While look down on an airport in the sky at night, we see a number of lights glittering, as if jewels were scattered. The lights in an airport play indispensable role for navigation safety. In this paper, an outline of lights of visual aids for air navigation (hereinafter reffered to as AGL; Aeronautical Ground Lights) is introduced by the following composition. At first, many sorts of lights used as AGL and their classification are shown. Secondly, the significance of AGL, even in the condition of progress of the technology of electronic aids for air navigation, is explained. Thirdly, the property peculiar to AGL, which is different from that of lights for other transport facilities, and the required performance derived from that property are explained. Finally, the future state of AGL and some examples of studies in recent years related to visualization are introduced.
Tornado is still not well understood and a mysterious natural phenomenon in spite of numerous past investigations. It has been extremely hard to visualize tornado and difficult to measure it by real-time scientific observation.
I am very interesting in long-and short-time scaled climatic changes of the East Asia since Last Glacial. Our presentation consist of reconstruction of Asian paleomonsoon changes by using non-glacial varves and loess-paleosd sequences. In particular, non-glacial varved sediments are effective as detectors of decadal to centennial changes of climate.
This paper describes an example of image analysis by dyadic wavelet transform. Wavelet modulus maxima on transformed plane gives the Lipschitz exponent expression, which is useful to examine the characteristics of singularity of signal or the edge of an image. It is possible to reconstruct the original image only using the few maxima points. It means that the conventional image analysis would be performed on the transformed plane with maxima points. The fractal analysis is tried as an example of the approach The visualized image of oil flow on a ship model is analyzed.
Characteristics of turbulent boundary layer with streamwise favorable pressure gradients were investigated experimentally using both the variable-interval time averaging (VITA) technique and the continuous wavelet transformation in which Gabor function was used for the analyzing wavelet. Especially, the research subject was focused on the bursting structure of the turbulent boundary layer. Results of experiments show that the Taylor's micro-time scale is the most suitable for the averaging period used in the VITA technique. Furthermore, cascade and counter cascade processes generated in the boundary layer were precisely visualized by the continuous wavelet analyses. The results show that the wavelet analysis can be one of the.most effective analyzing techniques for turbulent boundary layer investigation. On the other hand, non-dimensional bursting frequency was defined to detect the relaminarizing process of the boundary layer.
Activated-dust mobilization in a vacuum vessel of a fusion reactor under the Loss-of-Vacuum Accident (LOVA) condition was observed to investigate its flow characteristics from a viewpoint of the fusion safety research. The simulated dust was set on a floor in a small vacuum chamber and its flow mobilization when the LOVA occurred was visualized using a slit-light source, CCD camera and VCRs, and a moving speed of the mobilized dust was measured by a laser velocimetry. Experimental parameters in the present study are the breach positions on the vacuum chamber, set-up positions of the dust and temperature. The dust was conveyed from the vacuum chamber to the outside by a natural convection flow under a heated wall condition, and it was not go to the outside under a RT condition. The dust distributions in the vacuum chamber after the LOVA were clarified under conditions of different breach positions.
Surface tension induced (Marangoni-Benard) convection occurs at a surface of lithium bromide (LiBr) aqueous solution with addition of a small amount of surfactant was observed in order to investigate a mechanism of absorption enhancement by surfactant. Real time type laser holographic interferometry was used to visualize the transient phenomena occurred at/beneath the LiBr aqueous solution's surface in the very beginning(0-20msec) of steam absorption under vacuum condition(0.7kPa). Experiments were performed varying the initial surfactant concentration from 0 to 200ppm and the liquid layer thickness of 3-5mm. Pentagonal or hexagonal cell's patterns were observed at the surface clearly. And those cells evolved from small to large size instantly. Thereafter large scale chaotic eddies were induced at the surface.
Melting of ice in cylindrical capsules by natural and forced convections was studied by flow visualization technique. Surface temperatures were changed by the effect of natural convection in a cylindrical capsule with large diameter. In case of natural convection melting, the process was well simulated by axisymmetric heat conduction analysis when capsule diameters were small. In case of forced convection melting, surface temperatures were considerably scattered and the stagnation point showed the highest value. The shape of the solid liquid boundary became considerably asymmetric.
