In this paper, the dispersion process of coughed air in a stagnant indoor environment is visualized by the experiment using flour as tracer, and the transient CFD analysis coupled with concentration simulation. Moreover, the instant flow field in breathing zone immediately after coughing is visualized and measured by PIV. It shows that coughed air will be diffused into a considerable area even in a stagnant environment. The analytical results also indicate that the dispersion process and influence to another occupant of coughed air will be greatly affected by indoor ventilation situations.
CFD analysis are applied to the flowfield around a cubic building model placed in turbulent boundary layer. The results are compared with experimental data and flow visualization in order to clarify the effect of the velocity fluctuations on the prediction accuracy of time-averaged velocity fields around the building. Special attention is paid to the prediction accuracy for reproducing the flow behind the building. It is clarified that reproducing the priodic velocity fluctuation behind the building is very important for prediction of the distributions of velocity fields.
Currently indoor environment studies focus on phenomena around the hunun body at the microclimate level, and therefore the need for more realistic and detailed human body models has been pointed out. Numerical models representing closely the actual shape of the human body have already been proposed for seated female models (or androgynous models based on female body shapes), and are available for indoor environment analysis applications. However, other human body shapes have not been modeled. In addition, since existing models use coarse meshes, sufficient detailed data on various parts of the human body has not been gathered. This study aims to develop virtual manikins that represent human body scales for adult males and females as well as child (almost seven-year-olds). This report provides an overview of the development of models for seven-year-olds child.
Sloshing phenomena of liquid in a rectangular tank have been simulated by a CFD method, namely a large eddy simulation with standard Smagorinsky model. The free surface displacement was determined by solving the continuity equation for flow with unsteady moving boundary in the HSMAC iteration of determining the pressure and velocity. The calculated sloshing amplitudes are in good agreement with the experiment. The details of the sloshing phenomena, particularly the dynamic changes of the velocity and pressure distributions in the tank in forced oscillation could be studied effectively by a visual investigation.
We have investigated hydrogen explosion risk and its mitigation, focusing on compact hydrogen refueling stations in urban areas. In this study, numerical analyses were performed of hydrogen blast propagation and the structural behavior of barrier walls. The explosive source was a prismatic 5.27 m3 volume that contained 30% hydrogen and 70% air. A reinforced concrete wall, 2 m tall by 10 m wide and 0.15 m thick, was set 2 or 4 m away from the front surface of the source. Each of the tests measured overpressures on the surfaces of the wall and on the ground, displacements of the wall and strains of the rebar inside the wall. The simulated overpressures were in good agreement with test results for all three test cases. DIANA, a finite element analysis code was used for the structural simulations of the barrier wall. The overpressures obtained by the blast simulations were used as external forces. The analyses simulated the displacements well.
Field measurements using an image analysis technique, the large-scale particle image velocimetry (LSPIV), are conducted for a river reach having a series of groins in the Uji River. The measurements are performed using a digital video camera from a height of 27m of the nearby tower for meteorological survey. The river reach with a streamwise length of about 150m and the width of about 60m is cover by three-angle recordings. The measurement results from each angle are successfully connected with each other, by which the general flow feature of the region can be revealed with a reasonable accuracy. The measurement by an ADCP is also performed to obtain the internal three-dimensional flow structure. In addition, a numerical simulation based on the unstructured grid system of the shallow water equation is conducted to compare with the field measurement results and to evaluate the effect of the groins to the main flow.
Visualization of geographic information with GIS (Geophysical Information System) which manages the information with position coordinates is an effective tool also in regional environment study. In local environmental research, the approach from a macroscopic viewpoint which looks down at the whole field using GIS together with precise approach from the spot of the field study is required, in considering a long range and whole field environmental policy in a region. In this paper, the usefulness of visualization of the environmental information using GIS in regional environment study is verified by introducing the example of the approach from such a viewpoint in the Yodo-River Basin which Osaka University is carrying out. The example of rain outflow analysis, water quality analysis, forest book data analysis, and a forestry management plan is introduced.
