Flow Visualization VI

A surface flow visualization technique was developed that uses colored water as a medium to visualize surface flows over wind tunnel models at supersonic speeds. Wind tunnel tests were conducted with this technique used to visualize surface flows in a rectangular box cavity that was mounted in a flat plate at Mach numbers of 1.50 and 2.16. The results showed that this technique was effective in visualizing the surface flows in the cavity and has produced a unique set of data that has increased the understanding of complex unsteady three-dimensional cavity flow fields.

Salt water modelling and laser-induced dye fluorescence are being used to study gravity current flows. Under specific geometric constraints, the dilution mechanisms of these flows are being analyzed to assess the mixing dynamics.

The well-known technique of flow field measurements by particle tracking (e. g. [1]) in a laser light-sheet has been improved by using a special coding function for the illumination, and by the development of algorithms for the automatic analysis of pictures of the entire flow field. The geometric boundary conditions of the object are taken into account. This technique was first tested under well known flow conditions in a rectangular tube with a ramp and afterwards used to measure the flow field inside a passenger car silencer under steady state conditions.

Not invasive measurements of thermo-fluid dynamics fields is of paramount importance in several microgravity applications. The diagnostic systems used until now are not completely exhaustive for the measurements requested by the scientific community, especially in the field of the Fluid Science.Starting from an overview of existing diagnostic systems for accurate measurements of physical parameters in microgravity experimentation, this paper introduces VIS (Visualisation Integration System), a concept under development to manufacture microgravity diagnostic system tailored to applications to transparent fluids. VIS is a merge between deflectometry and photochromic techniques and allows not invasive temperature and density measurements (beam deflection) as well as two dimensional velocity fields identification inside transparent liquids (tracing methods — photochromic dyes).

Flow visualization studies were conducted on the unsteady flow of heat and fluid in rotating drums resulting from a sudden acceleration/deceleration, both with and without a sudden application of inner surface heating. The drum consisted of an inner cylinder, an outer cylinder, and two circular plates for the side walls. The outer cylinder and side walls were transparent to allow observation. A flexible electrical heater was attached uniformly to the inner cylinder. Water and aqueous solution of glycerin at various concentrations were used as the fluid in the drum. Different methods were employed to observe unsteady recirculating flow: (1) a laser light sheet with double-exposure photography, (2) temperature-sensitive liquid crystal combined with image processing, (3) laser Doppler velocimetry, (4) temperature measurements with thermocouples. The flow patterns and temperature distributions thus obtained were compared with each other.

Velocity profiles of aqueous solutions of Hydroxypropylcellulose flowing in rectangular channels were visualized by means of an electrochemical technique. Isotropic and anisotropic solutions were used. The velocity profiles of the liquid crystalline solution were found to be qualitatively different from those of the isotropic one. In particular, anomalous maxima in the velocity near the side walls were observed.

The instabilities in horizontal layers of viscoelastic fluids heated from below and cooled from above have been investigated by the present authors in earlier papers [1] applying holographic interferometry. It was shown that the critical Rayleigh number Ra_c characterizing the onset of laminar steady two-dimensional Rayleigh-Bénard convection can be increased in viscoelastic polymer solutions as compared to Newtonian fluids. Subject of this paper are the transitions to three dimensional or time dependent stability regions.

This paper demonstrates the applicability of the simple smoke injection method for visualization of secondary flow phenomena caused by such body forces as centrifugal and Coriolis forces in curved pipes and rotating channels. Examples are shown for the following secondary flow phenomena: (1) laminar entry flow in a curved pipe, (2) flow in a 180-degree sharp turn of square duct, (3) instability phenomena in a curved rectangular channel with aspect ratio 10, (4) relaminarization in a helical pipe, and (5) pitch effect on secondary flow in helical pipes. The unsteady nature of the secondary flow phenomena caused by such body forces as buoyancy, centrifugal and Coriolis forces at a higher physical parameter is revealed by flow visualization. The applicability of the smoke injection method in understanding many practical internal flow phenomena up to Reynolds number Re ≃ 5,000 is emphasized.

The flow at each intersection in a flow network is characterized by a collision of two flow streams, which results in complex flow patterns through the downstream holes. The hydrogen bubble method is employed to observe flow patterns and mixing behavior of water in the flow network. It is disclosed that (1) the entrance lengths of both the laminar and turbulent flows are much shorter than those predicted by conventional empirical formulas, (2) intermixing of the ramming flows in the intersection zone occurs in turbulent flow but not in laminar flow, (3) intermixing propagates upstream with an increase in the Reynolds number, (4) the streak lines downstream of the intersection are shifted toward the inner walls, forming long recirculation zones that stretch downstream until the exit with less flow through the other half of the channel, and (5) velocity profiles in stagnation-recirculation zones can be obtained through pulse hydrogen bubble technology.

The flow pattern for the viscoelastic fluid, the power law fluid and Newtonian fluid are simulated using the finite difference scheme. The Denn model is used as a constitutive equation. The influence of non-Newtonian viscosity, Reynolds number, Weissenberg number and the dividing flow rate on the sizes of the recirculation zones is studied. Shear thinning decreases the size of the recirculation zone in the lateral conduit and increases it in the main conduit, whereas shear thickening shows the reverse tendency. The size of the recirculation zone in the lateral conduit decreases with increasing Weissenberg number, and in the main conduit increases with increasing Weissenbrg number. The former agrees with the earlier experimental results, the latter does not agree with it.

Flow visualization was used to study the jet in a erossflow problem in the bifurcating pipe flow of a T-junction. The visualizations revealed a great variety of vortex phenomena and — structures generated by the complex interaction between jet and crossflow. This paper reports on some of these and offers a qualitative insight into the very complicated three-dimensional nature of flow fields in a T-junction.Bifurcating pipe flow, jet in a crossflow. flow visualization, coherent vortex structures, recirculation bubbles

Flow patterns in a symmetric two-dimensional wavy-walled channel were investigated by flow visualizations at low Reynolds numbers and intermediate Strouhal numbers: Re=10–300 and St=0. 008–0.05. For steady flow, we discovered a new flow structure consisting of a regular three-dimensional flow as the Reynolds number exceeds 27.5. For oscillatory flow, the critical value of the Reynolds number at the onset of three-dimensional flow increases with the Strouhal number.

The present paper deals with a flow behavior in an annular- conical passage. During the investigation, two steady states of the flow pattern were observed, that is, the streak flow pattern and the annular- vortex flow pattern.The flow visualization was performed by using paraffin mist. A 1.5 W Argon laser light- sheet and a 500 W photographic flood- light were used as an illumination. The pictures were taken using a video camera and a still camera.

Laser techniques to visualize velocity profile in model blood flows are described. The availability of a laser-induced fluorescence method and a photochromic dye tracer method to get the quantitative information of the detailed velocity field in pulsatile flow through bends, bifurcations and stenoses is shown.

The development of color Doppler echocardiography flow mapping (CDFM) represented a major technological breakthrough in the noninvasive investigation of flow fields in the heart. CDFM displays the spatial distribution of abnormal blood velocities in the heart and has been primarily used for evaluation of valvular régurgitation [1]. However, quantitation of régurgitation by CDFM remains difficult [2].

The results of use of the holographic interferometry for measuring of surface tension, diffusion coefficients, thermal diffusivity of liquid media in capillary are discussed.

The visualization of the jet flowing out of a round nozzle with the diameter d = 20 mm at the velocity Uo =20 m/s has been conducted with the aid of a shear interferometer connected with photo- and cinema-cameras. Transversal acoustic excitation influence on a coherent structure type (at Shs=0. 125-2.5) was considered. Their qualitative and quantitative characteristics were obtained. The laser knife application permitted to obtain vortex generation structures in different jet sections.

