Flow around a sphere desending under the gravity in still and viscous fluid were visualized by means of tracer-particle method. And the locations of the sphere were analyzed using two cameras mounted perpendiculary. It is shown experimentally that the sphere desends curvedly in a plane containing the perpendicular axis and the separaton of a vortex-ring are ovserved. And some of the fundamental features were elucidated by these experiments.

View full abstract

The purpose of this study is to make clear the effect of Reynolds number, rotating speed and surface condition on the flow around a golf ball, a tennis ball and a soccer ball, and on the drag and lift force on these balls. Flow visualization and measurement were performed by changing Reynolds number from 4×10⁴ to 1.6×10⁴ and rotating speed from 500 to 2000 rpm. By the results of these experiments, it was found that the dimple of golf ball, the surface fiber of tennis ball and the seam of soccer ball caused to push the separation point toward down stream and decrease the drag force, and to create large lift force when rotation was applied to these balls.

View full abstract

Fluctuations of flow parameters in a jet are generated in the shear layer of the jet boundary as the backpressure is increased. To investigate fluctuations, it is desirable to perform experiments with nonintrusive diagnostic methods. In the present experiments, the laser-induced fluorescence method was used to measure the fluctuations of a low-density axisymmetric argon jet with high spatial and temporal resolution. The acousto-optic modulator was also applied to obtain the cross-correlation function of the fluctuations. With this technique, the statistical characteristics of the jet fluctuations were clarified.

View full abstract

Temporal vapor concentrations in a cylindrical jet were visualized by planar laser light scattering and a two-dimensional detection system. The light scattering signal was amplified about 10% by adding fluorescent dye in the vapor, and the vapor concentration was almost conserved in the visualized region of z/d=5-10. Two-dimensional distribution of the average concentration showed a trapezoid profile near the nozzle and a Gaussian profile in the developed region. The fluctuation intensity distribution showed peaks near the mixing region. Temporal behavior of the cncentration distributions indicated that three-dimensional large eddies existed in the jet, and that the entrainment of the ambient gas occurred by the eddies.

View full abstract

The Laser Speckle Velocimetry (LSV) is one of the most useful method of quantitative visualization of flow fields. However, some techniques in this method are necessary to improve for a wide use. One of these is illumination technique.
We propose a new illumination technique of a observation plane by sweeping of two laser beams scanned by the same face of a polygon mirror scanner. With this method seeding particles in the plane are illuminated by each sweeping beam with short time difference controlled by incident cross angle of two beams to the scanner and also angular velocity of the scanner.
In this report, the characteristics of the dual-beam-sweep laser speckle velocimetry and application results are discussed.

View full abstract

We have proposed a new technique of illumination in a observation plane by sweeping of two laser beams scanned by the same face of a polygon mirror scanner. With this technique seeding particles in the plane are illuminated by each sweeping beam with short time difference controlled by incident cross angle of two beams to the scanner and angular velocity of the scanner. This can be named dual-beam-sweep laser speckle velocimetry.
In this report, measurements of velocity distribution of flow in a T-type branch duct are performed by means of the velocimetry, and the results are compared with numerical results obtained by the finite volume method considering with k-e turbulence model.

View full abstract

Flow characteristics in an offset-fin array was studied by means of flow visualization. When the Reynolds number based on fin thickness t exceeds a critical value, the wake of a fin becomes unsteady, exhibiting wavy or vortical motion. When instability occures in the wake of a fin, the boundary layer and flow characteristics around the downstream fins are affected. It is found that the wake flow instability is strongly dependent on the Reynolds number based on fin thickness as well as on the fin pitch 2S. It is also found that the frequency of discrete vortices varies with a change in Reynolds number, but, more noticeably, varies with a change in the parameter t/2S.

