Coherent Structures in the flow development region of a plane jet were investigated using the technique of flow visualization. For the flow visualization of the cross-sectional view and the three-dimensional view, the methods using fluorescent dye illuminated by a laser light sheet and a halogen light sheet were adopted. It was shown that the streamwise vortex, which has a counter-rotating vortex structure named rib-structure, is formed in the process of the development of the two-dimensional rollup of the instability wave in the flow development region.
Coherent structure in the neighbourhood of reattachment point by the step flow was investigated using the technique of flow visualization. For the simultaneous visualization of the streamwise view and the spanwise view, the methods using fluorescent dye illuminated by laser light sheets. It has developed that the streamwise vortex is appeared in the upper layer of the spanwise vortex, and that the streamwise vortex is caused by the occurrence of the horseshoe vortex. Further, it was observed that the length of the separated region is about seven times of the step height, and that the reattachment point is fairly fluctuated in correspondence with the move of spanwise vortex.
Scattering of toner particles contaminates the inside of PPC(Plain Paper Copier) and degrades copied picture quality. The copier is required to have a structure that prevents particles from scattering and controls air flow. However, as there exist moving elements, exothermic elements and electromagnetic field, air flow and particle behaviour become complicated. In this report, we show a laser using prototype device by which the particle behaviour in a narrow space of developing unit of PPC can be visualized. The optimal design data for space gap were obtained.
The wakes of three car models with different rear shapes were investigated, first with a combination of 9 Pitot-tubes and afterwards with a 2-Dimensional LDV-system. By combination of both data types and utilizing software on a workstation, the data was visualized in form on quasi three-dimensional streamline graphs. These graphs showed a structural correspondence between the vortices of either the fastback shape and the sedan shape, differences only occurred in their location and extent: two opposite rotating longitudinal vortices developed out of the flow around the car body, leaving a relatively small reverse flow area directly behind the car. Comparing these flow fields with that of the wagon-shaped car the wake differs substantially: the longitudinal vortices are almost not existing, whereas a large reverse flow area mainly caused by the underbody flow of the car developed.
When we obtain velocity vectors in two dimensional plane using PTV, we often observe bad path-lines. Because they have an adverse effect on the accuracy of the measurement in flow fields, most of them have been removed frequently. But the removal causes the reduction in quantity of informations. So bad path-lines were classified into some types remarking the shapes. Now we propose to correct the shapes automatically. And the goal of this investigation is to save the trouble of processing and much time of processing.
For PTV measurement in water, it is very impotant to correct the distortion of images due to refraction at the water-air boundary. The issue becomes more serious for three-dimensional PTV in which the optical axes of cameras are set diagonal to a air-water boundary. The correction becomes, though, more difficult in the condition, more precise correction is requested. In this paper, the new method, which enables the strict correction, is proposed. And it is adapted for the stereo-matching analysis.
In this paper, the genetic algorithm applies image processing to a particle tracking technique of visualized flow fields. The fundamentals of this technique are based on that the one-to-one correspondence is found between two tracer particles selected in two image planes by taking advantage of combinatorial optimization of the genetic algorithm. The fitness function controlling reproductive success in the genetic algorithm is expressed by physical distances between the selected tracer particles. In addition the possibility of realizing velocity measurement is examined through the application of this technique to simulated flow fields of computer animation.
A method for measurement of temperature in the rarefied gas flow has been developed. The flow field is visualized by planar laser-induced fluorescence (PLIF) of I 2 seeded in carrier gas. Iodine molecules have many absorption lines in visible region and radiate intense fluorescence. The fluorescence intensity is proportional to the number density in the ground energy level excited by laser beam. This number is temperature dependent, so the local temperature can be decided from the ratio of the fluorescence intensities of two images obtained by laser beams with different wave length. This method allows to image the two-dimensional temperature distribution of the flow field by a laser sheet and a high sensitive CCD camera. In this paper, the optimum selection of two absorption lines in the transition of B3 Π0+u(ν'=43)←X 1Σ+g(ν"=0) is provided theoretically and verified for the temperature measurement of the flow field of a supersonic free jet in which temperature varies drastically.
In this study, the flow fields of interacting two, three or four parallel supersonic free jets are studied by flow visualization using the planar laser induced fluorescence of iodine molecules seeded in the test gas. Centers of orifices are set on a line, tops of a triangle or square. The flow fields are visualized at the plane including the jet centerlines and at the cross sections vertical to the centerlines. The flow field structures are clarified using the many visualized picutures for each geometrical arrangement of the orifices. Especially, three dimensional structures of the flow fields do not tends downstream to the structures to be expected from the arrangement of the orifices.
