The computer simulation on formation of methane hydrate of clathrate hydrate type I is carried out by molecular dynamics method. The simulated objective is a single cubic unit cell of hydrate type I containing 46 water and 8 methane molecules. The initial configuration is that 46 water molecules is randomly located in the cubic cell of length 12.0A. The MCY and LJ potential model is used for interaction between water molecules and between different molecules. After 26ps running time, methane hydrate is formed at 275K. The stereo computer animation for whole process of molecules' motion approaching to hydrate structure is obtained in conclusion.

View full abstract

Three dimensional structure of a rarefied gas jet impinging on a plate is studied experimentally. Pressure distribution on the plate is visualized by OPMS (Optical Pressure Measurement System) using pressure sensitive paint.
At the same time, shock wave system of the jet is visualized by LIF(Laser Induced Fluorescence). Combination of these two methods yields elucidation of interaction of the jet with a plate.

View full abstract

This paper proposes one of the methodologies to recovering a high-resolution image from a low-resolution image based on a database inverse approach. Arranging the flattened low-resolution image database in column-wise, it is possible to establish a system matrix. Flatting a low-resolution image data becomes an input vector, and also a solution vector whose order is equivalent to a number of data base images is assumed. The number of columns and rows of the system matrix are proportional to a number of pixels composing the low-resolution image and a number of database images. In most cases, a number of pixels are larger than those of database images, so that conventional least squares method is applied to this ill posed system of equations. As a result, a fairly good solution that recovers a high-resolution image, even if the noisy low-resolution image data are used for an input vector.

View full abstract

In recent years, rapid growth of high frequency techniques causes an electromagnetic compatibility (EMC) problem. Leakage magnetic fields out of the printed circuit boards (PCB) stimulate the miss operation and mutual action among the electronic devices.
This paper proposes an application of the 3-dimensional wavelets transform to the measured leakage magnetic field distributions along with a time. As a result, a simple example has demonstrated that the 3-dimensional wavelets approach exhibits its usefulness to identifying major dominant magnetic field source searching from the locally measured magnetic fields.

View full abstract

This paper proposes a vectorized signal visualization method based on a multi-resolution analysis of the discrete wavelets. We apply our approach to a signal processing of a differential type magnetic position sensor for the metallic objects. At first, to derive a frequency domain information, we apply a conventional FFT analysis to the sensor output signals. Second, we apply a wavelet transform to the sensor output signals. After expanding the sensor output signals into a multi-resolution form, we comprise a series of the signal vectors by combining the low level on and off loaded signals. As a result, we have succeeded in visualizing the no-load and target reaction output signals. Thus, it is revealed that our vectorization methodology based on the wavelet analysis may becomes one of the distinguished methodologies for a signal processing technique.

View full abstract

This paper proposes a methodology for visualizing the electromagnetic field distributions vicinity of the electronic devices. At first, we solve an inverse source problem in order to identify the magnetic field sources from the locally measured magnetic fields. Second, we calculate the magnetic field distributions from the estimated magnetic field sources. Finally, we extract the most dominant magnetic field distributions using the 3D wavelet transform.
In the present paper, basic principle and initial experiments to verify our approach are described. As a result, it is revealed that the magnetic field distributions near the electronic devices can be visualized from the locally measured magnetic fields. Further, we have succeeded in extracting the major magnetic field vectors as well as their sources by the multidimensional analysis of the wavelet transform.

View full abstract

Previously, we have proposed a current viewer in order to visualize the current distributions in the electronic circuits. We have succeeded in obtaining the good results for one-dimensional current distributions after de-convoluting the space transfer characteristics from the current viewer's output signals.
In the present paper, we try to visualize the two-dimensional current distributions in a printed circuit by combining the space characteristic de-convolution with the vector wavelets transforms.
At first, we independently measure the output signals when scanning the current viewer in the direction of x-and y-directions.
Second, we carry out the de-convolution operations to remove the space transfer characteristics from the output signals.
Third, we constitute the two-dimensional current vectors by combining the de-convoluted x-and y-directed signals.
Finally, we apply the vector wavelet transform to the noisy current vectors in order to extract the major current vector distributions.
As a result, it is revealed that a series of convolutions among the major current vectors extracted by the wavelet transforms employing different base functions visualizes the current vectors in the two-dimensional printed circuit without any threshold operations.