View full abstract

Flow visualization of gas flows in sharp 180-degree turn of a square cross-section duct was conducted using paraffin mist as a tracer. The flow in such a sharp turning duct is characteristic to the cooling passages in gas turbine blades. Visualized results were recorded using both video and 35-mm still cameras. Whole flow structure in the test section was visualized for the Reynolds number between 300 and 900.
It was disclosed that there exists a large scale 3-dimensional flow structure accompanied by a strong reverse flow along the surface of outer corner.

View full abstract

The vortex wake generated behind circular cylinders in side-by-side arangement is investigated by visualization experiments using a towing water tank. The cylinder spacing ratio T/d is varied between 1.0 and 5.0 for the Reynolds numbers ranging from 50 to 500. A special interest goes to the biased flow phenomenon at spacing ratios between 1.4 and 2.0, as well as to the interaction between two pairs of vortex street observed usually for T/d greater than 2.5. Some vorticity measurements are attempted for a detailed flow analysis. The measurement is based on our image processing technique designed for flow visualization using a streak-line method.

View full abstract

Particle dispersion at a right-angled open-channel confluence is simulated by a two-dimensional discrete vortex method. Particle movements due to the unsteady motion of a separation bubble at a confluence are calculated by successively introducing neutral markers at arbitrary points or points in a line and by tracing them. Calculated results concerning a concentration of particles downstream from a point source or the size of a mixing region show favorable agreements with the experiments executed on the surface-flow at the confluence.

View full abstract

Unsteady features of the surface flow at an open-channel confluence were examined by using a correlation method which is one of image processing techniques. In this research, gray level intensities between the centers of respective pixels were efficiently interpolated to improve the accuracy. By applying the improved method, two-dimensional mean velocity and turbulent intensity distributions were obtained with a reasonable accuracy. And the effects of discharge ratios to the time-dependent features of the separation bubble and separated vortices were verified in detail.

View full abstract

The typical flow behaviors within the supersonic air-intake models were visualized by several visualization methods. Here, the results of the oil-flow method for shock-wave/boundary layer interaction flow of the internal channels of the Mach-3 models were presented. Shock-induced saparation, reatachment and foots of the vorticies were visualized. These flow behaviors were affected by strength of shock waves and boundary layer conditions.

View full abstract

The paper presents the flow behaviors within a supersonic air intake. It is redesigned in order to obtain a higher performance at Mach number 3. Flow visualization is made by using a vapor screen technique. A large scale of longitudinal vortices exists at the corner of the cowl surface and side wall due to the interaction of the oblique shock waves with the boundary layer.

View full abstract

An animated flow visualization of the numerical simulation would be effective for the education on the fluid dynamics. In this paper, two examples of the animated flow simulation, which are coded by the BASIC based on the simple analytical methods for the personal computer, are presented. An example is the flow expression by the discrete vortex method for the shear flow, and the other is that treated with the shock tube problem by the simple theory and characteristic method.

View full abstract

GSMAC (Generalized simplified marker and cell) method which is the fast FEM scheme for incompressible flow is applied to two-dimensional heat convection. Natural convection within horizontal annulus and natural convection within a semicircle heated below are numerically investigated. Numerical results of the natural convection within the horizontal annulus are in good agreement with experimental results at Prandtl number Pr=0.71 and Rayleigh number Ra=4.7×10⁴. In the case of the natural convection within the semicircle heated below, interesting unsteady motions of hot thermal plumes are simulated at Pr=9.0 and Ra=1.0×10⁵. Numerical results show that the GSMAC method is effective in order to predict the heat convection problems.

View full abstract

Potential flows can be expressed using complex function. Therefore, these flows can be easily visualized on a personal computer. In the present paper, flow visualization of two potential flows have been carried out by a NEC personal computer system. One is a flow around a rotating ball, and the other is a flow around wings. Results of theoretical of analysis are presented by streamline. Computer program is written by FORTRAN on MS-DOS.