In natural river flow conditions, vortices generated near the river bed occasionally reaches the water surface and detected as boil vortices. When viewed from an oblique angle we can find that such boil vortices generate surface ripples propagating in the outward direction moving with the surface flow, which can be used as tracer of surface flow measurements by imaging technique such as LSPIV. However, the characteristics of boil vortices are not fully understood so far mainly due to the difficulty in measuring surface flow fields. In this research, experiments using a laboratory flume are conducted to make clear the flow feature of the boil vortices generated by a single square rod. Measurements are performed using a high-vision camcorder and PIV with the erroneous vector correction algorithm proposed by the authors. It was made clear that boil vortices locally decelerate the surface flow. A method for measuring the boil vortex scale is also proposed.
The instability of the head shape of gravity current is investigated through CFD and EFD. The instability plays an important role in mixing stage. Three-dimensional instability of the head of gravity current is investigated by the experiments of the lock-exchange flow and by the computation using four different types of water tank. The flow visualization experiments are carried out with LIF technique to observe the three-dimension features of the head advancing along an channel. The numerical results show a good agreement with the experiments on the shape of gravity-current.
This paper shows the development and the application of the fast calculation method of view factors using computer graphics (CG) images. This method uses the perspective images made by CG technique in order to calculate view factors that are necessary in heat transfer problems. The process to illustrate the perspective images by CG corresponds to searching planes with numerical calculation method such as Monte Carlo method. We showed view factors could be calculated at high speed by using graphics hardware. It was found that the accuracy of this method using CG technique was within the acceptable limit. We applied PPM to the rolling mill factory model only to perform the thermal environment assessment. It was verified that this method has a possibility to become an effective tool for the analysis of heat transfer problems with heat radiation.
The development of a large vortex structure in fluid flow is responsible for some of the most fascinating aspects of fluid dynamics, such as mixing, transport, and instability. This paper describes an experimental study on the vortex nature of a pulsating jet issuing from a rectangular nozzle of an aspect ratio of 5 which has short parallel section upstream of the jet exit. The visualized images by hydrogen bubble method revealed the influence of the bounded plates upon the vortex nature.
The annular impinging jet is used to enable a uniform cooling over the wide range on the wall surface by the jet flow. The passage width was adjusted by changing the diameter of the inner pipe with fixing the diameter of the outer pipe. The lidded and lidless conditions of the inner pipe were also carried out. The pressure and heat characteristics on the impinging wall were examined under these conditions. As a result, it was found that the optimum conditions for a uniform cooling are about pipe diameter ratio di/do=0.7 and the lidless condition of the inner pipe. It was clarified by the flow visualization that the contraction flow which gathers to the center of pipe causes the loss of the effect of a uniform cooling.
Ceramic fibers that use as heat insulating materials for high-temperature furnace are produced in the process that a high-speed jet blows molten ceramic dropping from a furnace. The insulation performance is improved with longer length of the fibers and with lower content of spherical shots that solidifies without fiberization. These fiber properties are strongly affected by the shape of the jet nozzle though there does not exist the logical design method for it. Empirical methods are limited to optimize it. So that to detail information about the fiberization process is needed. In this study, visualization of the process using high shutter speed camera and schlieren method are attempted. The results from the high speed shutter camera show that fiberization process is completed before the fibers are blown downstream of the nozzle diameter. Visualization of schlieren method suggests existence of strong turbulence right downstream the nozzle which may affects the fiberization.
It is very important to clarify the structure and the behavior of the Coanda effect, which is one of the characteristics of the jet flow, from the viewpoint of the industrial applications such as a nozzle. In the former report, the structure of the Coanda effect was clarified by the experiment and its behavior was clarified by the numerical analysis. This paper clarifies the stabilization time and the adhesion situation of the jet flow by changing the offset ratio between the nozzle and the sidewall. And the shadowgraph similar to the experiment of visualization could be also obtained by the numerical analysis. Moreover this paper certified that the numerical analysis had the shock wave similar to the experiment of visualization.
