共查询到20条相似文献,搜索用时 491 毫秒
1.
Velocity and density field measurements based on image processing of laser speckle or pseudo-speckle pattern have been developed. Laser speckle velocimetry (LSV) or white-light speckle velocimetry (WSV), which corresponds to a high-image-density PIV, gives a local velocity vector map or whole field velocity contour map of a two-dimensional flow field seeded densely with fine particles. This technique has an advantage in high-speed flow measurement without limit of frame rate except for directional ambiguity. New techniques of laser speckle photography and laser speckle interferometry by means of digital image processing have been developed recently for density field measurements. In laser speckle photography, a local density gradient vector map is reconstructed by cross-correlation evaluation between the reference and the object speckle patterns. In laser speckle interferometry, an equi-density contour map is reconstructed by image subtraction between the reference and the object interferometric speckle patterns. 相似文献
2.
3.
基于时间分辨的粒子图像测速技术(time-resolved particle image velocimetry, TR-PIV)是一种广泛应用的非接触式二维瞬时流场可视化测量技术。为了得到流场精细的瞬态空间结构和演变过程,提出了一种利用多光谱成像技术来提高流场测量的时间分辨率的方法。利用多个不同波长的脉冲激光照明流场中的同一测量区域,使用多光谱成像系统采集不同波长的粒子图像,经过图像分离,判决计算产生速度矢量场。为了验证这一原理的可行性,使用三种不同波长(488,532和632.8 nm)的单色光谱脉冲搭建了一套基于多光谱成像的TR-PIV系统,通过多波长激光脉冲之间时序的精确控制,将两帧图像之间的时间间隔从10 ms缩短至3.4 ms,时间分辨率提高了3倍。结果表明基于多光谱的TR-PIV测量系统在保持PIV技术瞬时全场测量特点的同时,时间分辨率大为提高。 相似文献
4.
Study of Spatial Hole Burning in Distributed Phase-Shifted Distributed Feedback Semiconductor Lasers 下载免费PDF全文
In this
paper,the Huygens-Fresnel principle is restudied by means of wavelet analysis firstly,this
builds the basis of the theory for wavelet optics.Then the theory of wavelet analysis is
used to analyze the filtering in spatial domain and spatial frequency domain.For
example,it gives the space variable processing for the filtering with wavelet in spatial
domain,the match filtering for the filtering with wavelet in spatial frequency domain and
a single slit and a round aperture for the wave-front filtering.The feasibility for
treating the problems in optical field with wavelet transform is discussed,and the
theoretical frame of wavelet optics is built. 相似文献
5.
6.
The experimental flow visualization tool, Particle Image Velocimetry (PIV), is being extended to determine the velocity fields in three-dimensional, two-phase fluid flows. In the past few years, the technique has attracted quite a lot of interest. PIV enables fluid velocities across a region of a flow to be measured at a single instant in time in the whole volume (global) of interest. This instantaneous velocity profile of a given flow field is determined by digitally recording particle (microspheres or bubbles) images within the flow over multiple successive video frames and then conducting flow pattern identification and analysis of the data. This paper presents instantaneous velocity measurements in various three-dimensional, bubbly two-phase flow situations. This information is useful for developing or improving existing computer constitutive models that simulate this type of flow field. It is also useful for understanding the detailed structure of two-phase flows. 相似文献
7.
The ventilation flow in a heating, ventilation and air conditioning (HVAC) module of a passenger car was investigated experimentally.
Three different ventilation modes with varying temperature mode were tested to study the effect of ventilation mode on the
velocity field inside the HVAC module. For each mode, more than 450 instantaneous velocity fields were measured using a particle
image velocimetry (PIV) velocity field measurement technique. The instantaneous velocity fields were ensemble averaged to
obtain the spatial distribution of mean velocity and spanwise vorticity. The present work highlights the usefulness of the
PIV technique for the analysis of the flow inside an HVAC module. The experimental results can be used not only to understand
and improve the ventilation flow of an HVAC module but also to validate numerical predictions. 相似文献
8.
等离子体激励器电极组相位不同便产生多相等离子体气动激励,建立了粒子图像测速仪流场参数测试系统,利用粒子图像测速仪技术,研究了非对称布局等离子体气动激励诱导空气流动特性,分析了多相等离子体气动激励对诱导空气流动速度的影响。结果表明:粒子图像测速仪流场测试系统能够准确地反映等离子体气动激励诱导空气流动的流场空间结构,等离子体气动激励诱导空气流动是平行于激励器的近壁面射流,多相等离子体气动激励能够增大等离子体气动激励诱导气流速度,或者使等离子体气动激励影响流场区域增大。粒子图像测速仪系统是深入研究等离子体气动激励的流场结构最佳的方式之一。 相似文献
9.