View full abstract

Surface information has been extracted by means of the Fourier -wavelets transforms. The method is composed of the three major steps, the first is to extract the global difference between the two faces by Fourier analysis. The second step is that wavelets transform is applied to the data obtained by the first step in order to extract the local difference. Finally, a set of multi-resolution results of the wavelet transform gives the Fourier-wavelets extracted results. Even if a limited number of cases, we have succeeded in obtaining the new information in addition to the conventional results.

View full abstract

Principal purpose of this paper is to extract a facial change among the faces at the different situations for the psychological applications. Because of the difficulties fixing the face location at a particular coordinate, an extraction of the facial change from the comfortable to uncomfortable is relatively difficult task for a computerized approach. To overcome this difficulty, we propose a method, which combines the Fourier with wavelets approaches. After, a global facial change is extracted by the Fourier transform; application of the multi-resolution analysis of wavelets makes it possible to extract the local facial changes.

View full abstract

Previously, we have proposed a new computer oriented methodology for a sentence structure analysis based on a linear space theory. Its result has clarified that any literatures are composed of the control led flow of the exciting and quiet sentences, sections and chapters. The flow mechanism of these sentences represents not only the identity but also feeling of the authors.
In the present paper, we apply our methodology to the Kenji MIYAZAWA's work focusing on the key words selection. As a result, it is revealed that the story "GINGATETUDOU NO YORU" is characterized by the actions of two boys and the word "2". In addition, It is pointed out that a small variation of the key words may become an important factor in the story.

View full abstract

Discrete wavelets have been applied to analyzing a R-R Interval tachogram. Consequently, a specific wavelet level indicates the dominant frequency that indicates driver's mental stress with the time process. This method is able to replace former Fourier base analysis in the driver's circumstances. The experiments are carried out with a driver carrying an electrocardiograph in a passenger car circulating a test course with 140km/h. The R-R Interval tachogram was obtained from the driver before and while driving. The motivation behind this work is to establish a driver's mental model while the driver operates a vehicle. The model contributes to safe and comfortable driver's circumstances.

View full abstract

In shallow water, sediment transport is caused under sheet flow. Particularly, net sediment transport in the offshore is caused by asymmetry of oscillatory flow under nonlinear waves. It is necessary to consider the suspended sediment to predict the net sediment transport during one wave period. In this study, the velocity of the suspended sediment is measured by the Particle Image Velocimetry(PIV) under asymmetric oscillatory flow in a tank. In addition, the concentration of the suspended sediment is estimated from the brightness. Then the temporal change of the rate of the suspended sediment transport is estimated by multiplying the concentrating by the velocity..

View full abstract

The heat transfer performance evaluation and flow field prediction in an automobile headlamp are very important from the view points of the heatproof ability, durability and ventilation performance improvements of the headlamp. In the present research, the heat transfer performance and flow field in an automobile headlamp model was investigated both experimentally and numerically. The Particle Image Velocimetry (PIV) was used to measure the velocity field of the heat transfer loop in the headlamp at first. Then, CFD simulation was conducted by using the PIV measurement results as the boundary condition of the CFD simulation.

View full abstract

The flow mixing performance in a heater unit for automobile has been studied by model experiment using the thermo-sensitive liquid crystal technique and the color tracer visualization technique. The former technique combined with the image processing provides a temperature distribution in the unit, while the latter shows the diffusion distribution of the main and heater flow. Both techniques provide useful tools for understanding the flow mixing performance of the main and heater flow in the unit. It is found that the diffusion distributions obtained from the color tracer technique reproduces the qualitative nature of the flow mixing obtained from the temperature distributions by liquid crystals. These visualization studies show that the flow mixing performance inside the heater unit depends strongly on the mixdoor angles. The mixing performance was also evaluated quantitatively by using the temperature distribution obtained from the liquid crystals downstream of the heater unit.