With the steady increase in the number of cars, the exhaust sounds generated from the exhaust pipes of cars became a serious noise problem. Noise like this is called high frequency exhaust noise and shock waves are considered to play an essential role for the generation of the exhaust noise. Consequently it became necessary to reduce shock waves and to reduce the exhaust noise from the remaining shock waves by attaching a silencer to the exhaust pipes. Using the same calculation method, a numerical analysis of the propagation of shock waves was carried out using several different silencer models with internal structures of comparatively simple numerical analysis.
Plasmas are a typical example of functional fluids under the magnetic field. In the area of fluids engineering the behavior of plasma flow under the strong magnetic field is an attractive subject because of their characteristics of the high enthalpy flow and the luminosity. To realize the development of new plasma technology, it is important to study the effect of strong magnetic field on plasma jet. From this point of view, an experimental study was conducted to examine the effect of strong field induced by superconducting magnet on argon plasma jet. The jet images were taken by a digital camera through the viewing windows. The images of radial distribution of number density were also drawn by using the image processing based on the Abel-inversion. It is confirmed from the comparison with numerical results that these images are utilized for understanding the plasma jet characteristics.
A laser-induced phosphorescence phenomenon of vapor-phase biacetyl tracer is applied to ionic wind visualization for velocity measurements based on an image analysis. The phosphorescence phenomenon is used as a molecular tagging approach for gas-phase flow visualization due to the long lifetime of phosphorescence than fluorescence. The ionic wind is an electrohydrodynamically induced gas-phase flow phenomenon on corona discharges of a needle-plate electrode arrangement. This paper presents the experimental method and the typical visualization results of molecular tagging approach along with ionic wind, and a phosphorescence image analysis for velocity measurements is conducted.
The three-dimensional flow structure induced by normal shock wave/turbulent boundary-layer interaction in a transonic diffuser is investigated by a laser-induced fluorescence method. This diagnostic system uses an argon-ion laser as a light source, and the target gas is dry nitrogen with iodine seeded as a fluorescence material. The three-dimensional Mach number distributions are obtained by the system. Numerical flow simulation is also performed to check the reliability of the measurement and consider the flow field in detail. As a result, the numerical result represents good agreement with the measured flow field, and reveals that two vortices having the direction opposite to each other are generated in the vicinity of the rear leg of the bifurcated shock wave.
Understanding of hypersonic viscous interaction phenomenon over control surfaces is of particular impor-tance for designers of hypersonic vehicles. An experimental study of the behaviour of hypersonic flow past flaps is presented in this report. Impulsive glow discharge technique and Schlieren visualization using high speed video camera are applied to examining the structure upstream of the hinge. These experiments are conducted in a hypersonic gun tunnel at Mach number 10 and at Reynolds numbers based on the chord length ranging 0.8 - 2.12 × 105. The flap deflection angles studied are in the range from 0 to 0.523 rad at zero incidence. Numerical simulations based on the Navier-Stokes equations are also performed. Time lines obtained by the dis-charge technique are reasonable and the structure evaluated by the time lines correlates well with those through Schlieren and computational results. Normalized upstream influence increases with increasing Reynolds number and increasing flap angle in the range studied.
Cryogenic Inducer Test Facility (CITF) had been constructed at Kakuda Rocket Engine Research Center, JAXA. By utilizing this facility, it is expected that inducer performance in cryogenic fluid could be mor clarified. For experimental investigation of thermodynamic effect on cavitation, it is valuable to observe the cavitation in cryogenic flow, but the visualization is difficult. For this reason, we tried to estimate the cavity region in iquid nitrogen based on unsteady pressure distribution. By this method, the cavitating region against cavitation number was observed.The comparison between the experiments in liquid nitrogen and in cold water allowed us to estimate the amplitude of the thermodynamic effct. The liquid nitrogen experiments were conducted at two kinds of temoperatures to estimate the relationship between thermdynamic effect and liquid temperature.