View full abstract

A method of animation for unsteady turbulent flow is developed. In order to show the flow smoothly on a personal computer system, all of graphic data are calculated from measured data at first. These are compressed small enough to display the flow for long period. This process makes possible the computer (PC-9801) to treat more than 500 pictures (160×84 dot, 16 grades) in main memory (640KB).
Applying this method for wave-current combined flow over rippled bed, the spacial profile of Reynolds' stress-u'v' is displayed like as the visualization. Superimposing the mean velocity profile, the negativeproduction of the turbulent energy can be understood visually.

View full abstract

There are many methods to measure wave height at one point. But to know the distribution of wave height in the two dimentional region, it is necessary to traverse measuring poles in all the region and it is difficult to know the instantaneous wave height distribution.
Then we develop the method measuring wave height by means of picture processing. We color water with ink and know the depth of water with the relation between the brightness of water and the depth of it. It enables us to know the instantaneous wave height distribution easily.

View full abstract

It is shown that a groove whose shape is circular-arc has an effect on moving the separation point backward. Flow visualizations are performed by the hydrogen bubble method and the dye injection method. Numerical simulations are also done by the finite difference method. When it is at about 80 degrees, measured from the front stagnation point, the effect is maximum and a closed cavity flow is formed inside the groove. This effect of the groove presented in this study is qualitatively the same as that of the dimples on the surface of the golf balls.

View full abstract

A computer aided flow visualization of the deformation of an elliptic vortex ring was done by three-dimensional discrete vortex filament method. As a result, there exists very interesting flow patterns. In the case of relatively small oblateness of the initial ring, the elliptic ring deforms as the long axis and the short axis change alternately. As the oblateness of the ring increases, the vortex ring deforms more and separates into two rings. In the case of the oblateness of the ring 0.92, for example, the vortex ring deforms and separates into three rings. Numerical results agree well with the experimental ones except relatively large oblateness of the ring.

View full abstract

Owing to rapid development of computing resources, it becomes possible to obtain great number of data in experiments as well as in numerical simulations. Computer graphics have now become an indispensable tool to analyze these numeric data and to grasp complicated phenomena quickly and easily. Interactions and transformations of vortical fields caused by vortex rings are analyzed and visualized from measured velocity fields. Bridging phenomenon which takes place between two vortex rings proceeding side by side was found in this experiment with the aid of computer graphic images visualizing the vorticity fields. It was confirmed that the vorticity patterns and the instantaneous material patterns make different images.

View full abstract

Investigation is made clear on an identification method of a vortex from a circular cylinder by CAFV. The streamlines in coordinates for a cylinder is at rest or moves, the velocity vector, the streakline, the pathline, the vorticity, the isotherm, the timeline, and the isobar for the circular cylinder wake with the Reynolds number 44 and 70 are obtained and discussed.

View full abstract

A new simplified double checking technique has been introduced to reduce the erroneous velocity vectors which are caused by the binary cross correlation method. Using the double checking technique the extension of correlation region as well as the reduction of erroneous vectors are attainable. Moreover, even if fairly small particles are employed, correct correspondences of particles between the first and the second pictures can be obtained. In addition the relation between particle density and measurement accuracy is discussed and the optimum particle density is suggested.

View full abstract

In order to visualize numerical data of CFD results, we developed an animation system. With the system, we show that the appearance of the same flow depends on its visualization methods, e.g., “stream lines”, “streak lines” etc. And we combine and visualize several kinds of data (pressure, temperature, velocity etc.) at the same time to understand better.

View full abstract

Injection molding is a widely used industrial process, which manufactures plastic parts by forcing molten polymer into a cavity followed by solidification. It should be obvious that the flow analysis in the process is very important to design a solid mold and to determine the operational conditions of an injection-molding machine. To this end we developped the finite element-based flow analysis code named “MOLDIA-F”.
In this paper we simulate the molten plastic flow in the process of molding an automobile part by using MOLDIA-F.

View full abstract

A new measurement system of three-dimensional flow velocity vector based on color information was developed. In the system, tracer particles are visualized by using a prism spectrum. Therefore, the color of a tracer particle can determine its position in one direction. In two other directions, the tracer particle can be tracked on the image by using both a correlation mehtod and a particle tracking method. Consequently, a three-dimensional velocity vector is obtained.