This study elucidates stability in a cylinder wake at the low Reynolds number by numerical calculation solving the two-dimensional Navier-Stokes equations and the continuity equation. The wake has a bubble and begins to oscillate at Re=6.0-6.5, where Re is the Reynolds number. The bubble is not stable but unstable; the bubble is composed of two asymmetric standing eddies. Since the flow state outside the bubble is steady and symmetric, instability occurring near the rear stagnant point at 6.5≤Re≤6.0 is not transported in the downstream. Since centipedes in the unite streaklines occur in the downstream at 16.0≤Re, instability is transported in the downstream. A change of the centipedes with an increase of the Reynolds number can give a clear insight on a process of the shift of the wake patterns, viz. the centipede flow, the wavy wake, and the Karman vortex street.
Open channel flows in a trench exhibit complex turbulent flow patterns such as separation, reverse flow, or dead water zone. Although the flow in a trench has been studied both experimentally and numerically, its three-dimensional flow structure has not been clarified in detail so far. In this research, the flow is analyzed using the large eddy simulation(LES). The calculated result shows the evolution of vortices and the three-dimensional turbulent flow structure in the trench.
Motor vehicles are employed for both commercial and personal use. Motorization has brought increased traffic volumes, accompanied by a dramatic increase in motor vehicle numbers. This has produced environmental problems specific to regions or cities as well as general global warming. To maintain a stable automotive society to the 21st century and inhibit global warming, there are many requirements incumbent on the transport sector, especialy road transport. This article describes, with the use of a puff model for the calculation of exhaust gas from road traffic in cities, the pattern of exhaust emission and diffusion for five regions in Japan.
To reduce the aerodynamic noise inside a high-speed elevator, flow visualization experiments and numerical simulations were performed and the flow behavior around its model was studied. These flow visualization results led to the understanding that in contrary to upward motion, during the downward motion the flow near the elevator door got accelerated. Based on these results, we mapped the flow pattern around the elevator model.
Wind pressures on a 3-dimensional prism in natural wind were measured with 180 manometers. Displacement of meniscus in each manometer was reduced to wind pressure data through a new measurement system, which the authors developed using VTR and an image processor. The contours of wind pressure distributions on a prism model at every moment were drawn with this system. It has been found that local severe suctions on the side of the prism model were caused by the two types of conical vortices showed in wind tunnel tests.
A few measured examples of three-dimensional flow utilizing the binary-image correlation method have been reported so far. In this paper, authors are going to add a new example, in which three camera-stereo set is employed for measuring coordinates of tracer particles combining a self-collimating technique. A mixing flow in a rectangular water vessel is measured through a side wall of the vessel. The present measuring system is composed of a three-video-camera stereo-set, frame grabbers and a personal computer for analyzing a series of pictures. Not a few false vectors are contained at the first estimation of timewise correspondences of particles, then, at the second step, those false vectors are eliminated by applying thresholding to the values of correlation coefficients.
An image processing system for analyzing aerial flood photographs is constructed using the correlation method. The system, composed of a personal computer and an image scanner, efficiently uses a mouse for improving the human interface. The two-dimensional velocity distributions obtained for the Yodo River represented streaklike velocity patterns near the river-bank, which corresponds well with the surface flow patterns of the photographs.
When a complex three-dimensional (3-D) flow is visualized for flow analysis by a computer graphics in perspective view, it is difficult to perceive the "depth" of image because of its 2-dimensional display on a cathode ray tube (CRT) or in a printed form. To solve the problem, development of 3-D plotting method capable of displaying streamlines or vectors cleary in the air observable by naked eye, is attempted. The 3-D plotting method is realized such that sensitizer is placed at the focal surface of fly's eye lens of 2-dimensional convex microlens array based on the integral photography principle, and a point light source is moved 3-dimensionally according to the image data in the proximity of the lens surface. Result was a wire frame 3-D picture in the form of hard copy film, which renders a real image in the air observable without specific glasses or a CRT.
It is useful in the education on fluid dynamics to show animated computer graphics for some kinds of flows, since they are dynamic phenomena. Therefore the personal computer softwares with animation have been developed in this research. They are able to be shown by a color display, or projected through a liquid-crystal display unit by an over-head projector. They are also able to be projected by a video projector when a video board is contained within the personal computer. Since the computer graphics are effective to visualize clearly only a necessary matter, they are expected to be practically used for engineering education, especially for fluid dynamics.