Large eddy simulation was performed for a turbulent jet of diluted hydrogen. Treated were the case where hydrogen reacts with surrounded oxygen and the case where only mixing occurs without reaction. Coherent structures of turbulence in these cases were investigated. In reacting case, temperature rise causes significant drop of flow density, and, thus, velocity is two times as higher as the counterpart at the same position of non-reacting case. In spite of dramatic change in order of velocity magnitude, there is close similarity between two-point correlation of reacting case and that of non-reacting case. In two cases, coherent structure inclined against jet central axis was suggested through distribution of two point correlation and PDF of vorticity fluctuation vector.
In this paper, the simultaneous measurement technique of the temperature and velocity in a combustion flame was described using the digital-laser-speckle method and particle image velocimetry. This technique was applied to a Hydrogen diffusion flame diluted by Helium in an air environment and the structure of the flame was studied.
In this paper, the simultaneous measurement of three-dimensional flame shape and the velocity field by PIV was new lydeveloped to study the mechanism of fame oscillation of the diluted hydrogen diffusion flame in the air environment. This experimental technique relies on the flame visualization using the tracer particles of TiO2 generated from the reactive Mie scattering technique. It was found that the oscillation of the flame shape is axi-symmetrical and is consistent with the variations of velocity field in the flame.
This paper deals with the fluctuation in the lean burn of methane-air mixtures. We measure the fluctuation of brightness of premixed flames and obtain the power spectrum density of the brightness fluctuation. The power spectrum density has peaks, whose frequency corresponds to the oscillation frequency of premixed flames, and the 1/f spectrum appears in sufficiently low frequency range. Moreover, we perform the time series analysis on the brightness fluctuation. We obtain the attractor to investigate the characteristics of the fluctuation of premixed flames. The characteristics of fluctuation depend strongly on the equivalence ratio, and the results suggest that the fluctuation analysis is applicable to the diagnostics of flame behavior.
Isothermal gas simulation was performed for three patterns of carbon black (CB) reactors using standard k-ε model to treat turbulent flow. In addition, Lagrangean simulation was made to predict flow time corresponding to the time span of CB traveling in the hot gasses. Numerical results thus obtained are compared with geometrical properties of CB aggregate sampled from the CB reactors whose geometric shapes are the same as the numerical models. Numerical data suggested that flow time is key to control indicators of CB aggregate size.
Visualization of flame zone in turbulent premixed flames by utilizing acetone-OH simultaneous PLIF (Planar Laser-Induced Fluorescence) method has been demonstrated. Presently-proposed visualization concept is based on simultaneous imaging of "unburned zone" through acetone seeded in the fuel flow and "burned zone" through the combustion-generated OH radical by conventional PLIF system. Since only one laser and one detector combination is required, system cost is relatively low and user could avoid any difficulty related to synchronized control or superimposed imaging process. Instead, selection of band-pass filter plays important role on the current imaging procedure. From visualized images, multiple quantities related to local flame structure and status; such as 1) flame shape (including curvature), 2) localized relative OH mole fraction, 3) flame zone and so on, are successfully obtained. Applicability to further turbulent flame diagnostics is pointed.
Developing a reliable technique to measure two-dimensional temperature profiles of gas flows is significantly profitable for the development of advanced thermal devices, but is also one of the most challenging subjects. In an attempt to develop such a reliable and two-dimensional gas temperature measurement technique, we are developing the planer laser-induced fluorescence (PLIF) using fluorescences from two fluorescent materials. One of fluorescent material is used as a reference of laser intensity. The advantage of this technique is that it supposedly reduces the error due to the nonuniformity of laser intensity profile. As a first stage of this development, the temperature dependence of the fluorescence spectrum from ethylbenzene doped into N2 gas induced by the fourth harmonic (266nm) of Nd:YAG laser is investigated in the present paper.
