In the well-known rotating annulus experiments we applied liquid crystal techniques of visualization in order to obtain clear video-pictures of internal flow and temperature in the 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. Furthermore we use a table 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. With these ideas clear video-pictures were possible to be taken throughout the entire region of the fluid. In this talk we show the video-pictures of the convections in the horizontal section near the bottom and in the meridional section of the fluid.
Liquid crystal suspension was used for the visualization of the temperature and flow fields. Almost all of this method have been applied to the natural convection fields. In the present experiments, a rectangular block is placed on the bottom-wall of a closed channel. The block is to simulate the Integrated-Circuit cooled by forced convection. The fluid was circulated by a pump. The temperature and flow fields of forced convection cooling arround the rectangular block were successfully visualized by the liquid crystal suspension of silicon oil.
A quantitative thermal flow visualization using thermo-sensive liquid crystals has been very popular to analyze heat transfer phenomena. In this method, a color-to-temperature calibration line is needed to obtain the temperature distribution. However, it is difficult to obtain the exact caliblation line because of its strong non-linear characteristic. In this study, a new algorithm for the calibration of color to temperature using a neural network is presented to improve the temperature measurement range.
Transient natural convection along a vertical flat plate was investigated experimentally. To find out the fundamental characteristic of the transient region, wall temperature patterns on the heated wall were visualized using liquid crystal sheet and were analized by image processing. It is revealed from the visualization that the horseshoe-shaped low temperature pattern generated by the streamwise vortex appears on the wall and that it plays a significant role in heat transfer. The spanwise length and the life time of the horseshoe-shaped pattern can be estimated using buoyant parameters, such as (κν2/g β qw) 0.25 and (κ /g β qw) 0.5, which are the characteristic length scale and the characteristic time scale in transient natural convection.
A method for visualizing qualitative temperature distributions around hypersonic vehicles is suggested. As an example of this method, a temperature layer over a slightly blunted wedge is visualized. The photograph indicates that there exists a radiation contrast along the wedge surface. From this, it is considered that the present method may be useful for visualizing gas temperature distributions around hypersonic models.
A qualitative theory of the first electric discharge method for visualizing shock shapes was established by considering the relation among the radiation intensity from the electric discharge, excitation function vs. electron energies, and gas molecular number density. By establishing the theory, it was found there exists the most suitable experimental condition for visualizing shock shapes. A three dimensional shock shape around a delta wing with a body in a hypersonic flow has been visualized successfully by utilizing the knowledge.
This paper treats the newly developed 3-dimensional display device, which incorporates a moving panel mounted with lightemitting diodes (LEDs). The display utilizes “afterimage phenomenon” to create 3-dimensional images in real space that surpass those offered by the CRTs used in current computer graphics. The display can beapplied to the shape design, the scientific visualization, and the visualization of medical data.
Considering about the condition of two contactingbodies under tangential force, local and micro slip (tangential displacement) initiates and develops before the macroscopic slip occurs. In this phenomenon, there would be various complicated contact conditions which can not be analyzed theoretically before. In some fields to control the tangential displacement, it is important problem to clarify the mechanism. In this paper, in order to clarify the mechanism of the tangential displacement, we try to make the micro-slip at the contact interface between rubber and glassplate visualize using the correlation methods.
We have proposed a new experimental method of generating Mach reflection phenomena in solids. The method is based on the refraction of a plane shock wave by a shaped material interface. The plane shock wave is generated in a target assembly by a flat plate impact of a highspeed projectile driven by a high-pressure gas gun. The shock collision phenomena have been studied by observing the sudden drop in the reflectivity of a mirror placed on a target material free surface. A compact high-speed streak camera system has been used for this purpose. We have made several experiments, and found that the present method is effective in observing the shock collision phenomena.
A new Image Tracing Velocimetry has been developed which uses the standing air bubbles in the circulating water channel as tracers. In this method, small air bubbles are illuminated with laser light sheet whose intensity is varying like saw-teeth wave to mark several sets of time history on a path line. The intensity profile, obtained by this method, is used to estimate the velocity. A feasibility application is made by measuring the uniform flow. Relatively high speed flows (over 1.0m/sec) can be measured by this method.