An example of the simplest desk top presentation (DTPR) is described in this paper. A personal computer of PC-9801 series is used there, which has only 16-color graphics and no sound. Then, it can offer a simple slide show and the speaker has to make his oral presentation on his own. The most important point is the color reduction of photographic images from full 16 million to 16 colors. It can be carried out well by optimizing the color pallet. The next important point is the data format suitable for the slide show. Two graphic data formats, ZIM and MAG, are recommended from the view poits of data compression efficiency and data decoding time.
The concept of "Multi-Media" has become popular in the fields of personal computers, home electronics, and information technologies recently. The possibility of the application of the multi-media to the presentation for academic and business purposes is described in this paper. The necessary conditions of personal computers and peripherals are discussed from the view poits of hardware and software. An example of the integration of text, still graphics, videos, and sounds is shown. As a result, the multi-media can be a very powerful tool for the presentation or communication in general.
Virtual reality technology has been realised by the recent, development of two media-technologies, hyper-media and cyber-media. It is expected to become more important technology both from the scientific field and from the industrial field, not only because it will be used in the various aspects of daily life but because it will produce a powerful effect on the human mind.
An aircraft training Simulator is one of the representative devices which utilize a virtual reality technology. The advacement being made in the real time computer graphics of the recent year make it possible to conduct take off and landing and ground attack and bombing training safely on the ground and in turn the expansion of the applicable training areas have accelerated the improvement in the visual simulation technology. As of this writing, very realistic sceneries can be produced by processing the database which can be construccted from map data and aerial photographs and the simulated real time out-of-the-window visuals are being used on a simulator to conduct a very realistic mission tactics training on the ground. On the other hand, low price game machine visual systems are being used on automobile simulators, and optical disks containing out-of-the-window sceneries from an engineer's seat are being utilized on electrical train simulators, so that these simulators are used to train operators for safe driving and to teach what to do after an accident occurs.
The KANSEI (human sensitivity) is known as an influential factor in the value judement recently, and it is important to consider the design approach from the viewpoint of physiology, psychology, and human engineering. We call this approach "KANSEI Engineering", and regard as an effective way for designing products also. On the other hand, the progress of computer technologies enable us to experience the Artificial Reality, which perceives our otions and stimulates us with realistic images, sounds, vibrations, etc. Because this Artificial Reality helps to realize much sensational simulations, we propose "KANSEI Simulator", which utilize the Artificial Reality techniques and conventional simulation techniques, as proctical tools of the "KANSEI Engineering". In this paper, we describe the "KANSEI Simulation" and show some examples : a car styling design simulator, a car driving simulator.
The collison of N2 molecules in which only rotation of molecules is regarded as internal degree of freedom is simulated and the energy transfer between translational and rotational energy is investigated numerically at low temperature. The results are visualized and it is shown that energy transfer changes by the direction and orientation of rotational vector and the impact parameter and it is also distributed in some form according to the initial translational and rotational energy. Using these results, the collision model of diatomic molecule is constructed and is applied to the Direct Simulation Monte Carlo Method and some properties of fluids, for instance, the energy distribution at equiliblium condition and so on, are calculated for making sure of its validity. It is shown that the collision process of diatomic molecules can be calculated well by use of this model.
A method by which to transform quantities of an atomic model to those of a continuum one, and vice versa has been proposed. The method is based on an idea that displacement at a point in a continuum model should be a weighted mean of those of surrounding atoms in the corresponding atomic model, while stress values should have the inverse relation so as to preserve strain energy between the two models. The continuum model is then discretized by the Finite-Element Method so that matrix equations for the transformation are derived. These equations have been applied to the results of atomic-model-based simulation of nanoscale cutting to evaluate the stress and strain distribution in nanoscale cutting. The results show that the strain distribution is not very different from that of macroscale cutting but that there is almost no concentrated shear stress in the primary shear zone in nanoscale cutting.
Huge amount of information about velocities and locations of individual molecules is derived in the molec-ular dynamics calculation. On the other hand it is difficult to understand from these results how molecules behave. The authors have been studying about microscopic structure of water in a wide range of temperature and density, including liquid-gas coexistence region and near the critical point. The motion of 256 water molecules in a cubic cell is analyzed by molecular dynamics calculations. Visualization of molecules' location and animation of molecules' motion are successfully performed in the present report to see how molecular structure is formed.