Flame temperature is an effective indicator to estimate the amount of NOx formation. The Two-Color Method (TCM) is widely used to measure flame temperature of diesel combustion because the TCM can calculate temperature from color information of flame images. Taking flame images using the CMOS camera and analyzing those on TCM, however, have some problems such as the limitation calibrated range or measurement accuracy, by having digitalized all processes of the analysis. The purpose of this study is to evaluate the measurement accuracy of TCM analysis using CMOS camera.
Fluid-dynamical behavior of a jet exposed to sound waves is investigated by means of numerical simulation. Unsteady, three-dimensional, compressible Navier-Stokes equation including gravity term is solved with NSCBC (Navier-Stokes characteristic boundary condition). In order to simplify the computation by avoiding the calculation for chemical species, the jet of methane gas used in the experiments is replaced by a jet of hot air having the same density of the methane at the room temperature. The results of the calculation showed that the jet meanders negligibly at 110 dB in sound pressure level, although the experiments at the same level shows clear meandering structure followed by bifurcation. Notable meandering behavior appeared at 150 dB, impracticably high level. Shadowgraph images produced from the numerical results showed some analogous characteristics to those of the experiments.
Simultaneous measurements of CH and OH radicals by planar laser induced fluorescence have been conducted to clarify the relation between the flame structure and combustion noise characteristics in the swirl-stabilized combustor controlled by secondary fuel injection. The secondary fuel injection reduces spatial and temporal fluctuation of the high temperature region in the recirculation zone, which results in the reduction of the combustion noise. The frequency control of the secondary fuel injection also reduces the spatial and temporal fluctuation of the flame fronts in the flame zone (or flame bush). At the relevant control frequency, the flame bush becomes thinner and is confined to narrow region.
CH double-pulsed planar laser induced fluorescence (PLIF) measurements have been developed to investigate the dynamics of the flame elements in turbulent premixed flames. The time-resolved measurements of flame fronts were conducted in relatively high Reynolds number turbulent premixed flames stabilized in a swirl combustor. By selecting appropriate time interval of successive CH PLIF, movement of the flame front was captured clearly. In addition, by applying cross-correlation method for successive CH images obtained with minute time interval, displacement speed of the local flame element was measured.
In order to evaluate manoeuvrability of ships in its design phase, hydrodynamic forces and moment acting on the ships in manoeuvring motion must be estimated. Authors are working for developing a computer program using CFD (Computational Fluid Dynamics) technique for calculating hydrodynamic forces and flow filed around ships in manoeuvring motion. In order to develop reliable CFD codes, experimental data are needed for its validation. Authors having had so far reported such kinds of experimental data for bare hull condition carried out tank test for obtaining experimental data for conditions with a propeller and a rudder. Stern flow field of a tanker ship model is measured using an 8-hole Pitot probe which detects three dimensional velocity components. Effect of rudder angle and propeller revolution together with oblique angle and turning rate on flow field around the model ship in manoeuvring motion is clarified experimentally. Uncertainty analysis is also applied to the measured data and validity of the test data is examined.
The reduction of the frictional resistance can be possible by injecting micro bubbles along ship hull. So far, we have carried out many experiments of drag reduction due to micro-bubbles using a small high speed water channel and 50m-long flat bottom ship towed in 400m towing tank, and the drag reduction is surely obtained. Based on these experiments, we carried out a full-scale ship experiment of micro-bubbles as a promising drag reduction device. In the paper, we introduce the outline of the experiment and show the behaviors of injected micro-bubbles observed through totally 12 underwater cameras set around the ship.