Low pressure axial flow fans without stator blades or guide vanes are generally used in order to achieve light weight, low cost and a simple structure, and to conserve space when mounted for automobile cooling system. However, since flow resistances in front and back of the fan are very strong, air tends to flow diagonally at the fan outlet side. The fan does not operate as an axial flow fan. In this report, we describe work conducted on a motor fan, mainly from the standpoint that analysis and improved understanding of actual air flow conditions lead to improved design. As for the measurement of air flow at the outlet and inlet side of the fan, the five hole-pitot tubes were used. And the reverse flow area was visualized to adhere tracer particles which are in the air flow to the pressure surface of the blades. As a result, we could predict the air flow among fan blades and portion and shape of the reverse flow area. These data were useful for designing the mixed flow fan which has the structure of an axial flow fan.
It is difficult to exhaust the polluted air and dust effectively, only by the ventilator or fan. Then, a compound swirl type exhaust device has been newly developed by the authors. The compound swirling jet consists of a circular free jett and the annular swirling jet mounted on the same axis by a double coaxial pipe. This system can constitute the gas range in the kitchen, smoking room and dusty factory. This system can achieve more effective ventilation than conventional system. In this study, the proposed system is visualized and analyzed by using PIV.
In Bénard-Marangoni convection, both buoyancy and surface tension effects are involved, and beyond the onset of convection, polygonal cells are observed. Visualization of the convective patterns have been carried out using two methods, namely interferometry to visualize the free surface deformation field, and infrared thermography to visualize the interfacial temperature field. Images of the convective patterns were recorded at regular time intervals. The images were digitized, and appropriate software allowed us to obtain the values of the relevant functions. The two techniques are complementary. The thermography allows visualization of the entire pattern, including peripheral cells, whereas these cells cannot be visualized, by interferometry, due to the fact that this technique cannot be used in the region with a meniscus. For very thin oil layers, only thermography can be used. On the other hand, interferometry is more sensitive to the interfacial fluctuations, and therefore is better for the study of temporal dynamics in the flow.
Fluorescent solution microcapsules (diameter < 100 μm) have been invented as tracer particles suitable for the long-term tracking of 3-D Lagrangian trajectories in the rotating annulus fluid experiments. In more than 10% of the tracking experiments, the microcapsule was observed to follow the flow passively for more than 10 hours, at their maximum 18 hours.
Field tests for air change rates in a test house were performed to develop a new method of measuring air change rates using a video imaging technique. Air change rates were measured from the decay curves of video image signals obtained by the step down method assuming perfect mixing of smoke particles inside the spaces. With the proposed video method by adjusting the pedestal level and f-stop of the video camera, it was possible to measure air change rates with virtually the same precision as derived from the decay curves of smoke particle concentrations using an aerosol monitor. As a new tracer, smoke liquid mists without dirty residuals were also tested and compared to the gas method using SF 6. It was verified that the video method using smoke liquid mists could also precisely measure air change rates with an error of less than 6% in comparison with the gas method.
Rapture of cerebral aneurysm is strongly associated with subarachnoid hemorrhage. The medical statistics indicate that cerebral aneurysm occurs predominantly in the arteries of branching with sharp curvature where flow and wall shear stress change abruptly. In this paper, the numerical simulation has been conducted to investigate effects of curvature on the flow pattern in the artery. The results have shown the periodic oscillations in the flow field, which is correlated with transient behavior of secondary flow and separation. The details of flow behavior such as effects of curvature were visualized using the commercial software FIELDVIEW.
This study is concerned with the large-eddy simulation (LES) of a turbulent flow in combustor with a complex geometry. In the paper, a jet is considered to discharge into a sudden expansion and to impinge on the circular plate located in the combustion chamber. Its flow pattern resembles that of a premixed jet-combustor. Thus, the purpose of this study is to investigate details of the flow phenomena in such a combustion device. In this calculation, we constructed the numerical code using combined grid technique based on the generalized coordinates and the cylindrical coordinates. This method can eliminate numerical difficulties related with both a singular point in the cylindrical coordinates and numerical errors in the generalized coordinates at the place where the mesh is severely distorted.the smagorinsky model was applied to the subgrid-scale stress. The Reynolds number was 5000, based on the bulk velocity and the diameter of the inlet section. The mean velocities are compared with experimental data in order to verify the accuracy of present analysis results.
In order to improve the measurement accuracy of the successive abandonment method, three sub-pixel analysis methods are examined about their precision and analysis time. Among them, the weighted average method has the lowest precision. And two others, a reflection point method and a shifted template method, have similar precision. Measurement precision is examined by rotating and shifting a solid pattern. As for analysis time, so far, the former method seems to be faster than the latter.