Rarefied gas flows through a channel or a circular tube were simulated by direct simulation Monte Carlo method (abbreviated to DSMC method, hereafter). Solid walls with condensation are installed in the flows. The motion of gas molecules are visualized by the numerical results of the DSMC method. The transimision probability of gas molecules through the circular tube with the ratio of length to diameter, 1, arn almost 39% even if the inner wall of the circular tube are a perfect condensation wall.
The principle and signal-processing method of generalized near-field acoustical holography (GENAH) to visualize the vibration of radiating surface are described. While the conventional acoustical holography is based on the acoustic pressure in far field, GENAR on that in near field. Much higher completeness of transformation of the measured field pressure to the surface vibration is then achieved by back-propagating evanescent waves in near field onto the surface. GENAH signal-processing utilizes the K-space analysis on the basis of the spatial Fourier trans-form, and it is able to "visualize" the correspondence between theory and experiment on vibroacoustical problems. As a specific example, it is illustrated how GENAH was applied to the study on the vibration of two concentric submerged cylindrical shells coupled by the entrained fluid.
The acoustic field in ocean with the sound velocity profile in depth was evaluated by Shell function method. Taking account of the vibrating area of the practical source, Shell function method can be applied to solving the acoustic field in ar-bitray inhomogenous media, including the focusing regions, without any kind of corrections. The computational result of the sound pressure was described by color to represent the propagation of the acoustic wave in the sound channel. Special attention of Shell function method is given to the acoustic waves received at the observation point, the travel time of rays from the observation point to the source, and the concerning area element of the source. In term of these information, the sound pressure and the propagational behavior can be predicted. Consequently, the travel time and the convergent state of rays arriving at the source surface, are investigated in detail to get an understanding of the effect of the area (or length) of the practical source on the sound field.
A new method (Ultrasonic Computed Velocimetry) to measure complete vector components of flow velocity is proposed. Using this method, it is possible to measure both of the flow velocity components along and transverse to the beam axis. This method is able to simultaneously measure the signs andmagnitude of the flow velocity components. Reflected ultrasound waves are used togetherwith fully linear signal processing procedures. The first step of the method is Fourier transformation of the received signals in the direction of the transducer array. The second step is also a Fourier transformation but in the polar axis directions. These two steps provide the two velocity compoments along and transverse to the beam axis. Detailed procedure and result of numerical simulation are presented.
An underwater imaging system was constructed. The confirmed performance are followed, the resolving power is less than 30mm for radial and less than 0.6 degree for azimuth, the target, which has 50*50mm squerecross section, was detected at 170m, and the reconstracted image was displayed in one second for the target setting at 20m.
Three kinds of experiments are conducted to determine the mechanics of flow inside two intersecting square ducts : flow visualization by means of dye injection, velocity measurement using laser Doppler anemometry, and pressure measurement using a piezometer. The geometrical dividing line in the intersection zone of the two ducts forms a flow divider separating the flow network into two independent, symmetrical flow units. The flow characteristics on the flow divider and in the intersecting section are disclosed.
Experiments are performed to investigate flow characteristics in intersecting ducys by means of particle-suspension flow visualization, laser Doppler velocimetry, and piezometry. The intersecting angle and the Reynolds number are varied. The flow characteristics on the flow divider and in the intersecting zone are disclosed. Other important disclosures include the occurrence of ramming phenomena in the intersecting section, and the existence of an "energy supply point"(with maximum velocity and minimum pressure) on the flow divider.
As a self-rectifying turbine for wave energy conversion, the new versions of impulse-turbine with self-pitch-controlled tandem guide vane are proposed. These include (1) variable-pitch flat-plate type and (2) variable-pitch splitter type. In order to examine the unsteady characteristics of the turbines, the experimental investigations have been made by a special turbine equipment and flow visualization using smoke wire method. The result shows that a high-efficiency impulse turbine can be developed through the use of the splitter. It is found that, in this case, the upstream guide vanes act as a slotted nozzle blade row and the downstream vanes as a tandem diffuser blade row by changing the pitch angle of the splitter automatically in a reciprocating flow
A system was developed to visualize the internal flow in the open impeller of a volute pump by photographing with slit lighting of stroboflash. The flow was visualized by the added tracer particles of polystyrene beads having mean diameter of 1mm. With this, velocity distribution relative to the impeller and secondary flow between the impeller blades can be observed by use of still camera mounted on the disc which rotates synchronizing with the impeller. And color slit lighting of strobof lash brought a 3-dimentional visualization of the internal flow by the aid of an image-processing method in emphasizing the intensity of color of each trace on the original picture.