M.P. Arroyo T. Yonte M. Quintanilla J.M. Saviron 《Optics and Lasers in Engineering》1988,9(3-4):295-316
We present here an application of particle image velocimetry (PIV) to the analysis of the Rayleigh-Be´nard convection patterns in small ☐es, in which a low power laser (5 mW He-Ne) has been used and photographs with a high number of exposures have been taken. Parameters which affect the quality of photographs are analyzed and related with the number of exposures.
The data reduction is made by fringe analysis (point-by-point technique) and by spatial filtering (whole-field technique). The fringe analysis is made with a1 − D integration method, which has been fully automated in the way described here.
The velocity field is numerically processed in order to obtain some additional information (like flow rates, vorticity, streamlines, …) which is relevant in fluid mechanics.
Finally, results obtained from an application of the whole process to the study of motion in the mid-plane of a Rayleigh-Be´nard cell are shown. 相似文献
10.
气液两相流速度及粒径分布激光干涉测量方法的研究 总被引:1,自引:0,他引:1
为了实现对气液两相流的粒子粒径、空间分布及其速度测量。对激光干涉气液两相流测量技术(ILIDS)进行了深入研究,该技术是一种应州于气液两相流测量的新技术,其主要优点是不干扰流场和颗粒粒径、位置测量精度高。基于该技术所开发的图像自动处理方法可以利用普通粒子成像测量技术系统拍摄气液两相流的激光散射干涉图像。并利用图像卷积定位、傅里叶变换频率分析及其图像互相关测速等图像处理手段从干涉图像中自动提取粒子的位置、直径和速度信息。为了验证该方法的测量精度,对喷嘴生成的气水两相流进行了测量实验,得到了喷嘴出口处不同区域的粒径、速度矢量的空间分布,并将测得的速度矢量与用粒子成像测量技术方法测得的结果进行对比,证明两种方法测量的平均速度差别仅为0.38%。 相似文献
11.
A gun-type burner is a widely used oil burner for industrial and domestic applications. The oil is pressure-atomized and mixed
with air generating a recirculating, swirling flow. Because of the surrounding flame, fuel droplets evaporate, being difficult
to obtain information on droplets’ dynamics. Several laser techniques have been applied to this burner for spray diagnosis.
PDA provides information about droplet size and velocity but can say little about the instantaneous spatial structures in
the flow. Planar laser techniques as PIV can describe the 2D instantaneous spatial structures, but cannot provide information
about the 3D structures in the flow. Then Stereoscopic PIV was applied. This technique allows us to measure the full 3D velocity
vector map in a whole fluid plane. This paper has a double purpose. Firstly, to visualize the 3D structures which are present
in the burner; secondly, to show that Stereoscopic PIV is an applicable technique for the diagnosis of an evaporating spray. 相似文献
12.
Zero-order and twin images are a serious obstacle in achieving a high-quality output in in-line digital holography (DH). They decrease the useful bandwidth of the off-axis DH. Over the years the twin image removal problem was approached both by instrumental and numerical means. The paper provides an extended survey of the proposed solutions with their pros and cons as a guide for further advance in this field. Processing of a single spatial carrier fringe pattern involves spatial filtering in the frequency domain, spatial phase-shifting (PS) or wavelet transform. A point source digital holographic microscopy (DHM), introduction of calibration measurements or various modifications of PS technique are instrumental solutions to the twin image problem for in-line DH. Numerical solutions to the same problem include iterative and non-iterative approaches, diffraction-based and inverse problem solutions, reconstruction of purely real or phase objects and of complex objects, reconstruction of plane and volume objects. Elimination only of the zero-order image relies on non-linear filtering or additional calibration measurements. 相似文献
13.
14.
D.D. Udrea P.J. Bryanston-Cross W.K. Lee M. Funes-Gallanzi 《Optics & Laser Technology》1996,28(5):389-396
This article presents two algorithms for spatial processing of low seeding density PIV (particle image velocimetry) images which lead to sub-pixel precision in particle positioning. The particle centres are estimated to accuracies of the order of 0.1 pixel, yielding 1% error in velocity calculation. The first algorithm discriminates valid particles from the rest of the image and determines their centres in Cartesian coordinates by using a two-dimensional Gaussian fit. The second algorithm performs local correlation between particle pairs and determines instantaneous two-dimensional velocities. The methods have been applied initially to simulated data. Gaussian noise and distortion has then been added to simulate experimental conditions. It is shown that, in comparison with conventional methods, the new algorithms offer up to an order of magnitude higher accuracy for particle centre estimation. Finally, the Gaussian fit approach has been used to map an experimental transonic flow field from the stator trailing edge wake region of a cascade with an estimated error of 1%. The experimental results are found to be in good agreement with previous theoretical steady-state viscous calculations. 相似文献
15.
