A realistic coronary artery phantom for particle image velocimetry

Myocardial infarction results from the rupture of an atherosclerotic plaque, which occurs in response to both mechanical stress and inflammatory processes. In order experimentally observe flow into atherosclerotic coronary artery morphologies, a novel technique for molding realistic compliant phantom featuring injection-molded inclusions and multiple layers has been developed. This transparent phantom allows for particle image velocimetry (PIV) flow analysis and can supply experimental data to validate computational fluid dynamics algorithms and hypothesis.     

A new particle image velocimetry technique for three-dimensional flows

A PC-based machine vision system for obtaining three-dimensional particle co-ordinates using a single camera is presented. Based on photogrammetric imaging, this system uniquely combines the advantages of stereo and orthogonal views to determine the accurate locations of the particles. A 3D cross-correlation algorithm has been implemented to follow the particles from frame to frame and compute the velocity vectors. Experiments have been carried out to obtain the velocity profiles in a cubical test section with an offset inlet and outlet. The results obtained from the experimental investigation were compared with numerical simulation data obtained from FLUENT and STAR-CD.     

用于层析粒子图像测速的模拟粒子场成像

对层析粒子图像测速(PIV)技术中示踪粒子成像部分进行理论分析,并结合真实风洞的相应参数,通过搭建模拟粒子成像平台的方法来进行研究。设计了一套体积为80 mm×100 mm×100 mm的激光照明系统,以提供粒子场的入射光强。建立了示踪粒子的三维成像模型,从而得到层析PIV系统的模拟图像。分析了影响PIV系统成像质量的相关因素。在单像素粒子数为0.007 7的情况下,通过真实粒子图像和模拟粒子图像比较,验证了该方法的正确性。     

Time resolved particle image velocimetry

The temporal evolution of the velocity field of an unsteady fluid flow can be tracked by combining Particle Image Velocimetry (PIV) and high speed photography. Two alternative techniques for PIV are discussed: the classical light sheet technique and a method which makes use of the light scattered in forward direction. We applied time resolved PIV to investigate the flow around cavitation bubbles during their collapse near a solid boundary. The light source was an argon laser with an external acousto-optic deflector which produces series of short pulses. Using a drum camera for high speed photography, we achieved a temporal resolution of10 kHz and a spatial resolution of better than2 points/mm². Velocities could be determined without directional ambiguity in a range from2 m/s to30 m/s.     

Fibre-optic beam delivery systems for particle image velocimetry

The role of fibre-optics in the formation of light sheets for particle image velocimetry is reviewed, concentrating on the power handling capacities of fibres and their effect on laser beam quality. It is shown that when continuous wave lasers are used, chopped to form a pulsed light sheet, then it is feasible to use a single multimode optical fibre to deliver the beam. Conversely, with Q-switched lasers, the peak power densities are so high that to achieve an adequate compromise between pulse energy and beam quality, delivery systems based on bundles of multimode fibres have been developed.     

Modern developments in particle image velocimetry

This paper summarises the development of particle image velocimetry (PIV) over the last decade and describes its applications as an effective measuring technique for mapping complex flow fields. A review of work in the field is given. Current aerodynamic and hydrodynamic investigation by the authors exploiting the method are described and used as illustration.     

Development of particle image velocimetry for multiphase flow diagnostics

This paper discusses the suitability of PIV for measuring simultaneously the velocity field of every phase and the size and concentration field of the disperse phases in multiphase flows. Velocity and disperse phase information are both inferred either directly from the Young’s fringe pattern (far field diffraction function) or from its 2-D Fourier transform (autocorrelation function). In the first case, the velocity is inferred from the orientation and spacing of the fringes while the disperse phase size is inferred from the size of the diffraction halo that modulates the fringes. In the second case, the velocity and particle shape are related to the position and shape of the strongest autocorrelation peaks, respectively. Particle sizes are used to discriminate between phases on the velocity measurements. The technique has been demonstrated on a high speed air-particle flow, where the potential for determining air velocities and particle size and velocities are shown.     

Optical evaluation methods in particle image velocimetry

Application of particle image velocimetry (PIV) techniques for measurement of fluid velocities typically requires two steps. The first of these is the photography step, in which two exposures of a particle field, displaced between the exposures, are taken. The second step is the evaluation of the double-exposure particle pattern and production of appropriate particle velocities. Each of these steps involves optimization, which is usually specific to the experiment being conducted, and there is significant interaction between photographic parameters and evaluation characteristics. This paper will focus on the latter step, that of evaluation of the double-exposure photograph. In several parts of a PIV system, some performance advantage may be obtained by increasing use of optical processing over conventional digital image processing. Among the processes for which a performance advantage may be obtained are parallel or multiplex image interrogation and the evaluation of the Young's fringe pattern obtained from the scattered pattern from the double-exposure photograph. This paper will discuss parallel image interrogation and compare the performance of optical and numerical Fourier transform analysis of Young's fringes using speckle images.     