View full abstract

A new measurement system of three-dimensional flow velocity vector was developed using a spatio-temporal correlation method. This method needs simultaneously two images observed at a short distance in the flow direction. Each of the two images consists of time series of the frames. A three-dimensional velocity vector is obtained by calculating spatio-temporal correlation between the two images.

View full abstract

An experimental study is performed on the motion of a particle in a two-dimensional curved open channel. Particles different size and geometry are tested in a water-glycerin mixture. A modified dynamics equation is derived, and a new parameter is disclosed which is pertinent to both particle geometry and fluid flow conditions.

View full abstract

The behavior of cavitation bubbles near a solid wall was investigated experimentally and numerically. The motion of laser-produced cavitation bubbles was observed by means of a high-speed photography. Two methods were applied to visualize the phenomena. One is for observing jet formation using a diffused illumination of back lighting with a diffuser and the other is a schlieren technique to visualize shock waves emitted from bubbles. The boundary integral method was also applied to simulate the bubble motion and numerical calculation were compared with the experimental results.

View full abstract

There is an increase in the propagation of phytoplankton in upwelling zones by reason of raising the deep water involved much more nutrient salts to near sea level by wind oncurrent. Therefore, the bottom of food chain will be raised and the fishing ground become well. At the present time, so many researches and developments have been done for artificial reclamation in such zone. Most of the research in the above have treated the homogeneous flowfield but have not taken account of the density charcteristic in such zone. So that, there are so many problems in practial use.
In this paper, flow visualization is treated in order to recongnize the flow puttern around an artifical upwelling structure in the case of accornting stratified flow. The way of flow visualization is dyeflow method of tracer method.
As the results, next points become clear. One is characteristic of flow puttern of artifical upwelling structure in stratified flow. The other is the direction of the developments of these structures in future.

View full abstract

A visualization of internal and external flow in single dwelling model with cross ventilation is conducted in wind tunnel. A fine alumina powder is used as tracing agent and a light sheet obtained by spreading a laser beam is used as a light source.The flow patterns in vertical sections and horizontal sections are photographed with various parameters of opening's position and room numbers in the model. Useful data are obtained for designing the natural ventilation systems through openings in this study.

View full abstract

It is very important to grasp the fluid-mechanial property of a prosthetic valve on the various driving conditions, in order to develop a ventricular assist device (VAD). Therefore, the flow characteristics of a newly designed ball valve which consisted of a silicone ball and a polycarbonate housing was analyzed by means of the quantitative flow visualization technique and was compared with the Bjork-Shiley prosthetic valve (BS-19ABP, spherical). The flow visualization were carried out on the four different flow rate conditions (3.0, 2.0, 1.5 and 1.0 L/min). It was observed that the decrease of the flow rate influenced neither on the maximum velocity nor on the velocity vector distributions of a ball valve in comparison with the Byirk-Shiley valve. Furthermore, even on the low flow rate condition (1.0 L/min), the decreases of the flow velocity and the shear rate, which might cause the thrombus formation, were not observed in the lower part of a ball valve. In conclusion, a newly designed ball valve has the fluid-mechanical property which meets the requirement of VAD.

View full abstract

This paper describes the new digital image processing techniques for measuring concentrations of the smoke particles, which are emitted from a stack. The image processor is calibrated for the linearity of video luminance signals and the shading of video images, using by standard gray scale cards. Wind tunnel experiments are also conducted, and the smoke flows behind a stack are visualized clearly with laser light sheet. A total of 3000 image flames are sampled at intervals of 30 Hz. The relationship between averaging time and video image signals for the smoke flow is investigated. From the experiments, it is confirmed that the averaging time for turbulent video image signals is required to be more than 15 seconds.