Using correlation technique concerning with binary digital tracer images measurements of electrically operated flow fields in insulating oil have been perfomed. The insulating oil, which is polydimethylsiloxane silicon oil of 50 cSt viscosity, starts flowing soon as it is subjected to strong electric fields generated by dc high-voltage. The electrode arrangement used for the measurements of fluid flow is a pair of rod - plane electrode system in which the rod becomes a high-voltage electrode. Experimental results of the measurements show that the fluid flow near the high-voltage electrode accelerates with dependent on an electrostatic force as the applied voltage is increased. The fluid flow also has the electrical effect that the velocity of fluid flow near the high-voltage electrode at negative polarity is larger than that of positive polarity. In addition, the rising phenomenon of fluid along the electrode appears at only positive polarity. Finally, it is concluded from the experimental results that the fluid flow originates in a dynamical influence based on the repulsive electrostatic force which electrically operates on the space charges of same sign as the high-voltage electrode polarity.
When applying correlation techniques to visualized images erroneous velocity vectors are often obtained. In this paper, new methods for detecting erroneous velocity vectors by checking the local continuity of flow are proposed. Differently defined several divergences of a flow are utilized for the detection. A re-correction method of the corrected velocity vectors is also presented. The SOLA algorithm (numerical solution algorithm for transient fluid flow) is used for the image processed data. The applied results of these methods to a confluence flow are indicated.
Combination of cross correlation method and stereoscopic colour photographs are appliied to obtain 3-dimensional velocity components. Measuring plane is perpendicular to the uniform flow direction and the plane is lighted by slightly thicker red and green slit light sheet, one of which has a short time lag Δt against the other. The colour photographs are seperated by 3-colour image processing device for the data of cross corelation method. Two kind of flow fields are measured and reasonable results were obtained.
An image processing technique based on particle-tracking has been developed to obtain instantaneously two components of velocity on many of the sections in three-dimensional space. The tracer particles in a semicylinder tank were visualized on several horizontal sections by means of parallel laser-light sheets generated from a scanning laser beam. The movements of the particles were recorded by a high-speed video system synchronized with the scanning. Since the obtained vectors were interpolated at the grid points on boundary-fitted coordinates (BFC), the derivation of vorticities were conveniently carried out in the transformed field of the BFC. As a result, the two-dimensional aspects of the complicated flow were captured over three-dimensional space.
In this paper, the effect of rear body shape on the wake structure behind vehicle and on its aerodynamic characteristics is clarified. Three different rear body shapes, with the same front and center body shape, are used. The flow behavior in the wake is observed by flow visualization using Digital Image Processing and numerical results. The authors obtained results that the aerodynamic characteristics of vehicles strongly depend on the behavior of the wake.
Perspective view of vortex structure in a fully developed region of a circular jet is reconstructed by applying a digital image processing to cross sectional pictures visualized using laser-induced fluorescence. The time of motion pictures is converted to longitudinal position by Galilean transformation of which constant is a convective velocity of the structure. A fast image stacking system using a personal compuer and a video image memory board is developed, and the resultant three-dimensional pictures are examined by stereoscopic display using liquid crystal shutter glasses.
It is very difficult to choose a image processing method for obtaining a suitable image according to the image measurement techniques, such as the socalled correaltion method, the FFT method, the tracer tracking method and so on. The neural network system has tried to use for selection of the image proccessing method for the tracer image correlation analysis. The developed system is very effective even with few parameters of the image data.
A pair of aerial photographs of the flood flow in the Agano River on Sept. 25, 1966 was analyzed by the cross-correlation technique to obtain velocity vectors over the area of 1700 × 1000 m of the water surface. About 340 × 400 velocity vectors were obtained at every 5.0 m in streamwise and 2.5 m in spanwise direction. The interval and arrangement of the longitudinal low-speed band and high-speed band appearing alternately in the spanwise direction over the water surface were analyzed and two kinds of spanwise scales of large scale turbulence were found; one is about twice water depth and another is 4 5 times.
