共查询到19条相似文献,搜索用时 109 毫秒
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数字全息粒子图像测速技术(DHPIV)研究进展 总被引:1,自引:0,他引:1
全息粒子图像测速技术(DHPIV)是当前非常具有发展潜力的非定常三维流场测量技
术,是一种具有点空间分辨力的三维空间三维速度场和时间历程的实验观
测方法和技术. 本文介绍了该项技术(数字全息DH和粒子图像测速PIV)
的发展背景和近20年来的研究进展,并介绍了已测得的非定常复杂流动的初步结果. 详
细论述了DHPIV技术所面临的关键性问题和应用基础问题以及相应的进展:粒子空间场的重建与再现的空间分辨
率问题、粒子定位或位移精度问题、信噪比和数字再现的光学与快速算法以及测量空间的扩
展等问题.同时讨论了数字离轴全息等有关技术的潜力, 介绍了进一步的研究发展方向. 相似文献
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Micro-PIV技术——-粒子图像测速技术的新进展 总被引:7,自引:0,他引:7
Micro-PIV是近年来发展起来的一种微尺度流动测速技术.它是传统PIV测量与光学显微技
术相结合的一种整场、瞬态、定量测量方法, 其基本测速原理与传统PIV相同, 但在示踪粒
子选择、图像获取和处理等方面两者存在较大差别.Micro-PIV突破了传统微尺度流体力学
测量手段的局限性, 使得对微尺度流动元件的研究从过去只能给出流量、阻力特性等有限信
息逐步转向对全流场内流结构的直接测量上, 并且达到了相当高的分辨率和测量精度.本文
对近几年Micro-PIV技术发展状况进行了总结和分析, 论述了Micro-PIV技术与传统PIV的
主要区别以及具体的处理技术, 反映了其在科学与工程中的应用,并对此项技术的发展作了展
望. 相似文献
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由空压机提供的气体通过—排微小直径的喷嘴进入静止水体,形成水气两相流流场。在单相PIV和PTV技术的基础上,研究稀疏气液两相流情况下气泡的速度场分布。PIV算法采用快速傅立叶互相关分析法,而PTV算法需要获得每幅图像中每个气泡的形心,根据连续图像中的粒子对,计算速度。用PIV和PTV两种算法处理求出气泡的速度并对两种方法进行比较,其最终研究成果可应用于流体及多相流的流量测技术,提高我们进行低密度气液两相流相关研究的测量水平。同时为水气两相流的数值分析和理论研究提供流场测试的数据。 相似文献
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本文回顾了流动显示发展的历史,以及它在流体力学研究中所起的作用。根据获取流动信息的方式不同,流动显示技术可分为两大类型。作为近代技术发展的例子,三维非对称流干涉图的定量计算、片光技术、散斑照相术、激光诱导萤光法、多普勒干涉图象显示速度场、光电信号转换激光干涉仪、以及图象处理和计算机产生数字流谱技术均作了简要的介绍。 相似文献
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湍流边界层拟序结构的实验研究 总被引:12,自引:0,他引:12
20世纪60年代后, 先后从流动显示发现了快慢斑、猝发、上升流、下扫流和多种涡
结构等湍流边界层的拟序结构. 它们对湍流边界层的摩阻、传热传质和湍动能的产
生等特性有重要影响. 涡结构是上述拟序结构的核心, 它影响其它拟序结构的发展
和演变. 发卡涡通常被认为是基本涡结构. 发卡涡等涡结构的再生, 是湍流边界层
拟序结构能够自持续的必要的因素.壁面低速流上升产生猝发, 是湍流边界层湍能
的主要来源; 条件采样是测量猝发频率和其它拟序结构出现频率的重要手段. 流动
显示对湍流边界层拟序结构作了大量定性观察, 有许多减阻和增加传热率等应用性
研究在此基础上发展起来. 80年代后, 出现了测量湍流边界层的瞬时流速矢量场的
多热线法和PIV技术, 三维PIV技术可望将来为湍流边界层的实验研究带来重大进
展. 本文评述了流动
显示法、多热线法和PIV技术的优点和不足之处, 以及它们在对湍流边界层拟序结
构的研究中的贡献. 相似文献
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PIV技术在超及高超声速流场测量中的研究进展 总被引:1,自引:0,他引:1
本文分析了超声速流场对测量技术的特殊要求, 归纳了目前将粒子影像测速仪(particle image velocimetry, PIV)技术应用于超声速流场的测量时所面临的主要技术难点以及主要的解决方法, 分析了超声速流场中所用PIV粒子的主要要求、粒子特性、投放方法等, 介绍了PIV技术在超声速、高超声速流场测量中最新的国内外进展, 特别是给出了国内外关于高超声速流场中激波/附面层的相互干扰, 以及高超声速飞行器超燃冲压发动机主要部件内流场的PIV试验研究的最新进展. 相似文献
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用拉格朗日相关结构研究圆盘启动过程的流体输运 总被引:2,自引:0,他引:2
利用粒子成像测速(PIV)技术,得到了圆盘启动涡环流场的速度分布和涡量分布.圆盘启动涡环流场的有限时间李雅普诺夫指数场(Finit-time Lyapunov exponents,FTLE)以及拉格朗日相关结构(Lagrangian coherent structures,LCS)被计算出来.基于圆盘启动涡环流场的有限时间李雅普诺夫指数场以及拉格朗日相关结构,通过跟踪流体质点,对圆盘启动涡环流场的输运情况进行了分析.在圆盘启动涡环形成过程中,流体发现被圆盘和相互排斥的拉格朗日相关结构分成三部分.剪切流窗口(vorticity-flux window)被发现,涡量流通过剪切流窗口进入涡核.涡环的非定常边界被确定,它由相互排斥的拉格朗日相关结构背风面、圆盘以及剪切流窗口组成. 相似文献
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Melanie Voges Manfred Beversdorff Chris Willert Hartmut Krain 《Experiments in fluids》2007,43(2-3):371-384
As part of an ongoing research project the performance and internal flow field of a high-pressure ratio centrifugal compressor
is being investigated. Based on previous, primarily, point-wise laser-optical measurements the compressor was redesigned and
resulted in an improved impeller and diffuser with a single-stage pressure ratio of 6:1 at 50,000 rpm. Current research activities
involve the use of particle image velocimetry (PIV) to analyze and further improve the understanding of the complex flow phenomena
inside the vaned diffuser given the capability of PIV of capturing spatial structures. The study includes phase-resolved measurements
of the flow inside a diffuser vane passage with respect to the impeller blade position. Both, instantaneous and phase-averaged
velocity fields are presented. The flow field results obtained by PIV are to be used for future validation of the related
CFD calculations, which in turn are expected to lead to further improvements in compressor performance. In addition, the potential
of stereo PIV for this type of turbomachinery application could be successfully demonstrated. 相似文献
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A novel PIV technique for measurements in multiphase flows and its application to two-phase bubbly flows 总被引:2,自引:0,他引:2
