobiles, can be divided into three sources mainly; engine noise, road noise and aerodynamic noise. The contributions of aerodynamic noise levels of high-speed vehicles are rapidly increased in high speed region. Because of the aerodynamic noise increase to the 6th power of the vehicle speed, but other noise levels usually increase to the 2nd power of the vehicle speed. Therefore, in order to develop low-noise transportation system, aerodynamic noise reduction is one of the most important technical issues for the development of high speed vehicles. One of the reasons of difficulty of aerodynamic noise reduction is hard to identify the noise source distribution. For this reason, measurement and estimation of noise source distribution around vehicle is necessary and important to develop the low noise vehicles.
In this paper we introduce methods for identification of aerodynamic noise source around industrial applications.
First we show the beam-forming microphones array technique which are utilized to estimate the aerodynamic noise source measurement both wind tunnel experiments and actual fields. For example, the array system quantitatively identifies the major aerodynamic noise sources of high-speed train are cavities between the vehicles and pantographs. Moreover it is shown that the tonal noise is radiated from a horn of the pantograph. That is, it is possible to visualize quantitative data; it was possible to make clear the object and direction of developments.
Secondary, since the resent advent of high-performance computers, aeroacoustic simulations including acoustic feedback fields have become tractable. We will show the recent work of aeroacoustics simulations such as the noise from flat plate cascade, cavity tone, pantograph cover and recorder and so on. It is noted that the noise reduction method of providing a partition wall in the interior of the pantograph cover was derived from the visualization results of the noise source of the pantograph cover. This idea based on the noise source identification is applied to the actual Shinkansen train (Doctor Yellow). The sound field of the front grill of an automobile was calculated by the direct aero-acoustic simulation. It reveals that the relationship between the noise level and distance of the plates of the front grille.
We will show in details of the noise control reduction technique using plasma actuators and the prediction of aerodynamic sound using the time-resolved PIV

PIV

Detailed understanding of turbulent combustion phenomena is very important to develop high efficiency combustors which contribute to resolve global environmental issues. In this talk, visualization of turbulent premixed flames by advanced laser diagnostics, which include simultaneous OH-CH planar laser induced fluorescence (PLIF) and stereoscopic particle image velocimetry (PIV), simultaneous double-pulsed CH PLIF and stereoscopic PIV, simultaneous triple plane PLIF and two-color dual-plane stereoscopic PIV and simultaneous time-resolved CH-OH PLIF and stereoscopic PIV. By comparing DNS of turbulent combustion, importance of scientific visualization of turbulent combustion field by the advanced laser diagnostics will be discussed.

turbulent combustion, methane-air mixture, PIV, PLIF, swirling premixed flame, jet premixed flame, simultaneous PLIF and PIV

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