During last years the use of whole field velocimetry techniques in fluid flows overlays the limits of single point measurements (HWA, HFA, LDA etc.). The enhancements in image recording and processing gave advantages to optical over classical methods. If the interest is focalized on velocity measurements, several new methods can be employed: Holographic Interferometry [1];Doppler Global Velocimetry (DGV) [2];Particle Image Velocimetry (PIV) [3, 4].

This study has attempted to visualize an air flow in the filling weft yarn process in an air jet loom which consists of a special reed and sub-nozzles. A jet flow from one sub-nozzle and a flow through a reed channel have been experimented by using a hot-wire anemometer and a schlieren method with the carbonic acid gas. It is certified by a hot-wire measuring that an angle of jet issued from a nozzle exit with different shapes is different, and that a flow configuration of the vena contracta at the nozzle exit has influence on the angle of jet. Visualization by a schlieren method suggests that a leakage flow from the channel of a reed greatly depends on the thickness and the density of a special reed, also.

A visualization system that enabled two-dimensional time-resolving concentration measurement was constructed, and was applied to study the mixing process of a free circular jet and a confined planar shear layer. The visualized concentration images were digitally processed and analyzed to get quantitative properties such as mean value, fluctuation intensity and frequency spectra of the mixing layers. The system had been proved to be an capable tool for both visualization of vortical structure and quantitative measurement of turbulent mixing.

The two-dimensional jet flow issuing from the metering orifice of the spool valve commonly used for hydraulic power application is investigated by a experimental and a numerical flow visualization when the valve is instantly opened and closed repeatedly. Flow pattern of the jet flow, pressure distributions and flow forces are discussed.

Formation of the interaction between impulse jet and flat plate was investigated. Flow field between the nozzle and the plate was analized using shadowphotography, interferometry, numerical calculation, piezoceramic pressure pickups and thin-film temperature transmitters.

A flow visualization-based investigation of the transition of planar submerged water jet shear layers at moderate Reynolds number is presented. The development of the free shear layers under low level artificial excitation was captured on video tape by dye injection flow visualization. Despite “clean” initial conditions and the imposition of periodic excitation, examination of vortex trajectories revealed that the flow structure was not strictly periodic but exhibited “jitter” in the vortex roll-up location and subsequent vortex interaction events. This study focuses on this non-periodic character of the flow. Since even very simple nonlinear systems can exhibit chaotic behavior, the flow visualization images were examined for evidence of whether the observed non-periodic behavior could be associated with chaos. The flow visualization frames were utilized to derive return maps enabling examination of the flow visualization images in pseudo phase space. Results indicate that many aspects of the non-periodic vortical motion show evidence of chaos similar to that exhibited by lower dimension nonlinear dynamical systems.

Dye visualization techniques have been used to study the flow structures of a round jet in a cross-flow at a velocity ratio (R=V_jet/U_o) of four. The study has revealed some interesting flow features including a small separation region which occurs just below the upstream lip of the pipe exit and that the jet shear layer rolls up to produce distorted ring vortices which tilt and fold with streamwise distance. These and other flow features are analyzed with the aid of critical point theory.

Fluid flow in fluidics which composed of a jet nozzle, an oscillation inducer and an endblock arranged in one framework, is visualized by smoke in air and by hydrogen bubble in water. It is found that the frequency of the self-sustaining oscillation of the flow is linearly proportional to the fluid velocity at the jet nozzle and that the non-dimensional parameter, the Strouhal number, is almost constant regardless the Reynolds number.

Some investigation results for interaction process of saw-like sound waves of high intensity (160–170 dB) with axisymmetrical subsonic and supersonic jets are presented. Flow and sound waves visualization was performed by the direct shadowgraph method using an impulse source with exposure duration 2*10-7 s. Peculiarities of disturbance emergence and development in a subsonic air jet and in a helium jet under acoustic excitation are considered. It is shown that large-scale disturbances arise on the acoustically excited side of a supersonic jet and the jet radiates directional sound at the frequency of the external excitation (Mach waves).

The experimental investigation directed to visualization method development for fast proceeding processes in the turbulent vortex ring core is carried out. The data obtained support the existence and the possibility of registration of the theoretically predicted separate oscillation modes.

The time-dependent flow structure inside a slender starting vortex, which was bounded in the axial direction either by two solid walls or by a wall and a free surface, has been investigated experimentally in water. Particle traces and the dye-injection method were used for velocity measurements and flow visualizations. Numerical simulations were also carried out in order to identify several mechanisms responsible for the observed phenomena.

The behavior of a necklace vortex and a shedding vortex around a square plate protuberance standing vertically on a flat ground wall where the laminar boundary layer develops were studied using visualization techniques. Three different types of steady necklace vortex system and four different types of shedding vortex would appear against the various values of the Reynolds number and the boundary layer thickness. Furthermore, the interference pattern between the main necklace vortex and the shedding vortex in the wake region was examined.

To visualize the Couette-Taylor flows it is essential to know about various observable singularities from which we shall set out an original device carried at permitting the observation of revolution symmetry flow. The system based on the rotation of a laser beam allows multiple adjustments thus offering a wide range of the exploration of flows. Our first results are set out and discussed on the hypothesis of an even more comprehensive development of the system in the future.

In photograph, paper, and steel industries, some products are made by coating a liquid on a web-shaped base material.In the coating process, the condition of the coating bead affects the coating face. Keeping the coating bead stable is an important task. If we can visualize the shape and flow of the coating bead, we can begin to determine more stable coating conditions. However, the coating bead is very small, spread out along the web and the web moves quickly. Therefore it is difficult to visualize the coating bead.Currently in Prof. Scriven’s group at the University of Minnesota, visualization of the coating bead is being studied. Their method uses a glycerine-water solution, hydrogen bubbles and color dye. The coating types which they have tried are slide coating and slot coating.In our experiment, we tried to visualize curtain coating flow. During curtain coating, the coating bead was less stable than that during slide coating or slot coating, because the coating die is farther apart from the coating bead. Therefore, its visualization needs a more highly clarifying technique. Moreover, we considered the influence of the web under several conditions of the coating bead.In our results, we found some characteristic phenomena associated with the coating bead such as recirculating vortices and changing dynamic wetting lines.

Measurements of triggered turbulent spots have been made in a flat plate boundary layer under zero and adverse streamwise pressure gradients. The paper gives samples of the velocity profiles throughout the spot and perspective views of integral parameters. Variations in disturbance level are displayed using graphics packages which facilitate representation of flow features.

This paper describes on a method to experimentally measure the three dimensional velocity distribution of the airflow in rooms. The velocity is measured at many random points by imaging small ‘weightless’ tracers (i. e soap bubbles with diameters of ca. 3mm) carried by the air stream. The area to be analyzed is illuminated along the direction parallel to the main velocity components (x–y plane) in three colored stripes. Color changes of a particular tracer trajectory delivers information in the third dimension. Visual information of the scene is captured with a still video camera in a timed multi-frame sequence (25 frames) and stored on a video floppy disk. This information in the form of images is subsequently processed in a computer to explore the spatial structure of the air velocity field in the observed air volume and time frame.The length and the direction of the particle trajectory is needed to calculate the stationary velocity field. Each single frame produces a snapshot of the paths of the soap bubbles during 1/8 or 1/16sec. In the sequence shooting mode the camera can capture a total of 25 frames at the maximum speed of 8 images/second. Typically, this short time interval is required to analyze small airflow changes, i. e., deviation from the stationary observation, and experimentally predict the turbulence.

Improved images of the coherent structures inside a turbulent boundary layer are obtained. Digital analysis of these images allows to obtain pertinent quantitative informations on the typical eddies for two values of the Reynolds number.