A new experimental procedure for performing simultaneous, phase-separated velocity measurements in two-phase flows is introduced. Basically, the novel particle image velocimetry (PIV) technique is a combination of the three most often used PIV techniques in multiphase flows: PIV with fluorescent tracer particles, shadowgraphy, and the digital phase separation with a masking technique. The combination of these three independent measurement techniques is achieved by shifting the background intensity of a PIV recording to a higher, but uniform gray value level. In order to combine the advantages of these multiphase-PIV methods, a new PIV set-up was developed. With this set-up the velocity distributions of the two phases are measured simultaneously with only one b/w camera. This experimental set-up is aimed at providing a means for characterizing the modification of turbulence in the liquid phase by bubbles. This phenomenon is often called "pseudo-turbulence". 相似文献
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Matthieu RoudetAnne-Marie Billet Frédéric RissoVéronique Roig 《Experimental Thermal and Fluid Science》2011,35(6):1030-1037
In this work we test a methodology for PIV measurements when a large field of view is required in planar confined geometries. Using a depth of field larger than the channel width, we intend to measure the in-plane variations of the velocity of the fluid averaged through the width of the channel, and we examine in which operating conditions this becomes possible. Measurements of the flow through a narrow channel by PIV are challenging because of the strong velocity gradients that develop between the walls. In particular, all techniques that use small particles as tracers have to deal with the possible migration of the tracers in the direction perpendicular to the walls. Among the complex mechanisms for migration, we focus on the so called Segré-Silberberg effect which can lead to transverse migration of neutrally buoyant tracers of finite size. We report experimental PIV measurements in a Hele-Shaw cell of 1 mm gap, which have been carried out by using neutrally buoyant tracers of size around 10 μm. By considering steady flows, we have observed, in particular flow regimes, the effect of an accumulation of the tracers at a certain distance to the wall due to the so called Segré-Silberberg effect. The particle migration is expected to occur at any Reynolds numbers but the migration velocity depends on the Reynolds number. A significant migration therefore takes place each time the observation duration is large enough compared to the migration time. For a given observation duration, the tracers remain uniformly distributed at low Reynolds numbers whereas they all accumulate at the equilibrium position at large ones. When using volume lighting, the PIV algorithm provides the average velocity of the flow through the gap at low Reynolds number, while it leads to the velocity of the flow at the equilibrium position of the tracers at large Reynolds numbers. By considering unsteady flows, we have observed that the migration does not occur if the timescale of flow variation is short compared to the time required for the parabolic flow to develop across the gap. In this case, there is no transverse velocity gradient and the PIV algorithm provides the fluid velocity. Altogether, these results allow us to propose guidelines for the interpretation of PIV measurements in confined flow, which are based on the theoretical predictions of the tracer migration derived by Asmolov [1]. 相似文献
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R. Perrin M. Braza E. Cid S. Cazin F. Moradei A. Barthet A. Sevrain Y. Hoarau 《Flow, Turbulence and Combustion》2006,77(1-4):185-204
The main objective of the present experimental study is to analyse the turbulence properties in unsteady flows around bluff body wakes and to provide a database for improvement and validation of turbulence models, concerning the present class of non-equilibrium flows. The flow around a circular cylinder with a low aspect ratio () and a high blockage coefficient () is investigated. This confined environment is used in order to allow direct comparisons with realisable 3D Navier–Stokes computations avoiding ‘infinite’ conditions. The flow is investigated in the critical regime at Reynolds number 140,000. A cartography of the velocity fields in the near wake of the cylinder is obtained by PIV and Stereoscopic PIV techniques. Statistical means and phase-averaged quantities are determined. Furthermore, POD analysis is performed on the data set in order to extract coherent structures of the flow and to compare the results with those obtained by the conditional sampling technique. The Reynolds stresses, the strain-rate and vorticity fields as well as the turbulence production terms are determined. 相似文献
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