A measurement system based on the color image processing has been developed to obtain simultaneously both temperature and velocity distributions in thermal flow fields, The thermal fluid motion is visualized by thermo sensing liquid crystal tracers and fine nylon tracer particles injected into the fluid. By using the developed color image analysis program, the R, G, B values obtained from the thermo capsules are trnasformed into the temperature, and the velocity vectors are extracted by tracking of the each nylon particle, simultaneously, This technique can be applied to analyse the dynamics behaviour of unsteady thermal fluid flows.
Velocity distributions within a rotating type reactor were measured by a suspended tracer-particle method. In this paper, first of all, the outline of digital image processing technique of tracer particle motions within a rotating column was described, and then the applicability for this method was evaluated. Finally, some examples of measurement within a reactor were discussed. Flow images visualized with suspended tracer particles were once recorded on the video tape recorder. The procedure was conducted as follows; 1) particle identification between different images, 2) selection of particle velocity vectors, 3) determination of particle velocity and 4) interpolation of velocity vectors to grid point over the flow field. The results obtained were summarized as follows; (1) Sample data were processed to check the validity of this method by using a circular disk dotted dummy-particle. From the point of view of flow visualization method, experimental criteria for this method were made clear. (2) This method was applied to measure the velocity distribution within a rotating column type reactor. As the result, a reasonable velocity field was obtained.
A new method for measuring velocity field by tracking particles is proposed. Kalman's filtering theory and the Chi-square test are applied to the algorithm. By using Kalman's filtering theory, the particle information at the (t+1)-th step is estimated by particle information at the t-th step. The Chi-square test is applied to correlate a particle image in the t-th frame with the same one in the (t+1)-th frame.
Linear shear flows with constant velocity gradients are made through a duct by putting unequal-spacing parallel rods in it. The flow characteristics of the shear flows are measured and motion of shepherical particles is investigated in the duct. Effects of the velocity gradients of linear shear flows at a high Reynolds number on lift applied on a spherical particle are investigated by photographing trajectories of a sphere falling in upward shear flows and those of particles suspending in horizontal shear flows using a high speed video system. It is made clear that lift is applied on a sphere from the higher volocity side to the lower velocity side.
A two-channel LDV system is used to carry out the air flow measurements around passenger car models in a scale wind tunnel. A 2-watt argon-ion laser is used as the light source. The main optical unit and the probe head are connected by optical fiber cables. The probe head consists of a compact LDV probe, a beam expander and a focusing lens, which has a long focal length and can he traversed easily. A new type signal processor, incorporating a digital auto-correlation scheme, is employed to process the Doppler signals. Mean air flow velocities and turbulence intensities are calculated by a microcomputer. The flow measurements on the wake of car models were performed by this system. The results of the experiments show that reverse flow takes place just behind car bodies, and can clarify the difference in the flow field between the cases with and without a rear spoiler. It has been pointed out from the results that the present LDV system provides accurate flow measurements around passenger car models in scale wind tunnel tests.
Clarifying the generation mechanism of aerodynamic noise is essential in attempting to reduce noise deriving from turbomachinery and high velocity vehicles. For studying aerodynamic noise, an air flow with quiet noise is very useful. Under these bases, a “Quiet Flow Wind Tunnel”, with the measuring section eauipped in an anechoic chamber, was developed and installed in 1982. The maximum velocity of air flow from the nozzle, with a section of 400mm × 400mm, is 50m/s and the turbulent level is below 0.5%. The noise levels around the measuring section are below 48dB (A) at a velocity of 35m/s. Studyies utilizing this facility include among others : vortex sound from crossing two cylinders, flow-noise from finned-tube bank, noise from vanes for a flow leaning. These studies concluded that simultaneous measurment on both the fluid-dynamic and acoustic phenomena is enabled by this facility. Conventional type wind tunnels are incapable for such measurment. The Quiet Flow Wind Tunnel is proven capable of making quantitative estimations on the generation of flow-sounds. The results of studies obtained through it are being effectively used in developing low-noise machines and systems.