The concept and operation of a novel device to study two-dimensional flows is presented. A suspended liquid film (soap film) is set to motion in a long frame by using the shearing action of an impinging planar water jet By reshaping the frame’s structure, various shear flows for qualitative (flow visualization) or quantitative (laser Doppler velocimetry) studies can be produced. Several examples of shear flows are presented. It is shown that this device can be a valuable tool in establishing a quantitative experimental basis for two-dimensional flows including wakes, jets and grid-generated flows.

Near-wall streaky structures have been studied in a fully-developed turbulent square-duct flow by using combined dye flow visualization — LDV velocity measurement techniques. The velocity fluctuations are conditioned on the topological properties, such as coalescing and branching, and the transverse locations of the visually-identified low-speed streaks. It is shown that a symmetric pair of counter-rotating quasi-streamwise vortices is associated with one low-speed streak in a statistical sense. However, upstream of coalescing point and downstream of branching point of the low-speed streaks, a single quasi-streamwise vortex is associated with one low-speed streak.

The small scale structure of the scalar energy dissipation rate field ∇ξ · ∇ξ (x, t) in turbulent shear flows is studied using quantitative, four-dimensional, spatio-temporal, laser induced fluorescence imaging of a large Schmidt number conserved scalar field ξ (x, t). Previous work [1-3] has examined the mixing process at the diffusive scale λ_D, and has shown that essentially all of the molecular mixing at Sc ≫ 1 occurs in thin, strained, laminar diffusion layers of the Burgers and Townsend type, in which the internal structure is self-similar. This paper addresses the scalar mixing process at scales between the scalar diffusion limit λ_D and the vorticity diffusion limit λ_v The emphasis is on an approach for quantitatively characterizing certain similarity properties of the canonical patterns into which the scalar energy dissipation layers are arranged by the continual stretching and folding action of the vorticity and strain rate fields in turbulent flows.

The flow and mixing behavior in structures used in static mixers and structured packings are visualized. Results show, that the geometrical parameters of these structures significantly affect the mixing behavior of the flow within these structures. By proper choice of the parameters compact mixers with a homogeneous mixing behavior can be achieved.

An experimental wind tunnel investigation was performed using a 70° sweep delta wing. Flow visualization and surface pressure tests were conducted in order to relate the aerodynamic loads to the vortex flow characteristics for both steady and unsteady cases. For ranges of motion precluding the occurrence of vortex breakdown, quasi-steady behavior was seen. For ranges including very high angles of attack, large unsteady effects were measured. The unsteady breakdown location was then correlated with the unsteady surface pressure data.

An application of helium-bubble technique has been attempted in order to investigate the behaviour of the vortical structures on a delta wing in oscillatory conditions.The dynamic behaviour of the vortex breakdown phenomenon has been analyzed.

Asymmetries in the vortical flow generated by the long forebody of the X-29 aircraft were suspected of causing uncommanded yawing moments at high-angles of attack. A smoke flow visualization technique was used to visualize the forebody vortices and to correlate any asymmetries observed with flight yawing moment data. This paper presents a method of analyzing smoke flow visualization data for comparison with asymmetric aircraft moments or forces. Good agreement was found between the forebody vortex asymmetries and uncommanded yawing moments.

The concept of Moving Surface Boundary-layer Control (MSBC) as applied to two-dimensional airfoils is investigated through a planned numerical simulation program, complemented by wind tunnel tests and extensive flow visualization study. The moving surface was provided by rotating cylinders located at the leading edge and upper surface of the airfoil. The results suggest that the concept is quite promising and can provide a substantial increase in the lift and a delay of the stall. The maximum coefficient of lift realized was around 2. 4, approximately three times that of the base airfoil. The stall was delayed from around 10° to 48°! Application of the MSBC procedure to bluff bodies showed a remarkable decrease in the pressure drag.

In order to have a clear understanding of the flow phenomena that are expected to cause the generation of aerodynamic noise from the elevator car and to examine the effect of car configurations on such flow behavior, flow around two elevator car models, one with a standard type apron and the other with an aerodynamic cover, was studied experimentally. Oil flow pattern technique was used for flow visualization. Distributions of pressure fluctuation on the wall surfaces of the models were also measured using a miniature pressure sensor and the RMS results were compared with the oil flow patterns.

This paper briefly presents some engineering applications of the Fluorescent Mini Tuft Technique (FMTT) by author in recent years. The FMTT can simply, quickly, intuitionally and quantitatively measures and displays the traces, cross section shapes and circulation of a spatial vortex in an ordinary wind tunnel, so it is useful for author to investigate the physical mechanism of vortex flow and many engineering problems.

It is known that full-scale wind tunnel tests on passenger cars are usually carried out with fixed wheels and fixed ground plane and this represents the major difference between the wind tunnel simulation and the road running conditions.In this exercise, the wheel rotation was simulated and at the same time, the floor boundary layer was reduced by using the existing boundary layer suction system.The paper reports results of the investigation carried out around an isolated wheel, both rotating and stationary, with a fixed ground plane.The wheel flow field was mapped by means of a 14-hole probe. Furthermore, new software, developed for the new traversing system, was used to allow the probe to accurately follow the wheel contour.With this technique, time averaged values of pressure, velocity and vorticity were measured and used to map the flow field in proximity of the wheel.Some of these maps are shown in this paper.

Flow phenomena occurring in and around a Savonius rotor have been studied by extensive flow visualizations and by the measurement of pressure distributions on the blade surfaces. Experiments are performed both for the stationary and rotating rotor with and without overlap. Based on the results, the variations of the torque mechanisms due to the effect of rotation and overlap are discussed by examining the flow patterns in and around the rotor and the points of flow separation and stagnation on the blades.

Characteristics of the near wake of the flow around a circular cylinder with and without helical surface perturbations were studied. The tests were performed in a low speed wind tunnel and were conducted at a Reynolds number of 10,000 based upon the nominal cylinder diameter. The helix angle of the perturbations was varied in a range from 11° to 21°. The vortex wake formation length was estimated using smoke wire flow visualization and correlated with hot wire anemometry measurements. The smoke flow visualization was also used to qualitatively investigate the vortex formation process in the near wake.

This paper describes the generation of the Karman vortex street and the change of its vortex shedding due to cooling a circular cylinder submerged in an upward free-stream of air at the low Reynolds number 40–50, by showing streaklines obtained by computations of the time-dependent Navier-Stokes equations with the buoyancy term and flow visualizations using the smokewire methods. The shedding frequency of the vortex generated at the low Reynolds number is different from that in the isothermal wake.

A blockage tolerant test section based on a modified Parkinson’s design allows tests up to Re = 4.3 × 105. A schlieren method is used to visualise boundary and free shear layers emanating from a slightly heated circular cylinder. Colour photographs are presented to illustrate the separation of boundary layers and the breakaway of free shear layers in the range 0.4 × 105 < Re < 4.3 × 105. The shift of the separation point for rising and falling Re exhibited a considerable hysteresis.

Experimental studies on the control of the flow around a circular cylinder were conducted by a new method, setting up a small cylinder in the shear layer near the main cylinder. It was found that a forced reattachment of the shear layer separated from the cylinder was realized. The shear layer reattached onto the rear surface of the cylinder and the flow adhered beyond the rear stagnation point. The results obtained were as follows: The drag of the main cylinder decreased about 20 to 30% and the lift was generated with a value of C_L=1.0.

Most of the engineering structures like buildings normally have either square, rectangular, trapezoidal or triangular cross-sectional shape. It is thus essential to know the aerodynamic loading, both in magnitude and frequency, on prismatic bodies. Some preliminary measurement had been carried out by the authors. The objective of the present paper is to conduct flow visualization to gain better understanding of the flow past prismatic bodies with different cross-sectional shape, which in turn will help the analysis of the experimental data.