In Particle Image Velocimetry (PIV), the successive abandonment algorithm is known as one of the efficient technique, and it has been widely applied to velocity field analysis of fluid flows. In order to improve this technique as a high accurate technique for the wide dynamic range, the establishment of a sub-pixel processing is required. In this paper, a new calculation method in the successive abandonment algorithm is proposed as a technique of the sub-pixel processing in which the complemental error-function is used as the fitting function for the distribution of normalized accumulated-intensity-difference. The technique was applied to reconstruct velocity vector map of a synthetic PIV image. The results obtained show that the technique described here meets the requirement of fine sub-pixel processing of PIV image with only slight increase of the total processing time.
The brightness distribution cross correlation method which is used widely in PIV measurement for gray scale image takes a long CPU time to obtain the flow velocity due to searching the maximum correlation region. To the contrary, an effective PIV algorithm using spatio-temporal derivatives was proposed by Okuno et al. However it needs a flow field model to supplement the lack of information obtained by two consecutive images. In present paper, a new method using three spatio-temporal derivatives is proposed, in which three consecutive images are used to obtain pure measurement value with short CPU time. The performance of the method is examined by uniform flow, two-dimensional vortex flow and meteorological satellite image.
Pattern tracking algorithm using gray level difference as a similarity index of image fragments are inspected thronugh the application to the standard images which simulate images visualized with particles. It is shown that the performance of the algorithm decreases suddenly when the percentage of the particle area decreases to lower than 20%. The performance decreases also to the condition of high out-of-plane velocity, but the generation of incorrect vectors are suppressed in the successive abandonment prepared as a high-speed version of tracking algorithm, provided the percentage of particle area is high enough, due to the effect of statistical inspection involved in the algorithm. An idea to improve the quality of visualized images to prevent the decrease of tracking performance is also proposed.
Flow patterns of a surface tension driven convection (Marangoni convection) in a liquid bridge were measured using three-dimensional particle tracking velocimetry (3-D PTV) in a microgravity experiment conducted on the TR-IA#6 sounding rocket. The dimension of the liquid bridge was 28 mm in disk diameter and 20 mm in length, and the temperature difference of 50 K was imposed between the heated and the cooled disks, thus achieving a super critical condition. The flow patterns were observed through the transparent heated disk with three CCD cameras simultaneously, and their images were analyzed to perform particle tracking. Three-dimensional particle trajectories so obtained exhibited unsteady and complicated flow patterns showing vortex-like circulation zones in the corner regions near the disks.
National Space Development Agency of Japan (NASDA) successfully launched the Tropical Rainfall Measuring Mission (TRMM) observatory at 06:27 (JST) on Nov. 28, 1997. The TRMM satellite carries the first spaceborne Precipitation Radar (PR) which was developed by NASDA and Communications Research Laboratory. The PR can measure the horizontal and vertical structure of rain day and night, and over ocean and land. This capability allows scientists for the first time ever to grasp the three-dimensional structure of rain in the tropics and sub-tropics around the globe. In addition to the PR, the satellite carries four more sensors which were developed by National Astronautics and Space Administration (NASA): the TRMM microwave Imager (TMI), the Visible Infrared Scanner (VIRS), and the Cloud and the Earth's Radiant Energy System (CERES), the Lightning Imaging Sensor (LIS). Preliminary results and images from these sensors are shown.
Remote sensing data provides useful information for monitering and managing global environment, disaster and resources. In this paper, the problems of remote sensing data analysis are first analyzed and a new approach to the automatic terrain understanding, which we called "information fusion approach", is explained. Then a unified method to process spatial information as well as spectral information is briefly described with a few examples.
Some example of flow visualization of the sea by using the Advanced Earth Observing Stellite (ADEOS) "Midori" are presented. These include: (1) North-south flow pattern of the Kuroshio Extension, which was affected by slopes of the Japanese Trench, observed using Ocean Color and Temperture Scanner (ADEOS/OCTS), (2) Detailed structure of upwelling off Peru for non-El Nino event, observed using ADEOS/OCTS, (3) Flow visualization of the coastal current in the Isahaya Bay, Kyushu, before and after closing of the bay mouth, observed using Advanced Visible and Near-Infrared Radiometer (ADEOS/AVNIR), and (4) Flow visualization of longitudinal vortices formed in the wind-wave boundary layer, observed using ADEOS/AVNIR.