The 10cm × 10cm Magnetic Suspesion and Balance System at the National Aerospace Laboratory is described. This system has three characteristics in its coil configuration and the model position sensing system and the way of controlling the model position. The NAL's MSBS has the ability of controlling the 6 degree of freedom in motion of a model. A 60cm × 60cm MSBS was designed with the data obtained by the 10cm × 10cm MSBS.
The authors already developed three-dimensional particle tracking velocimetry (3D-PTV) based on a binary correlation method for high speed particle identification. The technique of the 3D-PTV is applied to the measurement of the flows of water and air bubbles in a cylindrical bath with a bottom blowing air bubbling jet. The performance of the stereo matching and reconstruction for threedimensional particle positions and the measurement accuracy of velocity vectors of water flow are discussed. Besides, the trajectories of air bubbles are investigated and discussed.
In this paper, a new efficient measuring method of the three-dimensional coordinates of distributed tracers is proposed. In general, a method of measuring the coordinates is one of the key processes in the three-dimensional particle tracking velocimetry (PTV). Because theaccuracy of the measurement influences not only the reliability of the measured velocities but also the efficiency in finding stereo-pairs and the performance in tracing motion of tracers. The performance of the present method is achieved by two algorithms for stereo-pair matching and accuracy improvement which are based on a conditional arrangement of cameras.
A mixing flow in a cylindrical vessel agitated by a bubbling jet is measured quantitatively applying particle tracking velocimetry by the binary cross correlation method. Analysing hundreds of video frames by the method, instantaneous velocity distributions, particles paths and velocity fluctuations are measured in a relatively short time. Although a two-dimensional measurement are used in the present experiments, results such as particles paths and instantaneous velocity distributions could be discussed considering threedimensional factors.
A 3-D PTV (three-dimensional particle tracking velocimeter) is constructed for the measurement of an air turbulent boundary layer with zero-pressure gradient at free stream velocity of 4 m/s. A unique illumination technique is developed by using three strobe lamps and a multi-channel signal retarder to obtain relevant particles images in air flows of relatively high velocities. Tracer particles used are plastic micro-balloons (Expancel, Japan Fillite co., Ltd.), whose average diameter is 501μtm and density is 36 kg/m3. Examination of particles' traceability verifies that they can follow periodic variation of fluid motions up to 100 Hz, and therefore that their traceability is good enough to resolve streamwise velocity fluctuations in the turbulent boundary layer measured presently. Turbulence statistics including mean velocities, turbulence intensities and the Reynolds stress are presented and compared with hot-wire measurement, previous LDV measurement and DNS data. The present results are in general agreement with those data, thus demonstrating validity and usefulness of the present technique for the measurement of air turbulent flows. However, near wall measurement encounters difficulty caused by adhesion of the particles to the wall.
To improve the accuracy of BWR safety evaluation, it is necessary to measure void distributions in high-pressure steam-water two-phase flow. For this purpose, the authors have developed a new technique using a high-speed rotating disc for X-ray beam scanning. Using the disc scanner, void distributions were measured across a pipe cross-section every 2.5 ms under various conditions. The device can visualize the transient flow pattern on a color CRT in real time. Using the measured flow pattern, a new flow-pattern map was made for high-pressure steam-water two-phase flow in a horizontal pipe. Results were compared with a flow pattern map used in the TRAC code. The measured flow patterns are about the same as those of the TRAC code. There seems to be little pressure effect on the flow pattern borders as pressure changes from.5 MPa to 7 MPa.
In the three dimensional Particle Image Velocimetry, three dimensional positions of the tracer particles are needed. In order to determine the three dimensional particle position, at least two images taken from different angles are used, because the obtained image is two dimensional. Therefore, the identification of the same particles in both images is needed. Using the VVH method, three dimensional particle identification could easily be done 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.