View full abstract

In liquid flow, propagating acoustic wave is practically longitudinal wave. When the wave incidents with different angle of refraction at liquid-solid contact surface, transverse and surface wave can be generated in the solid plane surface depending on the angle of incident.
In the experiment of bierfringe method of the flow of boundary layer, the variation of local share distribution can be observed when the surface acoustic wave propagates along the plate.

View full abstract

The hydraulic model experiment for a tidal basin requires a log term flow measurement in wide area, keeping its spatial high-measurement density. To fulfill these requirements, we developed an image processing system. The system installs a optical video disk recorder, A/D and D/A converter with LUT and can record successively four visualized flow images at the same time provided that a proper time interval is given. We use many white plastic balls as floats to visualize flows and require the system to process the float images with a high speed. This image processing is done by the hardware of the A/D and D/A converter which turns over the processed data to the float analysis.
The float analysis adopted here lays stress on unique pairing of floats and requires their coordinates and members around the float to be paired in two scenes at different time. A pairing algorithm is proposed and tested by the experiment data which is obtained in the Seto Inland Sea hydraulic model and covers flows around islands and bay mouths.

View full abstract

Three types of mixing (stratified, partially mixed, well mixed) observed in tidal estuaries are well known. Although its importance for engineering aspects, hydraulical classification is not yet completed because of the lack of knowledge of physical mixing mechanism on density interface by tidal currents. The behavior of unsteady saline wedge and mixing of the interface due to tide are studied experimentally. The large scale and strong mixing are observed and visualized at the flooding tide which may cause partially or well-mixed type. This phenomena is explained to be caused density interface which caused by the interaction tidal currents and density flow from river and progress toward river mouth from the sea. The experimental results such as time variation of upper and lower layer depth, et. al. are also presented and discussed.

View full abstract

Fluid flow in the rotor of a Francis-type pump-turbine was visualized using a water-table model by means of a tracer method and was pictured using a video camera rotating with the rotor. The moving flow pattern was compared with the predicted stream lines based on a potential flow analysis as well as conventional stills. It is demonstrated that a video movie technique is useful to visualize an unsteady flow and a slow motion with a reverse flow especially in a rotating impeller.

View full abstract

A tandem cascade impeller of a small model Francis-type pump-turbine was tested. The unstable flow patterns at close to no-flow condition were visualized using a video camera which rotated with the impeller at two different relative positions, at one of which the S-shape characteristics was disappeared. The influence of the relative circumferential position on the characteristic curve as well as on the flow pattern was discussed.

View full abstract

In this study, to clarify the oil loss mechanism via piston rings, a transparent glass cylinder engine was used. For photographic observation, a high speed camera, a still camera, and a new system by using TV camera with a synchro-flash and a synchro-memory was applied. Moreover, a unique trace method was developed.
Results obtained for this visualization indicated that oil was mainly drawn into the combustion chamber through the gap areas in compression ring joints by high vacuum at engine braking condition and the oil passing over the peripheral surface of the oil control ring was more apparent when the piston rotational movements were greater.

View full abstract

Performances of a binary cross-correlation method (BCCM) are examined and compared to those of a four-sequential-image tracking method using computer simulation method. The ability of finding particle correspondences, correctness of those decisions, and the rate of measured particles are obtained.
As the results, it is concluded that the binary cross-correlation method seems to give reliable and much velocity vectors when the number density of dispersed tracers is high.

View full abstract

Abstract-In this paper, we propose a method to estimate the velocity of moving object from a series of images with respect to the model of it. This model-based measurement is calculated by the Kalman filter algorithm. For an object, if one of its model can roughly be found, we show that the estimation based on Kalman filter algorithm is more accurate and faster than any other methods without a model. In this approach, the model of image sequence dynamics is made up by Distributed Parameter Systems (DPS). By using this method, we can get not only translation but also rotation parameters of the moving object. Some simulation examples will be given to demonstrate the use and validity of this method.