Surface buoyant jets discharged on the sloping bottom was studied experimentally. Flow visualization techniques were used to reveal the behaivior of the interactions between surface buoyant jet and bottom slope. The configurations of density interface of the cross section on the jet axis were classified into five types and classification diagram was proposed. The deformation of the buoyant surface jet in the horizontal cross section due to bottom slope was also visualized. Periodic thermal fronts due to bottom slope which have been observed in the fields were reproduced in the experiments.
The fluid motion past a semicircular cylindar is visualized by means of alminum dust method in the water tank of NDA. Many photograph of flow pattern around a semicircular obstacle are taken at Reynolds numbers ranging 0.7×103 to 5.7×103 The separation points and the stagnation points are analyzed at the various angle of attack.
The stability of the secondary flow induced by a vertical circular cylinder performing transverse oscillations in a linearly stratified fluid at rest is investigated by means of flow visualization techniques. Compared with homogeneous fluids, the density gradient inhibits the onset of the three-dimensional instability. The instability appears as regularly spaced streaked flows along the cylinder axis and each streaked flow follows a wavy path in the horizontal plane in a certain range of amplitude and frequency of the oscillations.
The three-dimensionality of the wake of a two-dimensional circular cylinder is investigated by flow visualization experiments at low Reynolds numbers (Re-100). The experiment Ls conducted in a towing water tank with the aid of white dye as a tracer for visualization. The results are rather dependent on the initial status of the fluid, from which the cylinder starts to be towed in the tank. However, the three-dimensionality is always more or less discernible at low Reynolds numbers where the wake vortices seem to remain laminar until the decay at downstream. And this is still the case in the middle part of the cylinder span where the so-called end effects are considered as negligible.
In the well-known rotating annulus experiments we applied liquid crystal techniques of visualization in order to study the three-dimensional structure of differentially heated rotating fluid. Then we developed an idea of injecting several types of liquid crystal with different temperature ranges simultaneously for observing the fluid having a wide temperature. We call it multiple liquid crystal techniques (MLCT). Furthermore we use an apparatus having double rotating disks, on the small one of which an annular tank is put and on the large one a video-camera is set. In this talk we show, (1) simultaneous observations of surface flow and vertical one in a meridional sheet, (2)simultaneous observations of upper and lower flows in baroclinic wave, and (3) to what extent MLCT is useful for the quantative measurement of temperature in the analysis of zonal velocities of the axially symmetric flow by the wind thermal equation.
Generally, the temperature change of the cholesteric liquid crystals causes a shift in molecular structure and, thus a different color at a constant observation angle. On top of it, when the microencapsulation process for stabilizing the cholesteric liquid crystal and converting it into an easily manipulable form is fulfilled, the micro-capsuilzed cholestric liquid crystals act as a three-dimensional diffraction grating for light of visible wavelengths and show similar behavior to the Bragg Scattering effects observed in crystalline solids. Since this Bragg-type scattering gives rise to the characteristic iridescent colors around the micro-capsulized cholesteric liquid crystal, their spatial spectral color distribution around it needs to be known for applying it to the temperature measurements. This study focuses on the above optical characteristics of the micro-capsulized cholesteric liquid crystals.
The flow patterns around a circular cylinder placed on a flat plate are visualized by an oil-flow method and a china-cray method in high-subsonic flows; Mach numbers are 0.3, 0.4, 0.5 and 0.6. As well as the flow visualization, pressure distribution on the flat plate is measured. As the results of the flow visualization, it is clarified that a horseshoe vortex around the circular cylinder, which has already been observed in lowspeed flows and supersonic flows, is also observed in high-subsonic flows. The results of the pressure measurement indicate that the influence of the circular cylinder height on the flow field is greater than the influence of the Reynolds numbers.
An approximate skin friction estimation method by tracking oil dot movement under the effect of skin friction is proposed. The method uses the correlation between oil dot velocity and skin friction obtained by measurements for flat plate laminar boundary layer in a wind tunnel. The correlation is divided into two zones. Linear correlations at early stage of oil dot streak developments are observed. But, the correlation factors are much differ among oil dots. If oil dots streaks develop enough after a long period, the correlations converge into a certain band. Present method uses the later correlation to estimate skin friction values. Skin friction values on a very low aspect ratio rectangular wing having NACA 4412 wing section are estimated. The results show approximate skin friction values on bodies can be easily estimated by the present method.