Vortex wakes of two parallel circular cylinders in tandem, side-by-side and staggered arrangements are examined by visualization experiments using a towing water tank. The cylinder spacing parameters are expressed in terms of longitudinal (or streamwise) spacing ratio L/d and transverse spacing ratio T/d, where L and T denote two Cartesian components of the distance between two cylinder centers and d the diameter. The flow analysis is generally made from direct observation of the visualization images as they are but, in some cases, complemented by image processing results relating to the estimated values of stream function, vorticity and wake frequency.

It is well-known the dimples on the surface of golf ball increase its flying distance. But the detailed mechanism of flow by dimples has not been made clear. The purpose of this research is to make clear the mechanism of this flow in the case of changing the number and shape of dimples by computation and experiment. As the first stage of this research, this paper deals with the effect of the grooves as modeled dimples that were put on the surface of a circular cylinder. The computation was performed by solving the Navier-Stokes equation using the QUICK method. The grooves were formed in the same shape as a golf ball and the number of dimples is 32. The results by computation of the flow pattern around the circular cylinder with and without grooves showed large difference.

A visualization method — syncronous visualization of flow patterns and correlative physical parameters is introduced. By the principle of image composition the image of flow patterns taken by video cameras and the image representing correlative physical parameters can be combined in composite image which can not only shows the flow patterns at some moment but also can shows syncronously the correlative physical parameters, such as vortisity, shear stress, pressure, force, moment, temperature and concentration etc. It is very useful for researching unsteady flow. As an example, the patterns of a flow past a two dimensional H-shape cross-section and the pitching moment acting on the H-shape cylinder are visualized syncronously. The results show a strong correlation between vortex shedding and fluctuating pitching moment.

As part of a study directed towards the axisymmetric boundary layer on a very long cylinder, the flow over cylinders yawed to the main flow direction has been studied by several methods of flow visualisation.

The 3D effects induced by two symmetric endplates upon the flow around an impulsively started circular cylinder are evidenced and analysed by means of two complementary experimental methods of visualization: dispersed and continuous tracers. The corresponding data are used as references to perfect a numerical process. The two sorts of results are presented as comparative cross and spanwise streamline or streakline patterns visualizing the details of the flow structure; velocity distributions are also deduced. Two values of the Reynolds numbers (1000 and 3000) and of the aspect ratio of the cylinder (5 and 10) have been studied.

When a circular cylinder oscillates transversely in a linearly stratified fluid at rest, the streaked flows are generated alternately along the cylinder axis and each streaked flow follows up a wavy path in the horizontal plane.

A simple visualization technique, which was proposed by present authors, is applied to ellipsoid, where the electrolysis method is extended with painting the phenolphtalein. The technique provides streamline directions even at unsteadiness in liquid, especially shows direction of wall shear stress. The vortical structures normal to or lateral to the ellipsoid surface are obtained. The resultis discussed for the range of incidence angle 20 deg to 65 deg. The results as for the critical angles for the onset of closed separation as high as 60 degrees with existing experiment.

Karman vortex velocimeter and flowmeter by use of laser diode have been developed in our laboratory 1).2). However the effects from such as shear flow, turbulent flow, channel wall and etc. are little known. In fact, the frequency of the Karman vortex in the shear flow which was measured by the method developed in our study was lower than that of the uniform flow. As a result, the value of velocity which was measured by Karman vortex velocimeter did not accord with the value of that which was measured by Pitot tube. This phenomenon have to be removed for the development of the velocimeter. To investigate these phenomena and to improve them, flow visualization was carried out.

The purpose of this study is to design the piles structure by using the holographic theory for wave damping in the desired sea shore region. We shall consider holography as the photographic recording of an interference pattern between two sets of light waves, an information wave and a reference wave. These waves are not always light waves in holography. The real sea wave makes also the interference pattern and we can also apply the holographic theory in sea wave. We can obtain the real and virtual image in front of the hologram and behind the hologram respectively in the optical holography when we illuminate the reconstructive wave to the hologram. When we view these images we consider as if there were the object in the region of these images. We can do the same experience in sea wave and we think as if there was the object in the regions of images and it is comparatively still in these regions. Thus we apply the holographic theory to the wave damping in the desired sea shore region.

The optical method presented here is based on Wollaston biprism differential interferometry using a white light source. It yields high-speed, instantaneous interferograms which directly display the isochoric lines of an instationary, two-dimensional flow. The setup is equivalent to conventional separate-reference interferometric systems, but remains differential since one of the beams — the one used as reference — lies inside the undisturbed upstream flow. The method was used to get instantaneous, high speed displays of the instationary flow around a cylinder placed across the test section.

Flow around two-dimensional rectangular cylinders at high Reynolds number over 104 was visualized by a phase-averaging technique using a tandem type of hot-wire probe. Flow visualization with the aid of a computer was carried out for the cylinders with rectangular section of two different width-to-height ratios. One is a cylinder whose width-to-height ratio is 2. 5, with a mixture of two flow patterns; i. e. a fully separated and a reattached flows around the cylinder, and the other has the ratio of 3. 0 with a periodically (alternately) reattached flow. For the former cylinder, two different flows can be easily separated with a phase-averaging technique. Finally, experimental results distinguish the flows into three modes, and show conspicuous differences among their flow configurations.

The flow field around surface-mounted, square cross-section obstacles of half-channel height placed in a fully-developed, turbulent channel flow was investigated by means of the crystal-violet, oil film and laser-sheet visualization techniques. The results were analyzed for a qualitative description of the flow and for the dependence of various macroscopic parameters (eg. separation and reattachment lengths) on the aspect ratio (i. e. ratio of obstacle spanwidth, W, to height, H). The flow geometries can be classified in two categories, corresponding to aspect ratios greater or less than 6.

An interferometric study has been performed to examine the influence of shape on vortex shedding from quasi-twodimensional prisms at high Reynolds number and high subsonic Mach number. It is found that overall scale of the vortex formation region, which is the space just behind a prism enclosed by the upper and lower separating shear layers, governs the vortex shedding phenomena: As scale of the vortex formation region increases, amplitude and way of the pressure variation with time become larger and more regular respectively, and the pressure spectrum at the fundamental frequency becomes larger, but the fundamental frequency itself decreases.

A square cylinder is one of the most commonly employed shape in the study of the galloping type of flow induced oscillation because most buildings have either square or rectangular cross sections and because the square cylinder is susceptible to both galloping and vortex resonance, thus making the problem complicated and challenging. Many researchers had already carried out measurement on forces and pressure acting on a transversely oscillating square cylinder. Some of the author’s own measurement had been reported in Bearman and Luo [1]. The objective of the present paper is to carry out flow visualization on a transversely oscillating square cylinder to gain more understanding of the flow and make comparison with the author’s own measurement.

This paper describes new methods which can determine quantitatively two-dimensional temperature distributions on a surface and in a fluid from colour records obtained using a thermosensitive liquid crystal material combined with image processing. Application-type experiments have been carried out both to visualise the complex temperature distribution over a cooled surface disturbed by different solid obstacles, and also to investigate temperature and flow patterns in a rectangular cavity for natural convection.

This paper describes the relation between color and temperature of suspensions of thermo-sensitive liquid-crystal particles into water carrier which disperse colored light according to temperature. This suspension becomes often to be used to visualize a temperature field in a liquid qualitatively or quantitatively. Being observed by naked eye, a suspension shows colors of dark-reddish, green, blue, purple and again dark-reddish as temperature increases. These color-plays were quantitatively evaluated using a color-meter, and it was concluded that two dark-reddish colors could be distinguished by the saturation value. Spectra of the colored lights were analyzed using monochrometer and it was concluded that the spectra have no predominant component at the temperatures of both dark-reddish colors within wavelength band of visible light.