View full abstract

Studies are made on the visualization and image measurement of high-pressure diesel fuel sprays. The second harmonic of a double-pulsed Nd: YAG laser is used as a light source for exciting fluorescent dye, Rhodamine B (C28H31CIN2O3). The combined use of a high-definition CCD camera and a specially designed synchronization system has enabled well-resolved digital images of diesel fuel spray to be acquired with a thin laser sheet (0.3mm thickness). The development process of fuel spray is observed, and fuel spray tip distance and spray angle are measured as function of time after injection.

View full abstract

This paper presents the experimental results for the depth measurement of small particles using a depth-from-defocus technique. In this technique, the depth of each particle is estimated by evaluating the image blur of the particle from a pair of blurred images simultaneously taken with different camera settings. A pair of blurred images is captured in this study be means of an optical system with a single 3CCD color camera and two color filters. The small particles are illuminated by a stroboscope synchronized with the VD signal of the CCD camera to eliminate the blurring caused by the motion of the particles. Experiment is performed for the cubic cavity flow induced by a rotating disk that is the upper wall of the cubic cavity. The experimental results show the applicability of the present method to 3-D particle image velocimetry.

View full abstract

The effects of the jet velocity on the flow characteristics of the circular free jet added the annular suction flow were examined, provided that the velocity ratio of the suction velocity to the jet velocity is the same. The two-dimensional flow field was measured by PIV, and the pass frequency of vortices was analyzed by FFT analyzer using a hot wire. As a result, it was found that the time mean velocity and turbulent statistical values of the flow field in the vicinity of the exit of the pipe are approximately the same in all cases of the jet velocity. Therefore, it was clarified that the velocity ratio is one of parameter that dominates the diffusion phenomenon. It was found that the pass frequency of the vortices is observed clearly in the velocity ratio more than 0.84. As the Strouhal number shows almost a fixed value in all cases of the jet velocity, similarity of the unsteady flow was also confirmed.

View full abstract

Bubble curtain is expected to be a new type of oil fence because it can generate a strong and wide surface flow over the bubble generation system. However, the most suitable condition for the bubble generation system has not been investigated. In this work, the surface flow induced by the bubble curtain is measured by particle imagining velocimetry, and the parametric dependency on the gas flow rate, void fraction and bubble size have been made clear. Furthermore, the internal two-phase flow structure in the bubble curtain is discussed with the PIV measurement data.

View full abstract

In this paper, the structure and behavior of the supersonic jets issuing from dual parallel asymmetric nozzles, which had oblique outlets, were studied mainly by the flow visualization. The flow visualization of mean and instantaneous flows with time were conducted by the shadowgraph methods, moreover mean total pressure distributions were measured. It was clarified that effect of oblique nozzle outlet on structure of pseudo-shock wave, and effect of interference characteristics of dual oblique jets on distance of dual parallel asymmetric nozzles.

View full abstract

Some types of technique and system have been used in practical applications of Particle Image Velocimetry (PIV). PIV system composed with twin-YAG laser and a correlation camera is a typical one which can be applicable in the wide range of velocity. Its time resolution, normally, is limited at 15 Hz due to imaging technique. On the other hand, video PIV is useful for time series measurement of low speed flow, because of 60 Hz time resolution by using field images obtained by interlace scanning. In video PIV using interlace images, an interpolation technique is applied in order to obtain a full frame image, and it causes uncertainty and error of this method. In this report, an algorithm of video PIV without any interpolation is proposed and the results obtained are compared with ones by using interpolated images.

View full abstract

PTV( Particle Tracking Velocimetry) is applied to images with moving particle images. Properties required for image sensors to analyze movements of scattered particles are discussed. Much higher frame rate than 30 pps is essential, which is realized by parallel readout architecture. Lower descretization level and image compression effectively work to keep both high frame rate and high spatial resolution (number of pixels) for a given number of readout lines. 1) The optimum descretization level for PTV is 4 to 6 bit: 2) Image compression schemes generate weak false particle images, which can be compensated by post-processing if the scheme is not complicated.