A new method is proposed to reproduce transient small-scale oceanic eddy field. Four sets of 3-dimensional velocity information were obtained by using 4 Acoustic Doppler Velocimeters (ADVs) with simultaneous measurement. Each ADV was allocated so that it comes to the vertex of a tetrahedron, the edge length of which was 2.5-4m. Each time variation was decomposed into time and scale information by applying a wavelet transform. The spatial length and the moving direction of an eddy were estimated for corresponding time and scale from 3 sets of the wavelet cross-spectrum. Then, eddy field was reproduced as a time sequence in the physical cubic domain, the edge length of which was 80m. Finally, turbulence statistics, such as energy dissipation rate and diffusivity, was estimated from this reproduced oceanic eddy field. This reproduction method can be an effective tool for estimating the characteristic of the deep ocean turbulence.
Turbulent flow in a curved open channel has been investigated by PIV experiments. The curved channel model retains some geometrical features of a small curved river in Nara prefecture and is conceived for modeling the accumulation of contamination in canals or small-scale rivers. The PIV experiments are focused on the cross sectional flows in stream-wise and transverse directions which, respectively, give rise to primary and secondary vortex motions under the influence of the centrifugal force.
Remaining snow surrounded by a ground surface and a ground surface surrounded by remaining snow are called yukigata in Japan. Some of famous yukigatas have a name and oral literature. There are more than 300 famous yukigatas. The yukigatas have been used mainly as a kind of calendar for agriculture in most of the snowy regions in Japan since long ago. Recently, however, the yukigatas are being forgotten because the primitive ways for agriculture are disappearing with the progress of agricultural technology. On the other hand, the formation of yukigata is governed by the topography of the mountains and snow accumulation and snowmelt. Therefore, yukigatas have information on topographical features, distribution of mountain snow and climate change. Moreover, it is possible to use yukigata as sightseeing resources or material for nature education.
A very thin water veil like a transparent thin sheet of vinyl has been produced by shaping a double-disk nozzle in such a way to accelerate the water flow inside the nozzle. A double-disk nozzle that hangs from upper side was newly developed. Comparison of the simulated shape of the water veil with that of the experiment shows that they are almost identical. Human mind can be refreshed and relaxed by being inside of this water veil. In this paper, the application of water veil to healing of mind and body is examined. The analysis of the brain wave data using the emotion spectrum analysis method (ESAM) elicited that the water veil is very useful to recover freshness and effective in healing mind and body.
The blood flow in the heart can be observed as a colored image with medical ultrasonic Doppler equipment. As for this image, the component of velocity of the direction of an ultrasonic beam of a blood flow is displayed in blue and red. The component of velocity in an observing plane can be guessed from this component of velocity. This result is displayed according to the purpose. Here, the direct presentation of the flow vector was compared with the streamline display which quantized the blood flow. The vortex of a flow was easier to be observed by a streamline display. It turned out that a vector display tends to grasp the character of a flux.
We have done some attempts to understand the mechanism of commutation spark generation in universal motor from the image aspect using a high-speed camera. We have also mentioned about the generation of single and plural number of sparks at one commutator segment and the voltage between brush and commutator segment. The commutation sparks of the motor are generated with a sliding contact between brush and commutator segment in the moment that the segment is separated from the brush. And the width of the brush is just 10mm, this time, we were able to clarify position of the brush which sparks are generated and the relation between positive brush and negative brush.
Water management is the critical issue for PEFC. In this study, the water production and transport in an operating PEFC has been experimentally investigated using optical single cell. The separator of this cell was replaced by the current collector which has gas channel, and this channel was observed through view port. From the results of the observation, it was found that the nuclei of water droplets were formed in the gas channel and grew into the larger droplets. And these droplets moved being pushed to the gas flow and then discharged from channel. It was also found that the distribution of current density corresponded to water distribution and that the humidity of anode gas had a large effect on cathode water distribution. Furthermore it was cleared that cell voltage fluctuation caused by discharge of water.
We have proposed the Eigen pattern method, which makes it possible to carry out the computer watching, diagnosis, discrimination, inspection etc. on fully automated security and inspecting systems. Since our Eigen pattern method is based on the color information of distinct target, then it is possible to cognize when confronting to the geometrically deformed target having the same color information. On the other side, our Eigen pattern method could not distinct the different targets having the same color information. To remove this difficulty, we propose here a geometrical Eigen pattern method based on the Fourier cosinusoidal transform. As a result, it is revealed that fairly good cognition rate can be obtained by this geometrical Eigen pattern method.