Abstract By processing JERS-1/SAR data with a technique called Interferometric SAR (INSAR), we succeeded in quantifying cruatal movement due to the NW Kagoshima Prefecture Earthquake (M6.3) of March 26, 1997. These outcomes agree with the crustal movement obtained from a field survey. It can be concluded that the observation data from JERS-1 SAR make it possible to quantitatively measure crustal movement due to earthquake.
There are few data on ocean current observation by ships and drifting buoys in the Sea of Okhotsk. This situation is the obstacle to improve the accuracy in the numerical prediction of sea ice in the Sea of Okhotsk. To investigate the features of the ocean current in this area, the satellite images are analyzed using Shannon entropy, which expresses the disorder of distribution of a parameter in the image, and allows the extraction of the patterns associated with eddy and current on the sea surface. Here, NOAA/AVHRR infrared image is used to calculate Shannon entropy in the Sea of Okhotsk, and its distribution is illustrated. By selecting the appropriate minimum area for calculation, ocean eddies and currents are clearly indicated in the distribution of Shannon entropy.
Monitoring of natural disasters by using the visualization technique of remotely sensed data is described. Oil spill detection in Japan Sea by RADARSAT SAR data which occurred in last January is mainly discussed. The pattern of oil spill could be detected as a dark area in the SAR image, since the radar back scattering from sea surface was suppressed due to the smoothing effect of spilled oil. It became clear that the detection of oil spill was difficult under the stormy weather condition such as winter season of Japan Sea, since the condition of oil spill detection was closely related to wind speed and wave height. In order to monitor natural disasters, it is important to observe disasters quickly and frequently. Visualization technique is also important to compute physical parameters from images.
Aircraft and ship are often used to observe sea ice condition. The observation by radar from shore stations is another effective method. Recently it was realized that the satellite remote sensing was very effective to obtain sea ice information. The satellite remote sensing is superior to other observation methods in its capability of wide range observations and in its regularity. There are several types of sensors and each has its advantages and shortcomings. This paper discusses their advantages and shortcomings and purpose how to use the data obtained by satellite remote sensing.
Flow-induced vibration of articulated column in wave-current coexisting fields has been investigated experimentally. The experiments were carried out on concerning the cylinder supported by spring where the reduced velocity varied from 1 to 5. This paper presents the measurement of the response of flow-induced vibration, observation of flow fields and lift force acting on cylinder in harmonic flow. The flow visualization of the water surface was made using the bead of firing styrene whose diameter is 2-3mm. It concludes from the experiment result concerning the articulated column in wave-current coexisting fields that it vibrates greatly in the right-angle direction of the flow with twice the period of incident wave.
Waving wing is a basic model for the analysis of fish-like propulsion in two-dimensional case which achieved high efficiency in comparison with the ordinary artificial propulsion system. The authors have developed a waving wing model, and consider the flow field around it in the previous report. The model motion is controlled through six parallel lines, and it achieves not only the sinusoidal but also any periodical motions. In the present paper, the flow field is visualized and measured in the case of non-sinusoidal motion that simulates the impulsive starting of fishes and the swimming motion of human legs.
The velocity field relative to the rotating blade of a Darrieus wind turbine has been measured by particle imaging velocimetry and the dynamic stall phenomenon of the wind turbine is studied in detail. Three stall vortices are generated in a cycle of rotation and they grow in size with an increase in the blade angle. The measured velocity field around the blade are well reproduced in the flow visualizations by dye injection technique.
We have been researched on the velocity field measurements of EHD flow. Thus paper describes PIV measurements of the EHD flow that is created by injection charge motion on free surface of dielectric liquid. Some experimental results show steady EHD flow with an interesting vortex for lugh resistivity dielectric liquid such as silicone oil. The velocity fields of the EHD flow are successfully obtained by means of the flow visualization technique and the PIV technique.
In this paper, authors have applied PTV and PIV techniques to measure behaviors of rising bubble and induced flow in a vertical cylindrical pipe. The bubbles rise in regular space from a bottom nozzle of the pipe filled with silicone oil. In the experimental conditions, Reynolds number is from 0.8 to 1.0 at the diameter ratio 0.25 of the bubble to the pipe. Bubbles are pictured from front and side directions by two CCD cameras. By analyzing individual pictures, shapes and dimensions are obtained. From the analysis of sequential pictures, velocities of the bubbles and the flow are measured. The data enable to estimate apparent drag coefficients of the rising bubbles.