View full abstract

The vortex flows in the wake of a circular cylinder were visualized by hydrogen bubble techniques. The images of the flow past a bubble-generating wire frozen by a flashing light were recorded by standard video cameras. A method of image processing for the automatic measurement of the temporal velocity profiles crossing the generating-wire was developed in the video-images of the flow. The successive data of the temporal velocity profiles were transformed into the data in space domain by use of Taylor-hypothesis, and the procedure to determine the velocity gradient tensor was established to investigate the kinematics structure of the vortices in the wake. In the image processing the lack of information due to the low spatial resolution of the video-images was improved by employing two video cameras and by analyzing the images with sub-pixel accuracy.

View full abstract

Simultaneous measurement of temperature and velocity in a three-dimensional flow field is carried out by using liquid crystal visualization combined with scanning light sheet technique. In order to obtain the temperature from the visualized color image, the spline fitting technique in a HSI color space is proposed for the color to temperature transformation and is applied to various points over the image plane to consider the viewing angle effect. The velocity distributions are analyzed from the intensity distributions of the two images illuminated by the two light sheets which are captured at the same position but with small time interval. This technique is applied to the study of thermal convection over a heated surface and the mechanism of thermal structures generated over the bottom boundaries are discussed.

View full abstract

A three-dimensional open-channel flow having a rectangular block on one side of the channel wall was measured by applying a conventional 2-D PTV technique to the vertical and horizontal images visualized by a laser-light sheet. A high-speed video camera with 200 fps was used to capture about 4500 consecutive images, from which the mean and the turbulent properties were extracted by applying the binary image cross-correlation method. The cross-sectional secondary flows were obtained by combining the 2-D velocity vectors in the vertical and the horizontal planes. It was made dear that the three-dimensional mean velocity field can be obtained with a reasonable accuracy by the presented PTV procedure.

View full abstract

Thermographic Phosphor (TP) is optical measurement technique for 2-D temperature distribution on solid surface, using the dependence of a luminescence intensity. This technique requires the pre-measurement of the luminescence on a condition of known and uniform temperature. We develop a new technique named "Composite Termographic Phosphor". This method uses composition of a few kinds of phosphors, which have different color and different dependence of intensity on temperature. This article shows the examples of this method. The time resolution is μs-ms order, higher than typical TP measurement.

View full abstract

There was no method for non-contact thermometry on a solid surface in liquid. IR radiation thermometry cannot be applied because of radiation from liquid surface. A new method for non-contact thermometry on the solid surface in liquid was proposed in this paper. Thermo-graphic phosphor method was arranged for this purpose.

View full abstract

A major advantage of the thermograph is that it allows noncontact temperature measurement to be carried out. It also has a disadvantage that to obtain its real temperature, the operator must first measure the emissivity of an object, and that thermographic measurement is intrinsically liable to be affected by environmental disturbances. To make effective use of a thermograph, it is important for the operator to learn those error factors. This article describes conceivable error factors to be taken into consideration and measures to take to minimize them.
If an appropriate observation wavelength range is selected after thoroughly studying the object to be observed and the measurement environment, temperature measurement with minimal error is attainable by reducing the influences of environmental disturbances as far as possible. This sort of approach also makes it possible to measure objects that cannot have been measured so far.

View full abstract

Formation and propagation process of local deformation slip-band in tensile experiments are visualized with dynamic digital speckle interferometry method. Interference speckle patterns on a deformation surface are taken successively with a constant speed. A whole deformation process of aluminum alloy (A2017) in tensile experiments is observed in real time by subtracting two interference speckle patterns sequentially with a constant time interval. As plastic deformation progresses, an inclined white band with constant width appears and propagates along the specimen surface repeatedly in an almost constant speed. As deformation increases, the propagating speed decreases gradually, until becomes zero when the specimen fractures finally at the position where the band stops. Transient process of the white band formation is captured with a high speed CCD camera. It is revealed that the white band is a sharp slip deforming region(Portevin-Le Chatelier band) consisted of concentrated inclined fringes. The moving picture encoding technique (MPEG) is introduced to analyze the huge volume of fringe pattern, and subtle changes of fringe patterns can be observed clearly.