Laser velocimetries, such as LDV or laser-2-focus (L2F) velocimetry, have been widely used for a flow measurement in a high-speed rotating impeller. A particle image velocimetry (PIV) is one of the popular velocity measurement techniques for the ability to measure a velocity field. And a PIV offers an extensive velocity field in an extremely shorter measurement time than the laser velocimetries. In the present experiment, a PIV was applied to a flow measurement in a transonic centrifugal impeller. A phase locked measurement technique every 20% blade pitch was performed to obtain a velocity field over one blade pitch of the inducer. The measured velocity field at the inducer of impeller clearly showed a shock wave generated on the suction surface of a blade. The validity of the present technique was also discussed. 相似文献
16.
JIN Dawei WANG Yuanyuan WANG Weiqi 《声学学报:英文版》2007,26(3):261-268
In medical Doppler ultrasound systems, a high-pass filter which is usually employed to filter wall clutter components, will remove the information of the low velocity blood flow. To extract intact Doppler ultrasound blood signals, a novel approach is proposed based on the spatially selective noise filtration. The wall signals are firstly estimated by the spatially selective noise filtration from wavelet spatial correlation property. Then the wall clutters are exactly obtained by a wavelet threshold de-noising technique which eliminates the residual blood flow signals. Finally the intact blood flow signals are achieved by subtracting the wall signals from the mixed signals. This approach is applied to both computer simulated and in vivo carotid Doppler ultrasound signals. The experiment results show that the wavelet space based approach can exactly extract the blood flow signals, and achieve about 45% lower results in the mean absolute error than that of the high-pass filtering. This approach is expected to be an effective method to remove the wall clutters in Doppler ultrasound systems. 相似文献
17.
An image-shifting technique based on grey-scale classification for particle image velocimetry 总被引:3,自引:0,他引:3
The image-shifting techniques are used to overcome the directional ambiguity of particle image displacement in the measurement of particle image velocimetry (PIV). This paper proposes an image-shifting technique based on grey-scale classification for PIV. By calculating the unified grey-scale statistical frequency of each interrogated unit, the directional ambiguity is resolved without any special requirement of the camera, and the particle image displacement is calculated synchronously. This image-shifting technique can be realized by controlling the difference in the light intensity of two lasers. Using this new technique, a PIV system was developed and used to measure the diesel spray flow. The displacement vector map of fuel particle in the spray flow was obtained, and the structure of the spray flow was investigated. The application confirmed that the image-shifting technique is viable and effective. 相似文献
18.
The purpose of this study is to understand the aerodynamic noise source distribution around a rotating fan blade by measuring
the noise signal and velocity field around the blade. The local noise-level distribution over the fan blade is measured by
microphone arrays, and the flow field is visualized by smoke and phase-averaged PIV measurement. The noise source distribution
is examined by cross-correlation analysis between noise signal and velocity fluctuation. It is found that the noise source
is located near the rotating fan blade, especially around leading and trailing edges. The separation and reattachment of flow
are observed near the leading edge, and the tip vortices and vortex shedding are found near the trailing edge. The cross-correlation
distribution of the noise signal and the radial velocity fluctuation shows large magnitude in the correlated regions, which
indicates the noise generation by the formation of vortex structure around the blade. 相似文献
19.
To analyze the complex three-dimensional flow structure of an axial flow fan and determine the validity of its application, PIV is used to provide detailed space and time resolved experimental data for understanding and control of flow field. The high resolution stereoscopic PIV system was successfully employed in this study for the investigation of flow structure around the axial flow fan. Using the once-per-revolution signal from the rotor, image fields were captured at a fixed position of the blades and hence provides the ability to do phase-averaging. The three-dimensional instantaneous velocity fields, phase-averaged velocity fields, instantaneous and mean vorticity distributions of the stereoscopic PIV measurement results were represented at typical planes of the flow field. Phaseaveraged velocity fields were calculated based on 200 frames of the instantaneous stereoscopic PIV measurement results. From the velocity distribution, the vorticity and turbulent intensity distribution, which are known to be major factors of fan noise, were calculated and its diffusion was discussed as they travel downstream. From the reconstructed three-dimensional velocity iso-surface at 8 cross planes of the outlet flow fields, the three-dimensional features can be seen clearly. 相似文献