The paper introduces a quantitative measurement technique for analyzing transient deformation of liquid-liquid interface through which a sphere penetrates. Water in room temperature was filled up to 170mm depth and a layer of silicon oil was put on the water with 30mm or 40 thickness. A 6.0 mm diameter acrylic or brass ball was set first at the upper surface of the oil and then released In order to record the transient phenomenon, a high-speed video camera was employed. The upper oil is dyed dark blue help extraction of the boundaries between the two liquids. The velocities of the falling ball were determined from coordinates of the center of gravity in the sequential pictures. Along with the velocity, the volume and the interfacial area of the oil is dragged into the water. And the authors are trying to measure the velocity distribution of the entrainment flow is obtained quantitatively using PTV technique.
A new PIV technique is proposed for the measurement of river flows. In this method, environment-friendly tracers made from corn starch, normally used as shock absorbers, were used for visualizing the surface flow Oblique-angled tracer images were taken from the river bank, which were then transformed to non-distorted images before the PIV analysis by using a mapping function. A new feature of the method is the introduction of threshold level that detects only the tracers; only those templates containing a portion of tracers were used in the PIV analysis. The application of the method to the flow between the groins in the Nagara River revealed the existence of complicated re-circulating flows.
Wall shear stress distributions of open-channel flows were measured making use of the binary image cross-correlation method (BICC), one of the PTV techniques. Flow fields close to the wall were visualized by a laser light sheet with small tracer particles and the particle images were recorded on a DV format tape using a digital video camera. The images were transferred to a personal computer as a movie file(an AVI file), divided into a series of bit map files(BMP files), and finally transformed to gray-scale binary data before the PTV analysis. Thousands of consecutive images were successfully captured by using this procedure. The shear stresses were estimated from the distributions of turbulence properties very close to the wall. Several estimation methods were compared and their accuracy was discussed in detail.
It has been pointed out that there exist coherent vortices near a free surface in rivers from field observations and that these structures have a close relationship with the "bursting phenomena" generated near the wall. The turbulent structure near the free surface greatly depends on the Froude number and the surface-wave fluctuations. Furthermore, it has been pointed out that the coherent structures and the turbulence statistics near the free surface are closely related with each other. In this study, PIV (Particle-Image Velocimetry) was used to measure evolutionary patterns of coherent vortices in the center of channel. The mean bursting period was evaluated then with a laser Doppler anemometer (LDA). In this way, a relationship between the "bursting phenomena" and the "boils (surface renewal eddies)" was investigated intensively as a function of the Froude number.
This paper describes the results of the flow visualization of cavity in open-channel flows by means of a Particle Image Velocimetry(PIV). The comparison of mean values, between the results of flow visualization and the high-accurate turbulence measurements conducted by making use of a two component fiber-optic laser Doppler anemometer (LDA) was carried out intensively, and the comparison of coherent structures, between the PIV results and the results of Large Eddy simulation(LES) was also conducted. The coherent structures were investigated in mixing layer by time-space correlation analysis. As the result, the characteristics and effects of coherent structures were revealed and then discussed.
Various anemometers, such as a pitot tube, hot-film anemometer and laser Doppler anemometer, have been used to measure the turbulent structures of closed duct flows, boundary layers, open-channel flows and so on. However, it is difficult to investigate of coherent structures such as surface vortices in open-channel flows. In this study, the turbulence measurements of open-channel flows with the vegetated zone at the half channel width were conducted by making use of a Particle Image Velocimetry(PIV). It was found that the horizontal vortices near the free surface are generated by the shear instability which increases with an increase of the vegetation density and also that the horizontal vortices were affected strongly by the vegetation density.
High-pressure diesel fuel sprays and their developing process after injection were observed using a novel visualization technique based on the laser-induced fluorescence (LIF). The fuel chosen was O-Solvent in which Rodamine B(C28H31CIN2) was dissolved as fluorescent dye at a mass concentration of 30ppm. A frequency-double Nd:YAG laser (532 nm wavelength and 7ns pulse width) was used to excite Rodamine B, which emits fluorescence of 590nm wavelength. A unique synchronization system was developed to control the timing of fuel injection, laser emission and image acquisition so as to capture spray images at an arbitrary stage of their developing process. It was demonstrated that not only the overall structures but also the deeply internal structures of the spray were clearly visualized with spatial resolution fine enough to image individual fuel droplet in the core of the spray.
When condensation occurs in a transonic flow fields, the flow is affected by the latent heat released. In the present study, a condensing flow was produced by an expansion of moist air in transonic flow fields using circular bump model and shock waves were occurred in the supersonic parts of the fields. The experimental investigations were caned out to show the effects of initial conditions and note geometries on the shock wave characteristics and the turbulences in the flow fields.