View full abstract

The plane wave propagation in an aluminum block including a cylindrical solder, and that waves which is excited on solid/liquid interface by a line focused transducer are analyzed under plane strain state by the explicit finite element method. Those simulations are the first step to investigate nondestructive characterization with echo signals by various defects in materials. By calculating divergence and rotation of displacement field of the waves, the longitudinal waves and the transversal waves are visualized, individually.

View full abstract

Evaluation on CO2 LASER thermal shock damaged plasma sprayed coatings was carried out with ultrasonic immersion testing technique. The coatings were 3 types whose compositions were ceramics (ZrO2), ceramics to metal transition FGM(ZrO2 to NiCrAlY) and intermidiate(ZrO2:NiCrAlY=7:3). The damaged coatings were also observed using SEM(scanning electron microscope). Ultrasonic test images were compared with the observation by SEM. The results show that the number of cracks and the microstructure change were minimun on the FGM coating. And cracks, laminations and microstructure change of plasma sprayed coatings were proved to be detected easily with ultrasonic immersion technique.

View full abstract

Particle Image Velocimetry (PIV) offers many advantages for the study of fluid flows. The PIV has two processes, i.e., the image capture with visualization and the image analysis. In order to evaluate the image analysis system for the PIV, the Japanese PIV Standard Project (JPIV) proposed the standard images for PIV. In this study, the new PIV standard images are proposed for the three-components vector measurement in the two-dimensional cross section visualized by laser sheet. Using the images, the evaluation of the effectiveness and accuracy for the PIV system will be carried out. The developed PIV standard images are distributed using the Internet, (http://www.vsj.or.jp/piv/) and CD-R.

View full abstract

The standard images, provided by the particle image velocimetry standard project (JPIV) of the Visualization Society of Japan, are used to evaluate the velocity vector calculation based on a cross-correlation method. The effect of a sub-pixel calculation, a displacement length, an out-of-plane velocity, a number of particles and a particle size are discussed comparing with the correct velocity vectors. The evaluating method for the cross-correlation method and the problems are also discussed.

View full abstract

Particle Imaging Velocimetry (PIV) and Laser Doppler Velocimetry (LDV) measurements on the self-induced sloshing flow in a rectangular tank had been conducted in the present study. The PIV measurement result was compared with LDV measurement result quantitatively in order to evaluate the PIV system. The comparison parameters included the time average velocity, time average turbulence intensity, phase average velocity and phase average turbulence intensity. It was found that the PIV and LDV results agree with each other well in general for both the mean velocity and turbulence intensity, while there are some local disagreements for the turbulence intensity, which may be due to the different space resolution and the limited sample data of the PIV and LDV measurements.

View full abstract

This paper describes the results of PIV measurement of two-dimensional plane jet flow with self-induced sloshing, which are obtained by means of the so-called spatiotemporal derivative method. The research group for PIV measurement in Visualization Society in Japan has suggested this experiment for evaluating the performance of the analysis method. The results show the typical unsteady flow field owing to self-induced sloshing. PIV is a powerful tool for this experiment.

View full abstract

The self-induced sloshing is an oscillation phenomen on, which is excited by flow itself. In order to evaluate a self-induced sloshing, the flow with free surface in a rectangular tank having a horizontal plane jet was observed experimen tally. Under two separate conditions with respect to inlet velocity U0, the self-induced sloshing was found to be excited. The jet was observed to be oscillating only when the sloshing motion was excited. In this study, the jet fluctuation was measured using PIV under two separately excited conditions. The obtained unsteady velocity and vorticity distrib utions showed that the self-induced sloshing had different mode pattern s of the jet fluctuation, which was similar to simulated results. In order to clarify the sloshing growth, the distribution of oscillation energy supplied to s loshing motion was calculated from velocity distributions obtained using PIV, based on a feedback mechanism. The experimental energy distributions was observed to have different patterns under the different sloshing modes. Consequently, the validity of feedback mechanism was supported exp erimentally. It was experimentally clarified that the specific phase of jet fluctuation played an important role to sloshing growth.