This article presents a simple technique for temperature visualization using liquid crystals in the liquid region during the process of cooling and solidification. This method shows interesting timewise evolution of flow and temperature fields, i. e. the process of density inversion for freezing of water and the double-diffusive process for solidification of aqueous solutions.

Recent literature on numerical and experimental analysis of air ventilation systems of different geometrical configurations is reviewed. Application to passive solar systems is emphasized. A modified configuration of the conventional Trombe wall system is presented and comparative simulations are performed. Visualization of the calculation results gives insight into the behavior of the new heating system, pointing out some aspects worthy of further investigation.

A method to measure a 3-D concentration distribution of tracer particles in the airflow through visualization and digital image processing is presented. The tracer particle images obtained in different depths illuminated with a laser light sheet are analyzed synthetically including the effect of ray extinction due to light scattering.

To provide a better understanding of three-dimensional convective flow and for the purpose of a comparison with existing numerical models, two computer aided visualization techniques were developed: analysis of the light colour (hue) which is reflected by liquid crystal tracers suspended in the flow, and stereoscopic observation of tracer paths. They allow non-intrusive measurement of temperature fields and 3-D registration of tracer tracks conveyed with the flow, respectively.

Flow visualization with tracer method has been carried out on laminar natural convection in a vertical fluid layer of water with uniform internal heat generation. A pair of opposite vertical walls was cooled and maintained at constant temperatures respectively, and other boundaries were adiabatic. When the fluid layer was heated both externally and internally, complicated flow pattern was observed. Flow patterns were classified into three types with the internal and external Rayleigh numbers. Similar flow pattern was observed for different aspect ratio.

A finite difference method with a SIMPLE algorithm was applied to numerically handle a two dimensional problem in a compact heat exchanger with louvered fins. The characteristics of physical phenomena for the fluid flow and heat transfer inside a heat exchanger are investigated by changing geometric and flow parameters such as louver angle of the fin(0), the ratio of louver pitch to fin pitch(F_P/L_P) and Reynolds number(Re=UL_p/v). Computational results are graphically visualized and many important physical characteristics could be interpreted from those computational visualization.

An automatic analysis of thermocolor paints is done. All the images have been masked, corrected from non uniform illumination and registered. Then, after having compared different colorimetric representation systems (R-G-B, I-H-S and K-L bases), we use the bidimensional histogram to extract the different colors and so detect the iso-flux lines on each image. A relative thermic exchange map is obtained by superimposing a sampling of processed images.

The influence of geometric and fluiddynamic parameters on local heat and mass transfer is analyzed for different finned tube configurations. A visualization method is used to understand the near wall transport phenomena. The local heat transfer coefficients are quantified by a measuring technique which allows the calculation of the heat flux distributions to optimize heat exchangers.

Different rows of vortex generators are investigated in an open wind tunnel. By means of an absorption method the mass transfer is visualized for different geometries. For specific rows of vortex generators the local mass transfer as well as the pressure drop for different Reynolds numbers are determined.

The flow visualization tests were carried out for enlarged pinarray models using a reacting-dye injection technique in order to evaluate the effects of the pin cross-sectional shape. Measurements on heat transfer characteristic of pin-fin arrays were also conducted. The test results showed a good correspondence between the heat transfer phenomenon and the flow pattern characteristic.

This paper reports on an approach based on lumped models combined with experimental data of the flow resistance coefficient and heat transfer coefficients. Simulations were carried out for the thermal design of a copy machine by use of flow visualization and a personal computer. The calculated temperature values were compared with measured values for several cases. The compared temperatures were for the drum, power supply, and drum ambience. The selected design parameters were the fan casing size, the presence or absence of holes on the base frame, the rate of heat dissipation from the power supply, and so on. The proposed method is proven to serve thermal designers satisfactorily.

In the last decade the good results attained by means of a widespread use of the Infrared Scanning Radiometer (IRSR) in the experimental study of convective heat transfer problems have proved IRSR itself to be an effective tool to overcome several limitations of the standard sensors, both from the measurement and the visualization points of view [1].

Three-dimensional heat flows generally involve difficulties in being visualized with nonintuitive optical methods. In this paper, however, an attempt is made to visualize such flows using a laser holographic interferometry of which measuring light rays are set to be propagated in the stream direction of concerned heat flows. An analysis of the taken interferogram is performed to obtain quantitative values of three-dimensional local temperatures with good accuracy, and a computer aided processing is made to visualize the heat flows.

To measure the spatially- and temporally-resolved temperature and velocity in a transonic turbine and compressor, the laser-induced fluorescence (LIF) method was developed for the flow field with atmospheric pressure. The temperature distribution was obtained from the fluorescence intensity of the seeded iodine excited with an argon-ion laser, and the velocity was measured by the Doppler shift of the spectral peak of the fluorescence.

Temperature distribution, displayed to the two dimensional CRT, of Infrared Light Emitting Diode was measured by Infrared radiometer to visualize the thermal emission mechanism and the temperature under real time condition. The temperature deviation of the LED element and the temperature response time were evaluated numerically by means of the thermal network method. The compare with the measured data is not only useful for estimation of the LED temperature but also applied to the final inspection of the LED after construction under production process.

A new technique for visualization and quantification of local heat and mass transfer is presented. The technique is based on chemisorption of dyes at solid surfaces. The intensity and the distribution of the colour is directly correlated to the transferred mass. With a remission photometer the test samples are evaluated. First results with this new technique are presented for mass transfer in multiple-jet-stagnation flow.

Wavy channels are especially used for the enhancement of heat and mass transfer in heat exchangers, regenerators, catalyzers and membrane moduls. In the concave part of the ducts a flow instability can be observed leading to longitudinal vortices comparable to the Goertlervortices at concave walls or the Dean-vortices in tube flows. The concave-convex walls in sinusoidal wavy channels alternatively enhances and destructs the longitudinal vortices resulting in highly complex flow and transport phenomena.

The heat transfer coefficients at the different profiles (plane, saw-toothed, rippled, rectangular) of the aluminium plate are obtained by means of holographic interferometry. The plate is heated by the moist air. The most convenient profiles have been selected to be used in the recuperator.

The photochromic flow visualization technique was used to study non-isothermal liquid-liquid two-phase flow.

A new experimental method using a high speed video camera associated with an image processing system is presented. Some examples dealing with the use of this system to study the dynamic behaviour of liquid droplets during their transport (turbulent dispersion, influence of coherent structures, …) or wall interaction (rebound, transformation droplet -> film, vaporization, …) are given.

A facility for the investigation of flow structure in a supersonic combustion chamber has been constructed and tested. The side walls of the rectangular combustion chamber model can be moved during the experiment to the alternately expose water cooled stainless steel or quartz windows. Window exposure time is limited by thermal loading restrictions on the windows. A Schlieren system is used for visualization. Results are presented for tests using both hydrogen fuel and with air being injected through the fuel pylons.

Relative OH concentration profiles in the cone section of an atmospheric pressure methane-air flames stabilized over Bunsen burner have been obtained on the laser induced fluorescence arrangement. It has been established that the profile of the OH radical concentration in the pre-flame cool zone has a flattened section and deviates from the calculated dependence expectable on the assumption of purely diffusion process. It has been concluded that the structure of the conical flames in the gravity field differs from those of flat flames. These differences are attributed to the occurrence of flow instability in the pre-flame zone of Bunsen flames.

The purpose of this paper is to demonstrate, how in-cylinder flow analysis by means of laser light-sheet techniques and laser doppler anemometry (LDA) can help to understand the interaction of swirl flow and combustion in a direct-injection diesel engine and thus supports the development of engines with lower fuel consumption and emissions.