This report is on applications of our measurement system which can measure and display velocity/displacement vectors in real-time by processing the B/W video signal of the objective image. It uses a 2-dimensional cross-correlation technique of binary video data to determine vectors. The measuring rate is 1/60 sec for 16 templates (areas). The first one is on a measurement of a blood flow velocity which changes its value synchronizing with the heart beat. The recorded video image is captured by using a high-rate VCR (1000 [pictures/sec]) and a microscope (x40). The image is that of micro blood vessels located in mesentery of a rat. Then we introduce some data processing techniques depending on the measuring method. In Addition, we present a measurement of a micro scale movement of a plant. By using the laser speckle pattern, the system can measure micron-meter order displacement. Horizontal movement of a plant is presented.
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, and 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 new governing equation can be applied to the case of illumination intensity is not uniform in measurement area.
In the large-scale gas or steam turbine, the flow around the blade tip becomes transonic, and the shock waves are generated in the blade passage. These shock waves induce the boundary layer separation and the vibrations of blades, which degrade the efficiency. This unstable flow phenomenon is closely related to the secondary flow associated with the large change in flow direction in the blade passage. To measure the secondary flow, the nonintrusive diagnostic technique is desirable, and the laser-induced fluorescence (LIF) method offers one of the best tools for this purpose. To prove the validity of LIF method in determining the temperature and velocity of the transonic flow field, the transonic nozzle with rectangular cross-section was made. The temperature and velocity obtained by the LIF method were shown to agree very well with those calculated from the static pressure measurement.
In this paper, experimental results of visualization and velocity measurements of the buoyancy-driven exchange flows through the small opening are described. This type flow might be caused by a pipe rupture accident in a high temperature gas cooled reactor. After helium gas had been filled in the test cylinder, the cap covered the top of the opening was abruptly removed. Then an ascending helium current issuing from the opening and an entering air current into the test cylinder were occurred. The ascending flows seeded with fine particles were illuminated by sweeping beam scanned by a polygon mirror in vertical and horizontal planes. And multi-exposure specklegrams of the flows were recorded on the films. The velocity vector diagrams of the helium current were obtained from the specklegrams by means of Young's fringe method. Experimental results show that maximum velocity of helium current depends on the shapes of the opening with/without throat.
One of the advantages of the laser differential interferometry (LDI) using Wollaston prisms, the difference of the two detector signals will therefore be essentially free from vibrations and laser output variations. LDI can be made more sensitive to optical path change by 2 to 3 orders of magnitude than classical interferometry. On this paper, LDI has been applied to density measurements in a propagating pressure wave in a tube. Our LDI system was specially designed for a shock tunnel experiments. The sensitivity was high enough to record the density variations by an acoustic or pressure waves. The time dependent profiles give the detail information on the process of formation of the unsteady boundary layer behind a propagating compression wave.
The feature and mechanism of flame acceleration and transition to detonation are not fully understood. In particular, the occurrence of “explosions in explosion” in the transition processes is very important phenomena which is worth studying carefully. The present study aims to observe this phenomena and to elucidate the transition processes by using the high-speed Schlieren photography.
Holographic interferometry has been successfully applied quantitatively to visualize shock wave phenomena. This paper will demonstrate that this flow visualization technique is more effective in observing three-dimensional shock wave reflection over cones than other conventional flow visualization techniques. It is well documented that, in a two-dimensional shock wave reflection over a wedge, regular reflection or Mach reflection occurs according to the shock Mach number and the wedge angle. When a shock wave reflects at the surface of a cone which has an attack angle, these two reflections can both appear simultaneously because of the difference of incidence angle. Depending on the attack angle of the cone, either regular or Mach reflection occurs. However, very little is known of the three-dimensional shock transition from regular to Mach reflection or vise versa. From a physical point of view, it is important to determine the transitional angle between regular and Mach reflection by using a holographic method. In this paper, a shock wave reflected from a cone at an angle of attack was visualized quantitatively by using double exposure holographic interferometry and diffuse holographic interferometry.
Experimental and numerical results of oblique reflections from ramp surfaces are shown for weak shock waves in carbon dioxide. The results are shown for several combinations of the shock Mach number Ms and the ramp angle θ. Density contour fringes is photographed by using a Mach-Zehnder Interferometer. Numerical simulation is carried out by using the MacCormack-FCT combined method. There is good agreement between experimental results and numerical ones.