View full abstract

Velocity vectors obtained by PTV contain usually mis-matched vectors. In order to estimate the whole flow field structure, the mis-matched vectors should be eliminated exactly. In the present report, a method of mis-matched vector elimination in PTV based on Laplace equation rearrange-ment is proposed. As a result, it is recognized that the present method has good performance by the verification after applying it to two-dimensional vortex flow and Karman vortex flow. Furthermore, it is confirmed to acquire higher performance by using a successive iteration type.

View full abstract

In the previous reports, the new image measurement technique using governing equation of fluid flow has been proposed. Numerical simulation and experiments have been made for the investigation of this technique. In this paper, the process of obtaining velocity distribution by.PIV (Particle Image Velocimetry) is discussed in the terms of the identification problem in dynamic system. It is found that the velocity is evaluated as a parameter of the model. This means that it is possible to obtain not only the velocity but also the pressure distribution. The proposed method is applied to the PIV standard image and cavity flow image. The results show that the present method is fairly effective.

View full abstract

We have developed the velocity gradient tensor method (VGT) which is a PTV algorithm. When the VGT method is used at particle points, we can simultaneously get both of the velocity vectors and velocity gradient tensor. It means that physical information can be directly extracted at particle points. The purpose of this study is to propose a new technique of the extraction of physical information at particle points from the velocity gradient tensor. The processing is applied to the vortex flow and PIV-Standard Image, the performance is examined from the precision for extraction of vorticity and stream function.

View full abstract

Conventional PIV method in which cross correlation coefficient is used has problem that erroneous vectors occur considerably if the correlation matrix is reduced to raise the space resolution. In tracer image, small turbulences are generally included in the average flow. In present algorithm, searching for image in correlation matrixes and dividing the matrix are alternated, and after that the second image transforms to approximate to the first image by using these value. Shift vectors at each point are obtained by repeating these operation until satisfying necessary space resolution. It is possible to search directly for a position where a correlation coefficient indicates the maximum value, because the shift distance is always smaller than the correlation matrix size. And decrease in computation time and prevention of erroneous vectors are expected from this method.

View full abstract

Anew Super-Resolution PIV algorithm has been proposed. The Super-Resohulion PIV consists of three component;
1) the standard coneiation PTV, 2) Particle mask conelation method for particle image extraction (KC method) and 3)Kal nan filter and Chi-sgiue test PIV algoritlun The present method is applied for simulation images to evaluate the perfomnance of the method. In a practical application, a flowin a Ruston turbine was measured by the present method

View full abstract

New algorithms have been implemented and tested for the use in particle tracking velocimetry (PTV). These new algorithms have been introduced mainly in the part of particle tracking itself, but as well as in the preceding part of individual particles extraction. For the particle tracking, the relaxation method is used with a number of improvement and refinement from the original algorithm. The extraction of individual particles or the detection of particle centers is a no less important process for the accuracy of PTV and there are four algorithms tested in the present work. Among them are included two new algorithms, using a modified Moravec operator for particle centers detection as well as a dynamic threshold method for image binarizaion.

View full abstract

In order to evaluate similarity between two particle distribution patterns in PTV, it is of importance to consider the pattern distortions during a short time interval. A method in this paper detects deformations of the particle patterns after estimating particle pairs between two sequential pictures. Shears and rotations in the flow can be determined by examining the estimated deformations, and erroneous particle pairs can be detected simultaneously. By repeatedly applying the screening process, both a number of obtained vectors and reliability can be increased. The processing time increases a little by adding the process, but it would be far less than an approach to determine the deformations first.

View full abstract

We proposed an extension of the processing of image cross correlation based PIV (Particle Image Velocimetry) using interconnected networks. The image cross correlation method is known as one of the most powerful algorithms for PIV using two image frames. However, when the size of interrogation window is too small, many erroneous velocity vectors appear in velocity vector distribution which is estimated using the image cross correlation. In this case, the correlation distribution is flat, because the average number of particles included in the interrogation window is small and patterns of these particles is simple and easy. But there are some peaks in the correlation distribution. There is the possibility that the correct vector is included into these peaks. In order to select a correct peak from the correlation distribution, the interconnected networks are introduced. The interconnected networks show high effectiveness with selecting the correct vector in correlation distribution with small interrogation size.