Laminar counterflow flames have been used to study a variety of combustion problems, for example extinction conditions and chemical kinetic mechanisms with a review in Ref. [1], and to provide information for flamelet models of turbulent flames [2]. Recently, this flow configuration for turbulent premixed and non—premixed flames has also attracted interest [3, 4] because the velocity field provides a uniform strain rate, a quantity important for flame extinction, and because the simple geometry facilitates theoretical analyses [5, 6]. Mastorakos et al. [4] found that partial premixing improved flame stability and that a spectrum of flames from “pure” diffusion to premixed flames could be established in the counterflow geometry. The present paper is concerned with the appearance of the range of flames that can be stabilised in turbulent counterflowing streams and gives additional information on the consequences of stretching on laminar and turbulent counterflow flames with partial premixing and on the mixing between two turbulent isothermal opposed jets, information relevant to opposed jet combustion. In the next Section, the geometies and the methods used to visualise the flames are described, with the results presented and discussed in Section 3. Finally, Section 4 summarises the more important conclusions.

The oscillation of streamwise vortices resulting from a jet-on-jet impingement in a round duct with dual rectangular side-inlets was investigated using the particle-tracer visualization technique for Reynolds numbers of 2000 to 26000. The results showed that the vortex patterns could be classified into three oscillation modes: clockwise, impingement, and counter-clockwise modes, and the frequency of the mode shift increased as the Reynolds number was risen.

The type and strength of the in-cylinder flow pattern significantly affects piston engine performance in terms of the rate and cyclic variability of combustion. This paper describes a flow visualization study in which the effect of engine stroke on in-cylinder flow is investigated. It was observed that longer stroke produces stronger swirling motion and in most cases a larger vertical (tumble) component of the rotational motion.

The behavior of a roll-up vortex in a cylinder is studied experimentally and numerically. The vortex is visualized by smoke under illumination of a laser sheet and the unsteady velocity field is investigated by means of laser Doppler anemometer (LDA). A numerical solution of the Navier-Stokes equations and a continuity equation by a finite difference method is also presented. The path line of calculated vortex on the piston at Reynolds number (based on a cylinder diameter and the maximum piston speed) of 5,000 corresponds well with that of observed vortex in an engine at a rotation speed of 756 rpm.

An automated shape modeling system that represents an object body by a solid model of polyhedral approximation was developed using multi-directional image inputs. Application to the non-contacting three-dimensional measurement and tracking of the object of irregular and complicated shape such as a tuft and a candle flame is reported. Parameters involved in this analysis are position, velocity, trajectory, acceleration, skeleton of the body. Tracking of a oscillating tuft, a small tracer particle and a candle flame in a draft is presented. This procedure is entirely automatic requiring no annual operation. Spatial temperature distributions in a laminar asymmetric alcohol wick flame and a turbulent propane burner flame were estimated from multidirectional holographic interferometers using computed tomography. Computer graphics of solid models made by Boolean operation on the initially reconstructed distribution models give a comprehensive understanding of the flame structure.

Solid state imaging devices are increasingly replacing conventional photographic techniques in the flow visualization. This paper gives the following examples of visualization and evaluation techniques, which make useof special features of the CCD’s: (i) multiexposure imaging and analysis of droplet oscillations, (ii) local flow vorticity measurement with specially marked tracers, (iii) high-speed imaging during the frame transfer of the device applied to observations of liquid jet instabilities and crack propagation in a pressed coal powder.

To reduce the emission of harmful substances of Diesel engines a detailed comprehension of spray formation is essential. The investigation of injection nozzles is a very important part in this connection.

In the matrix method, unknown values of individual elements constituting a test object are solved by constructing a large scale matrix equation with M-dimension bigger than the number of elements. The method has possibility to provide us mathematically satisfying solutions. However this has never been performed as far as the authors are aware because it requires a big scale, high speed computer, so called super computer and an appropriate solution method for a big scale matrix equation.The present paper deals with the description of the method itself and an example of its verification by sample data and some results from actual turbine blade data taken in a γ-ray CT apparatus.

This paper provides the experimental results of unsteady separated flows on a blunt plate. The measurement was carried out for the case with the Reynolds number 900 by a Fourier transform method for visualization pictures. The Fourier transform method has been improved for the picture with velocity fluctuation by a simple procedure of normalization. Time mean flow variables measured are compared with other computational results and vorticity peak distribution is presented.

The atmospheric transmission large-area analysis system (ATLAS) was developed to characterize smokes/obscurants during U. S. Army field tests. Digital image processing of data obtained from a thermal imager allows a two-dimensional map of transmission through the cloud (in a plane perpendicular to the observer’s line of sight) to be obtained. The ambient (natural) background scene in the imager’s field of view is the source against which the transmission measurements are made. The spatial resolution varies depending on the geometry of the test setup; however, X–Z resolution (Y is along the line of sight) of the order of 0. 5 m is easily obtained. The time resolution is 10 Hz. Conversion of these results to concentration is described and the results presented. The technique can be extended to three dimensions by using tomographic analysis.

In studying the cavitation of an orifice in a pipe, attempts were made to quantify the cavity extent under different conditions. A system was developed to evaluate the cavity extent by binarizing the video-recorded cavitation patterns to obtain black-and-white fractions. With this, the cavity extent can be quantified with high reproducibility by using relatively simple software and instrumentation. This paper describes the process of this image-processing method with some examples to which this method was applied. As conclusion, it has been shown that this simple image-processing method can be a useful tool for quantifying the cavity extent at developed stages of cavitation in the downstream of orifices in a pipe.

The spatio-temporal derivative method for flow field image measurement is well known as a high spatial resolution technique. The governing equations are derived using Lagrange derivative, assuming that the visualized particle image pattern varies smoothly almost everywhere. The authors examine the formulation of governing equation and the brightness function of the flow image in detail, and try to extend this technique to the theory with higher order approximation. The obtained equation can be applied to the case that illumination intensity is not uniform in measurement area.

The velocity distribution in turbulent boundary layer is measured by the data of the distribution of the average counting numbers of photon. The photons of the scattered light of the micro particles included naturally in flow are counted by the two dimensional photoelectric device. The micro particles in flow are illuminated by a laser light sheet. The temperature of flow is measured by also the photon counting of the fluorescence of the fluid included the suitable fluorescent material.

Algorithms for performing a digital whole-field Fourier filtering technique have been developed. The effect of parameters such as filter shape and location, image resolution and particle size on the number and visibility of the whole-field isovelocity fringes was also investigated. Computer generated images were used instead of actual photographs to allow an evaluation of the method. The flow considered in this paper is that of an impinging flow.

This paper describes an application of a new measuring technique; the spatial filtering method based on dynamic image processing and a sequential image data obtained by a high speed video system for measuring the velocity of flowing particle in a circulating fluidized bed(CFB). The particle velocity was too high and the contained particle numbers too many. Therefore, it was very difficult to specify the peak of frequency by spectrum analysis. As a result, we confirmed that it was possible and successful to basically apply the technique for measuring the velocity of fluidizing particle in a circulating fluidized bed.

This paper describes a useful algorithm for searching points on generalized curvilinear coordinate systems, which are used in finite difference methods. With this algorithm one can compute computational coordinates of arbitrary points, whose physical coordinates are given, very fast and precisely. Once the computational coordinates are known, physical quantities at those points can be interpolated from the data of surrounding grid points. Then, this algorithm is applicable to any stage of simulations; integration of Navier-Stokes equation and pre/post processing of the data.