Two-dimensional structures of radiation emission behind strong shock waves in air are observed by using an image converter camera, and the photos are processed by an image processor. Strong shock waves are generated by a free-piston, double diaphragm shock tube. The shock speed are measured to be from 9 km/s to 11 km/s for the initial pressure of 13.3 Pa. It is shown that the double-peak characteristic becomes increasingly clear as the shock speed increases over 10 km/s. This can be mainly attributed to the increase of continuum radiation from free-free and free-bound transitions of electrons.
The internal structure of a pseudo-shock wave in a straight square duct was visualized using color shlieren pictures and laser holographic interferograms, and the density distributions in the pseudo-shock wave were clarified. Next, the velocity distributions in the pseudo-shock wave were measured using 2-dimensional LDV, and the effect of wall boundary layers on the structure of pseudo-shock wave was clarified.
Finite difference schemes that use adaptive mesh refinement are studied to solve an unsteady shock diffraction problem. The results show that this algorithm is successful in capturing high resolutional solutions with shorter processing time than the corresponding uniform grid calculation.
New detection methods had been developed to detect internal and external flaws by means of the infrared radiometer. In previous studies done by the authors, various heating methods were available to improve the detection limit of the flaws. The paper shows test results of detecting flaws, such as surface crack, blow-hole, inclusion and separation. Passive and active detection methods were used to find the flaws by means of heater, sun, hot gas and lamp injection, environment temperature change and so on. This paper shows characteristics of detection limit and these related parameters by means of those methods.
There are many slope failures of roods in Japan. It takes much time and labor to inspect slopes. Concerning this investigation, We acquired that it is possible to search for caving and weathering from surface temperature information using a thermal video system of remote sensing. For this investigatino two kinds of experiment were carried out. From the results, in this unusual areas, it was shown that there was detachment, caving and fissure water; here also the thickness of the mortar was within 10cm.
Surface temperature of a automobile tire rises by heat generated with the repetition of deformation and deflection of the tire, and with the heat generated by friction at the tire contact surface ground. Non-contact measurement of tire surface temperature distribution with infrared rays is beneficial to such fundamental study of tire characteristics as endurance, rolling resistance and wear. Furthermore, the data can also be used for improvement research in tire design factor such as tire profile. Relations among tire surface temperature distribution and tire characteristics are explained with some examples.
When performing image measurement by infrared rays, a wavelength range of 3 to 5 μm or 8 to 13 μm is normally used to avoid atmospheric absorption due to remote measurement. In case of outdoor measurement of buildings, however, there appear effects of insolation and sky reflection. This time, we made and evaluated a prototype of an infrared camera with the range of 6.5 to 8.6 μm, and confirmed that the effects of insolation and sky reflection could be reduced. It was also confirmed that correction was possible by obtaining the temperature and humidity of outside air and the measuring distance, although there is an effect of absorption by water vapor in this range.
The three-dimensional particle tracking velocimeter (3-D PTV) is a powerful measurement technique which provides information on all three components of instantaneous velocity in a large space. However, there still remain several problems in the 3-D PTV; in particular, its application to air flow measurement is an urgent requirement in practical use. In this study, the 3-D PTV was applied to the measurement of a turbulent air flow in a duct of square cross-section. As a result, detailed distributions of the mean and fluctuating velocities were measured.
The vortex wake of a two-dimensional oscillating airfoil is investigated experimentally by the use of computer aided flow visualization and measurement techniques. The model airfoil of a NACA 0012 cross-section is set at a large incidence in excess of the critical angle of attack and subjected to a harmonic oscillation in pitch around the one-third chord axis. Some measurement is attempted to estimate instantaneous distribution of velocity and vorticity and the relevant evaluation is made as to circulation of wake vortices. On the basis of these results, the vortex wake characteristics in dependence on the reduced frequency is briefly discussed.
The flow visualization has been used successfully in experimental fluid dynamics. Recently visual demonstration of computational results is put to practice as a post processor of numerical analysis of fluid dynamics. In this study, the new technique is developed to display on a video monitor both the experimentally visualized flow pattern and animated results of computer simulation of the same flow at the same time.