This paper describes extensive computer-based analytical studies on the details of unsteady flow behavior around oscillating airfoils in turbomachinery. A comparison was made between the two-and three-dimensional analyses for flow around a NACA0012 airfoil, and the separation vortex structure was examined in detail. From the numerical results, it was found that the separation vortex consisted of large-scale rolls with axes in the span direction, and rib substructures with axes in the stream direction. The three-dimensional analysis could simulate these rolls and ribs, but the two-dimensional analysis was inadequate to realize this vortex structure. In addition, the formation of ribs was found to be affected by the forced oscillation, and the transformation of rolls increased and the vortex structure became more fine as the oscillation frequency increased.
Flow visualization is performed in a two-dimensional smoke tunnel to investigate the flow around flat plate airfoil with miniature tailing-edge flaps. Flow along the lower surface of airfoil, separation bubble in the upsteam corner of flaps, vortex formation of the downstream of flaps and entrainment into the airfoil wake are observed in detail. The flow models for the miniature trailing-edge flaps are proposed.
It is important to disclose the wake flow around cylinders for understanding the mechanisms of heat transfer enhancement in flow networks. An experimental study was performed to visualize the wake flow in the gap between two rectangular cylinders. Square and rectangular cylinders are selected at Reynolds number range of less than 600 in the experiment. The wake flows are visualized at a top view, side views and front views using the fluorescein dye illuminated by a laser light sheet. Different shapes of vortices are shown in the wake flows visualized at three views. Flow visualization allows a better understanding of vortex structures of flow in the gap between two rectangular cylinders.
The turbulence flow around a square or diamond-shaped cylinder has received far less attention than the flow around a circular cylinder. An experimental study was performed to visualize the wake flow behind a diamond-shaped cylinder. Two kinds of aspect ratios d/w=10.0 and d/w=1.0 are selected in the experiment, where d is a depth of the duct and w is a width of the cylinder. The wake flows are visualized at a top view, a side view and front views using the fluorescein dye illuminated by a laser light sheet. It is shown that the three dimensional longitudinal vortices appear in the wake flow behind the diamond-shaped cylinder.
A method for measuring temperature fluctuations in a high-speed flow is developed by the use of a laser-induced fluorescence (LIF) technique. Propagation speed of disturbance can be found by a time lag of cross-correlation functions between the time-dependent LIF signal and a pressure sensor signal at a reference point. The method is applied to a supersonic cavity flow to elucidate the feedback mechanism of self-sustaining flow oscillation.
Large eddy simulation (LES) has been applied to an unsteady three-dimensional flow field in a supersonic cavity with a length-to-depth ratio of 2. The filtered Navier-Stokes equations with a subgrid-scale model of Smagorinsky are solved by an unfactored implicit upwind relaxation scheme based on a TVD formulation with the Roe's approximate Riemann solver. The pressure and velocity vector fields, the shear layer separating from the leading edge of the cavity, and the propagation of the compression and expansion waves in the cavity were visualized to investigate mechanism of self-sustained flow oscillations in the supersonic cavity.
The M5.5 free jet test of the ramjet engine system is conducted at Ramjet Test Facility (RJTF) of NAL Kakuda RC. The ramjet engine system is consisted of the fixed geometry air-intake, ram combustor, and Nozzle. The throat region of the air-intake is visualized with schlieren method. A simple zooming system is used for a small region visualization on large schlieren system.
The laser speckle method was applied to the density gradient measurement of Mach reflection of shock waves. Density gradient in the internal region behind the reflected shock wave was measured by this method, mainly. A shock tube and YAG laser were employed in the experiment. The reference and flow field images were recorded by a high resolution digital camera. The speckle photographs were processed by cross-correlation method by a computer. Displacement of speckle pattern was converted to the density by using a deflection angledensity gradient relation. The shock pattern was extracted from the intensity difference between a reference and flow field images.
It is important to investigate a pressure profile when a shock wave interacts with a reflector from a safety point of view. In this study, experiments are carried out using a shock tube of 50mm diameter and 8m in total length with a cylindrical reflector of 50mm in the observation section. The behavior of reflection process of diffracted shock wave is visualized with the aid of Schlieren techniques. As a result, (i) a pressure histories on the reflector coincides between numerical and experimental results. (ii) The sequential flow-field behind the shock wave is clearified. (iii) An empirical formula of maximum pressure is obtained with a parameter of a energy pen unit area.