View full abstract

A new video technique to capture particle images has been developed for extension of measurement range of PIV. An image input equipment, which consists of a beam splitter, three prisms, two TV cameras with variable shutters (framing rate 1/30sec) and a camera contoroller, can product two type of streak images from a tracer particle by controlling the exposure of each camera and the shutter timing between two TV cameras. Flow visualization images are captured in this technique which allows determination of both velocity magunitude and direction during short time interval up to 1/10000 sec. The technique can be applied to measure high speed visual image.

View full abstract

The present paper is a note on the correlation method for flow field measurement using image processing. The inference of image quality which depends on shutter speed, exposure and others, on the velocity analisys is examined using 8-bit image data (256 gray levels). It is found that the the using of standerd deviation of the correlation coefficient in the analysis is effective to exlude the error vectors. In this case, the relative largness of the corrlation coefficient is very important. In order to use the gray level value of the image data effectively, a new correlation technique is proposed.

View full abstract

The improvement and compactness of heat exchangers need the technique for fin's heat transfer promotion. Several ideas have been created, for example, setting slits on fins etc.. However, it is impossible that prototypes for all the ideas are produced, and their performance are estimated.
Therefore, we considered the heat transfer characteristics for one fin. In order to investigate them, the surface temperature of the fin, which was heated uniformly by direct current, was measured using a scanning infrared camera. And the heat transfer coefficient was calculated.
It is significant to change the visualization data to the heat transfer coefficient, which is quantitative value, in this study.

View full abstract

Two-dimensional temperature distribution of a heat transfer surface through a plastic permeable wall is measured by using an infrared radiation sensor. Thermoview of an IC package plate array is obtained by measuring the radiosity coefficient of the tested surfce. Steady, unsteady state and local temperature distribution of the package is derived by the remoto-sensing radiometer.

View full abstract

Freezing of superheated water in a rectangular enclosure cooled from below has been experimentally studied. Encapsulated thermochromic chiral nematic liquid crystals were used to visualize the isotherms near 4°C, where the density of water has the maximum value. In the supercooling and subsequent freezing process, mushroom-like vortices appear on the cold wall or the ice surface and grow through the unstable layer showing temperatures below 4°C due to density inversion. Two different critical Rayleigh numbers for the onset of convection were determined for the supercooling and freezing, respectively.

View full abstract

The authors have been studied the method to visualize electric flux by means of a fluid mapper equipment. In this paper, we propose a new method to visualize equi-potential lines in axisymmetric three dimensional electrostatic fields by using an inversible fluid mapper. The inversible fluid mapper is based on a property that the role of a stream function and pressure of fluid mapper can be exchanged each other. This method has the advantage of being able to easily visualize equi-potential lines in complex dielectrics. Therefore, it is concluded that the present method improves the usefulness of fluid mapper.

View full abstract

The electric flux and equi-potential line distribution on a spherical dielectric are visualized to analyze the electrostatic field by means of a fluid mapper method. The method is derived from an inversibility of the fluid mapper for axisymmetric three dimensional fields. The results are agreement with computational results for electric field analysis. It is concluded that present method expands the fluid mapper applications.

View full abstract

This paper describes a new method for visualizing three-dimensional shock shapes around hypersonic vehicles by using an electrical discharge. The method is based on the following ideas : When an electrical discharge is generated across a shock wave, the shock wave can be seen as a dark portion in the electrical discharge. The three-dimensional shock shape can be visualized by taking a discharge photograph in the rear direction of the flow. In this paper, the reasons the dark portion occurs are mentioned theoretically by considering the ionization efficiency and the excitation function versus electron energies in the electric fields generated between a pair of electrodes.

View full abstract

The method for visualizing three-dimensional shock shapes by using electrical discharges has been developed in this paper. The improved method can visualize wide field shock shapes around hypersonic vehicles by using a single electrical discharge. In order to improve the method, a wide and flat electrical discharge shape was considered. To generate such an electrical discharge shape, a pair of point-line electrodes were utilized. Moreover, in the case of the visualization of shock shapes utilizing the pair of point-line electrodes, it was proved that the electric current should be as small as possible.

View full abstract