View full abstract

When the PIV measures flows, which include boundaries such as a solid wall or gas-liquid interface, measurements ought to contain erroneous vectors. Most PIV analysis algorithms are based on pattern matching technique. Although template patterns are expected to move simultaneously, the boundaries violate the precondition. The pattern matching using correlation technique has a good solution to the problem. This paper proposes a solution for the SSDA algorithm.

View full abstract

Large scale recirculating flow in a river was measured by a new image analysis method, Large Scale Particle Image Velocimetry (LSPIV), proposed by one of the authors. In this method, oblique-angled video images of river surface flow visualized by special tracer can be analyzed by PIV after the geometric image transformation. In this research, accuracy of the image correction was improved by introducing three-dimensional information of mark point coordinates.This method was applied to the surface flow between the five groins installed in the Nagara River in Japan. It was demonstrated that large-scale surface flow structure could be clearly visualized by the superposition of particle images.
In addition, the characteristics of the surface flow were made clear from the surface velocity distributions obtained by LSPIV.

View full abstract

An important quantity associated with the relative motion between a body and a fluid is force produced on the body. The two-dimensional flow past a circular cylinder is a very simple geometrical arrangement, and one about which there is a lot of information available. In this paper, the drag reduction phenomena on the flow past two cylinders were experimentally clarified. Experiments were carried out to visualized the flow past two circular cylinders arranged in a series by using dyestuffs or hydrogen bubbles in the range of the Re=60-80. It was shown that the wake of the first cylinder effects on the flow pattern of the second cylinder and the calculated results for the stream line agree well with the experimental results.

View full abstract

Based on a model for momentum transport and turbulence production near the wall by means of unsteady streamwise vortex, a turbulence control technique with longitudinal thin ribs were proposed for d-type rough wall boundary layer and an experiment with direct skin-friction measurement confirmed its efficiency for turbulent drag reduction. The maximum reduction rates of local skin friction coefficient compared with the original d-type rough wall flow and a smooth wall flows are about 10% and 3%, respectively. Examination of the turbulent intensity and Reynolds shear stress profiles shows that the vortex model assumed for the present control technique is reasonable. The streaky structure was observed near the wall and effect of the longitudinal thin ribs onthe probability density distribution of the spanwise spacing λz was investigated.

View full abstract

A simple control algorithm to determine wall deformation with wall variables is investigated based on physical arguments of turbulent coherent structure near the wall. It is found that the spanwise gradients of wall shear stresses are good indicators of a strong quasi-streamwise vortex associated with a meandering streak. The performance of the proposed feedback control through sensing the wall variables and using arrayed deformable actuators is examined by direct numerical simulation of turbulent channel flow. The mean friction drag is found to be reduced by about 10%. The conditional averaged spatio-temporal flow field is calculated to investigate phase relationship between the actuator and the quasi-streamwise vortex. The peak / trough of each actuator is connected downwards with the vortex. This suggests a possible control with sparser arrangement of sensors in the streamwise direction.

View full abstract

It is known that frictional drag in turbulent flow can be reduced considerably by adding a small amount of surfactant to the fluid. In order to investigate the mechanism of this phenomenon, the turbulent characteristics in surfactant aqueous solution flow in a planer two-dimensional channel has been investigated through visualization by dye injection, velocity measurements by LDV and time scale measurements through temperature fluctuation. Analysis of velocity fluctuation showed that Reynolds shear stress and turbulence production is diminished in drag reducing flow. Coherent structure was not obvious in this flow. It was observed that integral time scale become large near the wall. This finding suggests smaller dissipation and weakening of cascade process of turbulence energy. Lower turbulent diffusion can be explained by these characteristics found in drag reducing flow.

View full abstract

Turbulent channel flows for water and xanthan gum solution were investigated using a non-NTSC high resolution CCD camera. Over 2, 000 instantaneous vectors were obtained using PIV, and the detail of fluctuating velocity vector and Reynolds stress were revealed. 17.7% drag reducing flow of polymer solution shows widespread strong fluctuating region compared to that of water. The intensity of instantaneous fluctuating vectors is almost same for xanthan gum solution and water, while the time-averaged intensity of xanthan gum solution is lower then that of water.

View full abstract