After Newton mechanics had been established, major effort of human innovation had been devoted to enforce the human physical power, such as hand, foot and fighting power by many physical tools and mechanical devices. After spreading use of digital computers, most of the human innovative efforts are now devoting to work out the artificial human brain or compensative tool of human brain works. In the present paper, one of the methodologies to carry out the line signal diagnosis is proposed based on the some assumptions in natural phenomena.
This paper discusses an imaging of eddy current testing (ECT) data for surface breaking evaluation. The multicoil ECT probe utilized in this paper consists of transmit-receive (TR) type sensors as array elements to obtain the information on crack directions and deep situation. Switching two direction scan modes gives two-dimensional vector mapping as ECT images. The ECT signals of the TR type sensor also give the information on crack directions from their variation displayed on the complex number plane. Extracting a complex number component of the signals makes it possible to visualize directions of proximate EDM notches.
In this paper, the character of the noise in a medical X-rays image is first analyzed for the purpose of applying to the amount image of low incidence X-rays. Reasonable dominant noise in a medical X-rays image domain is X-rays quantum noise. This X-rays quantum noise is the spatial and time statistical noise according to a Poisson distribution. Second, a poisson distribution degradation image model is examined and a Poisson distribution degradation picture is created. Then, the average filter of the conventional method, a median filter, and a winner filter are compared with Wavelet Shrinkage filter processing to the created Poisson distribution degradation image. When a PSNR value is compared, since the good result was obtained, the way of a Wavelet Shrinkage filter proposes the new method based on a nonlinear Wavelet Shrinkage filter. This technique has the feature that useful information, such as edge of a image, cannot be spoiled but quantum noise can be removed compared with the conventional method. Moreover, as for the proposal technique, it turned out that the PSNR value is improved from the conventional technique.
Single Hot-wire probe is used conveniently at the velocity measurement of flow field. It couldn't acquire three-dimensional velocity components. In the periodic flow field, by using technique of signal analysis, several discussions on the flow structures could be carried out. In this study, the periodic structures in a wake of Savonius rotor are investigated by technique of signal analysis. The profiles of the time-averaged velocity, the correlation coefficient and the phase-averaged velocity could be found and discussed.
The vibration of car mirror is caused by fluid-dynamic force that is dominated by the flow structures and the unsteady behavior of the vortex when a car travels at high speed. In this paper, the turbulent structure of the car mirror with grooves wake was experimentally investigated. The instantaneous velocity fields were measured using PIV technique at a Reynolds number of 6300. By examining instantaneous and mean streamlines, vorticity contours and Reynolds stresses, the wake structure of the car mirror with grooves was compared to the car mirror without grooves. It is found that the region of the reverse flow, the size of vortex and Reynolds stress were reduced by grooves.
Pseudocolor image processing and characteristic pattern method were applied to PIV system for improving PIV accuracy in this paper. Characteristic pattern of the PIV images is extracted and is used as image cognition. However, this method generated false velocity vectors due to analogy of characteristic pattern of PIV images. As a new method, it is proposed to calculate the velocity vectors from the correlation of characteristic pattern of pseudocolor PIV images. It is found that pseudocolor image processing and characteristic pattern method are effective in PIV system.
In this study, the wavelet-based JPEG2000, the next generation image compression technique was applied to PIV for efficiently reducing the physical storage and the noise in images. For evaluating the relationship between image parameter and compression ratio, the PIV standard images and experimented PIV images were compressed by JPEG2000 and JPEG. It was found that the superior performance of JPEG2000 as compared to JPEG at any compression ratio. JPEG2000 method performs beyond compression ratios where JPEG breaks down, enabling compression of high-resolution PIV images.