This paper describes several methods of visualizing the vector fields in a flow analysis. A class of computational algorithms determining the structure of vector fields is stated. It is assumed that the visualized results in the vector fields are classified according to certain kinds of expressions for the solution of the following ordinary differential equation: $$\frac{{d{\text{x}}}}{{d{\text{s}}}} = {\text{u}}\,\,or\,\,\omega.$$We pursue the characteristic feature of the equation by expanding around a critical point, and study the topological transitions of vector fields.

Numerical flow visualization of separated flows around oscillating airfoil are conducted by solving incompressible Navier-Stokes equations by a third-order upwind scheme in order to understand the flow structure and mechanism of dynamic stall. The calculated separated region is small in pitching-up process and it becomes large in a pitching-down process. Quite different characteristics of flow patterns between in a pitching-up and pitching-down processes are obtained.

A newly-developed computational method that simulates some of the flow visualization techniques, such as Schlieren photograph in compressible flow experiments is applied to several flow fields. By applying this method to the numerical data from the computational fluid dynamics simulations, same visual output as what is obtained in the experiment can be produced and the computational and experimental results can be fairly compared. Some of the flow features that are observed in the experiment but do not appear in the density contour plots of the computational results appear in the visual output in this method. It is shown that present method allows the correct comparison of the numerical data with the visual output of experiments and is useful for the validation of the computational approach to the fluid dynamics problems. In addition, accuracy and reliability of the present method are clarified by the theoretical evaluation of the assumptions used in the present approach.

Various flows in micro structure have significant influences on the performance of so-called micro machines, the manufacturing processes of semiconductors, and so on. In some cases, such flows are very sensitive to the boundary conditions on the solid wall, namely, the behavior of gas molecule near the surface. In this paper, molecular motions are visualized by the molecular dynamics methods, where the substance is modeled as an aggregate of particles that simulate the molecules. A solid thin film, which is consisted of monatomic molecules, is formed and then a monatomic gas molecule has collide on the surface. The molecular motions are well observed by this visualization and the numerical results reveal that the scattering behavior of the gas molecule is neither specular nor diffuse reflection.

Two methods are proposed for the visualization of the gas molecule motion by Direct Simulation of Monte Carlo method. By the first one, the sizes and diameters of the gas molecules are neglected, and all the positions of the gas molecules are traced. Then, the loci of the molecular positions are visualized by drawing continuously the positions. By the second one, the diameters of the molecules are enlarged into about 107 times, comparing with the real diameters of the gas molecules. Then, the loci of the molecular positions are visualized by drawing sequentially expressions of the molecular positions at an each time step. Therefore the positions are expressed discretely. The motion of the gas moleclues in a computational cell are visualized by the first method. The traced curves are dependent with Knudsen number. With decreasing the Knudsen number, the curves fold a number of times. The rarefied gas flows through a circular tube installed a cicular disk, held perpendicularly and coaxially with the tube are visualized by the second method. Very few molecules intrude into the rear region of the disk. Rarefied gas flows through an thruster nozzle for an artificial satellite are simulated by the DSMC method.

A computational analysis is performed with the use of the method of the Lattice Boltzmann Equation (LBE). The case of a viscous fluid moving in a square duct at low values of the Reynolds number is considered and the calculations are compared with results of theoretical nature. The main characteristics of the new computational technique are also presented.

Particle Tracking Velocimetry (PTV) is an evolving technique for 3D velocity field measurements in an observation volume. When the observation is made from a platform moving with the flow velocity it also yields Lagrangian trajectories of individual particles. It is one of the techniques which can cover the increasing need for measurements in a Lagrangian frame. The principles of the technique have been published in Papantoniou & Maas (1990) and Kasagi & Nishino (1991). Here some recent developments as well as the testing of the tracking scheme on the Kinematic Simulation Inertial Model (KSIM) test flow field will be presented.

With new algorithm of 3-D particle tracking over multiple time steps, the three-dimensional particle tracking velocimetry (3-D PTV, hereafter) system originally developed by Nishino et al. [1–3] was improved in order to achieve higher measurement resolution. It newly includes three laser disc recorders and also an engineering workstation for faster data reduction. The technique tracks fine particles suspended in a flow over two to four consecutive time steps; a particle’s new position, around which a search region for tracking is defined, is estimated from the particle’s motion at the preceding time steps. With the size of the search region statistically optimized, the tracking algorithm is evaluated on the basis of modeled Lagrangian time spectra of velocity fluctuations. A computer simulation is performed to quantitatively evaluate effectiveness of the present particle tracking technique under a condition of nearly isotropic decaying turbulence.

A three-dimensional particle tracking velocimeter (3-D PTV) is applied to the measurement of an air turbulent boundary layer on a flat plate with a free-stream velocity of 4 m/s. To capture particles’ images that are relevant for PTV measurement, a unique illumination technique is developed by using three strobe lamps and a multi-channel signal retarder. Tracer particles used are plastic micro-balloons, whose average diameter and weight density are 50 μm and 36 kg/m3, respectively. Examination of particles’ traceability confirms that they can follow periodic velocity yariation of the surrounding fluid up to 100 Hz, and that the traceability is good enough to resolve streamwise velocity fluctuations under the present flow conditions. Measured turbulence statistics, including the mean velocities, the turbulence intensities and the Reynolds stress, compare reasonably well with hot-wire measurement, previous LDV measurement and DNS data, hence verifying applicability of the present 3-D PTV to the measurement of turbulent air flows. It is, however, found that near wall measurement needs further refinement to deal with adhesion of the particles to the wall.

In the paper the fractional characteristics of the motion of a finite number of solid particles in a fully developed turbulent air flow are presented. The position of particles in space and time form patterns which can be observed by means of computer-aided visualization. By successive digitalization of shots the distribution of the particles in a restricted area a comparision can be made between the correlational dimension D₂ and the fractional dimension D_F. The correlational dimension was derived by estimating the time series by means of which the distribution of particles in a selected segment of space is described. The fractional dimension was obtained using the “Fractional Brownion motion” model of calculation. A qualitative relation between the above described dimensions has been established. which has shown that they are anisotropic. Therefore similarity between methods of forming topological patterns in space, as well as in time, may be supposed. The assumption may also be made that the patterns depend on the characteristics of turbulent flow in the observed process.

A new image processing procedure by using Spectrum-Correlation has been developed to estimate an instantaneous velocity distribution. This has been applied to analyze velocity fields under breaking waves. As in an image-correlation method, this procedure finds out similar patterns from two successive pictures and estimates velocity vectors. The used pictures were taken with very short time lag between them. Therefore the procedure does not require to trace fine particles, and can be applied under various conditions. The processing time for evaluating the velocity distribution with a personal computer is relatively short. To improve the accuracy of the evaluated velocity distribution, a Laplacian filter and a smoothing filter are introduced. The Laplacian filter emphasizes image patterns near the water surface, and the smoothing filter reduces noises due to the flow rotating motions and turbulence.

A two-dimensional particle tracking velocimetry (2D-PTV) based on binary correlation method which has been proposed by the authors before is applied to measure fluctuating flows around two circular cylinders. The experiments are carried out in the three types of tow cylinder arrangements: (a) tandem, (b) side by side, and (c) staggered. Analyzing the pictures of the flows visualized by the hydrogen bubble technique, instantaneous velocity distribution, root mean square (RMS) values of the fluctuating parts of the flows, streamlines and vorticity contours are obtained. From these experimental data the flow mechanism are discussed.

Two new algorithms of three-dimensional binary correlation method (BCM) are proposed for particle tracking velocimetry. The principal part of the method is an algorithm to evaluate a similarity between two local patterns of distributed particles in a three-dimensional space. Introducing a function, which represents a degree of closeness of two particles, the similarity with a reduced consumption of computer resources. Another method compares distributions on a two-dimensional plane by tranforming the coordinates of original patterns. The performances of the methods are examined by computer simulations.

Particle Image Velocimetry is now a well-established, powerful tool for 2-D flow diagnostics. In its most common applications, a thin sheet of laser light illuminates a portion of the flow. A double exposure photograph is taken to record small light scattering particles seeding the flow. The 2-D flow field data obtained by this technique constitute great progress in comparison with single point measurements by conventional anemometry. Opposite to other whole-field techniques like smoke wire visualisation, for example, PIV is a quantitative measuring method. The opportunity to provide velocity data at one instant of time from a large field of view supports studies in the rapidly growing field of non stationary flows. This support would greatly gain, could PIV be extended in two respects: 1.Simultaneous recording over a certain region in depth2.Registration of out-of-plane-components of the velocity vectors.

In the three-dimensional Particle Image Velocimetry, three-dimensional positions of the tracer particles are needed. Because the obtained image is two dimensional, at least two images taken from different angles are used to determine the three-dimensional particle positions. Therefore, the identification of the same particles in both images is needed. Using the VVH method, three-dimensional particle identification could easily be carried out only from two different angle images. The effects of the particle concentration ratio and the image resolution are clarified. Using this method, the three-dimensional velocity vector can be obtained with high accuracy.

Three-dimensional particle tracking velocimetry (3-D PTV, hereafter) is a relatively new measurement technique which can provide information on all three instantaneous velocity components in three-dimensional space. In this paper, the 3-D PTV technique originally developed by Nishino et al. [1] and later improved by the present authors is presented. Three TV-cameras and sophisticated camera calibration are adopted in order to achieve high accuracy and high spatial resolution of measurement The present technique was applied to various fundamental turbulent flows and proved to be reliable and quite effective in both water and air flow measurements. Some examples of the turbulence measurements, e. g., in a fully developed channel flow, a separated and reattaching flow over a backward-facing step, and a flow in a square cross-section duct, are presented.

An alternative particle tracking method for PIV (Particle Imaging Velocimetry) was developed by applying the Kaiman filter. Numerical simulations to track particles in a 2-D cavity flow were performed to investigate the effects of the present method. It was proved that the method can considerably improve the accuracy and the dynamic range of the PIV measurement.

In this paper, we propose a model-based method for estimating the velocities of unsteady viscous 2-D flow from a series of images. The proposed method utilizes the Kaiman filtering technique[1]. The observation equation is constructed by modeling the image as a distributed parameter system[2]. It is possible to construct a dynamic model for the flow by using the FEM(Finite Element Method). However, the resulting model is too complex to apply the Kaiman filtering technique directly. We propose an adaptive Kaiman filter algorithm which includes the identification of the dynamic model from the observed data. Experimental results are presented to show the effectiveness of the proposed algorithm.

The lid-driven cylindrical cavity flows in the laminar region are quantitatively visualized by a new flow visualization method called the digital vector velocimetry (DVV) method. Particle streak images from the particle streak velocimetry (PSV) method are also taken and qualitatively compared with the velocity vector field obtained from the DW method. Because of the convex wall of the test cell, the side view images of the rotating flows are distorted in the radial direction. These optical distortions are analyzed and corrected using calibration curves prepared to recover the original, accurate axisymmetric rotating flow. The DW system provides measurement with subpixel accuracy. The dynamic range of the velocity is expanded using feedback analysis that selects consistent velocity vectors.

A fast algorithm avoiding the calculation of correlation coefficients is applied to the pattern tracking for an airflow measurement. The pattern similarity is defined by the reputation number of the summations of gray level difference between corresponding pixels until the accumulation exceeds a critical value. An example of the sensitivity examination of parameters included are also described.

The correlation method, which is one of the image processing techniques, have been widely used for obtaining velocity distributions from visualized images of flow. The accuracy of this method, which has not been discussed in detail so far, is examined by simulating tracer-particle images of some simplified flows.

The Lagrangian description of the turbulence is the natural approach to the study of all the phenomena in which one want recognize the behaviour of the fluid particles during their motion within the field. A typical example of such phenomena is the pollutants dispersion in the Atmosphere, as the pollutant particles behave as tags of the fluid. The knowledge of the Lagrangian statistics gives a full description of the behaviour of a single particle since it was released from the source; this informations are very useful to calibrate the Lagrangian numerical models of dispersion, based on simulations of time histories of the pollutant particles released from a source (Thomson 1984). In the present experiment, the atmospheric Convective Boundary Layer (CBL), occurring in late morning and early afternoon of the sunny days above a uniform and plain terrain is simulated. Above this layer, a region in which the temperature grows with the height (the Capping Inversion), almost completely avoids the air-mass exchange between the CBL and the overlaying Free Atmosphere (Wyngaard 1985).

The use of a Particle Image Velocimetry (PIV) method (which uses digital cameras for data acquisition) for studying high speed fluid flows is usually limited by the camera frame acquisition rate. The velocity of the fluid under study must be limited to insure that particles suspended in the flow field remain in the camera’s focal plane in successive images. However, the use of digital cameras for data acquisition is desirable to simplify and expedite the data analysis. A method is presented which will allow the measurement of fluid velocities with PIV techniques using two successive digital images and different framing rates, simultaneously. The first part of the method measures changes in the flow field which occur at the relatively slow framing rate of 53. 8 ms. The second part measures changes which occur in the same flow field at the relatively fast framing rate of 100 to 320 μs. The effectiveness of this technique was tested by studying the collapse of steam bubbles, a relatively high-speed phenomena.

An optical method for the discrimination between slow and fast tracer particles conveyed with a flow is proposed. It is based on the dependence of the brightness of a trace from the velocity of the corresponding tracer. The images are captured by a CCD-camera and processed on-line. A practical application to the visualization of low velocity streamlines in a rotating duct is presented. Attempts to develop this technique into a quantitative tool for velocity measurements will be discussed.

A method to produce microcapsules which satisfy the conditions that the specific gravity is unity and the specific heat is very close to that of water is developed. The microcapsule may be a near-ideal tracer of movement of water. It is filled with pure water and covered with a thin film of plastic material of which specific gravity is controlled to unity. The film material consists of polystyrene and ethylene-vinyl acetate copolymer (EVA), of which specific gravities are about 1. 04 and 0. 95, respectively.

The method of full field velocity measurements by means of optical processing of double-exposed patterns of laser speckle or high density particle images obtained by a thin pulsedlight-sheet illumination in the fluid flow seeded by small tracer particles is known as speckle method or high-image-density PIV. This technique is superior to PIV by means of digital image processing in simplicity of processing procedure and applicable rage of velocity. Recent developments of devices for optical processing, such as liquid crystal display, BSO crystal or position sensitive device, are improving the system of velocity measurement by this technique.

A conditional sampling technique has been introduced to Particle-Imaging Velocimetry. The image processing system designed specifically for conditional image sampling which consists of a laser light sheet, a CCD camera, an image processor with a time difference detector allows to extract the image of the settled conditions from consecutive TV frame images. To confirm the availability of this technique, the system has been applied to the flows behind a rotating propeller, and the timeaveraged velocity distributions at four discrete rotating angles of the propeller are measured. The difference of wake structures at each blade angle position was clearly extracted.

A new method for the automatic processing of Young’s fringes obtained from PIV photograph is presented. This processing method is not sensitive to the speckle noise in Young’s fringe image, so that a high measuring accuracy could be obtained, The measuring error of fringe orientation and spacing are less than 0. 5° and 1% respectively. Furthermore, only a less amount of computation is required.

This paper describes the methods for measuring iso-velocity distribution and iso-velocity direction from PIV pattern with a conventional holographic technique. Ring-shaped and rectangular patterns are used as master patterns for making holographic matched filters for iso-velocity distribution and iso-velocity-direction distribution, respectively. The capabilities of these methods are confirmed by model experiments.