Holographic particle image velocimetry (HPIV)

There are several well-known difficulties in forming and analysing holographic particle data in the micrometre and sub-micrometre size range. This paper suggests that these problems can be overcome by using a combination of research techniques. Firstly, it has been found that it is possible to record images of sub-micrometre particles using conventional photographic materials. Essentially, a diffraction limited optical component has been used to provide aberration free particle images. Secondly, the sensitivity of the holographic material has been increased with the use of specialized holographic processing chemicals. Thirdly, it has been found that it is possible to encode holoraphically double, slightly displaced, particle images using a pulse laser. Thus, Young's fringes can be obtained directly from the stored holographic data and the particle velocity can be measured directly from the hologram. Fourthly, the holographic particle data can be automatically analysed using a software programme. Finally, since the data is stored holographically, it is possible to obtain instantaneous three-dimensional particle velocity. This paper demonstrates that it is possible to perform holographic particle image velocimetry automatically, with only a small amount of pre-processing.     

A novel particle tracking velocimetry method for complex granular flow field

Particle tracking velocimetry(PTV) is one of the most commonly applied granular flow velocity measurement methods. However, traditional PTV methods may have issues such as high mismatching rates and a narrow measurement range when measuring granular flows with large bulk density and high-speed contrast. In this study, a novel PTV method is introduced to solve these problems using an optical flow matching algorithm with two further processing steps. The first step involves displacement correction, which is used to solve the mismatching problem in the case of high stacking density.The other step is trajectory splicing, which is used to solve the problem of a measurement range reduction in the case of high-speed contrast The hopper flow experimental results demonstrate superior performance of this proposed method in controlling the number of mismatched particles and better measuring efficiency in comparison with the traditional PTV method.     

Brownian motion and correlation in particle image velocimetry

In particle image velocimetry applications involving either low velocities or small seed particles, Brownian motion can be significant. This paper addresses the effects of Brownian motion. First, general equations describing cross-correlation particle image velocimetry are derived that include Brownian motion. When light-sheet illumination particle image velocimetry (PIV) is used Brownian motion diminishes the signal strength. A parameter describing this effect is introduced, and a weighting function describing the contribution to the measured velocity as a function of position is derived. The latter is unaffected by Brownian motion. Microscopic PIV Brownian motion also diminishes the signal strength. The weighting function for microscopic PIV is found to depend on Brownian motion, thus affecting an important experimental parameter, the depth of correlation. For both light-sheet illumination and microscopic PIV, a major consequence of Brownian motion is the spreading of the correlation signal peak. Because the magnitude of the spreading is dependent on temperature, PIV can, in principle, be used to simultaneously measure velocity and temperature. The location of the signal peak provides the velocity data, while the spreading of the peak yields temperature.     

激光散斑测速和粒子像测速技术中的频谱模板方法

文中提出了用流场的一次曝光像的强度谱作为模板提取杨氏条纹，以获取尖锐的自相关分布的方法，并给出了该方法用于激光散斑测速和粒子像测速技术的计算机模拟结果以及粒子像测速的应用例子。     

Echo particle image velocimetry technique and its applications

Developments of many cardiovascular problems have been shown to have a close relationship with arterial flow conditions.However,current ultrasound/Doppler imaging techniques cannot resolve the complex nature of arterial blood flow.We have recently developed a novel contrast-based echo particle imaging technique(Echo PIV) without angel dependence for non-invasively measuring multi-component flow vectors.This study introduces the Echo PIV principles,system characterization and utility examination to characterize hemodynamics in pipe laminar flow and rotating flow.Echo PIV measurement results show its capability to resolve the complex hemodynamics including proximal flow velocity vectors,and velocity mapping. The Echo PIV method provides an easy,direct and accurate means of quantitatively yet non-invasively characterizing the complex vascular hemodynamics.     

超声粒子图像测速技术及应用

心血管疾病的产生与动脉血流的流动状况密切相关。然而,目前普遍应用的超声多普勒成像技术不能精确测量复杂血流流场信息。本文提出了一种基于超声造影微泡的超声全流场粒子图像测速技术,能够获得多维流速速度信息,且不依赖于声束与速度向量之间的夹角。本文首先着重阐述了超声全流场粒子测速技术的基本原理以及系统组成,并对直管流和旋转流场流体动力学特性进行了实验测试研究,实验结果表明本技术能够测量全流场速度,并可作为表征复杂血流流场的有力手段。     

An image-shifting technique based on grey-scale classification for particle image velocimetry

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.     

Double exposure, multiple-field particle image velocimetry for turbulent probability density

A particle image velocimeter method is described in which double exposed fields of particles moving in a two-dimensional slice of a steady turbulent flow are photographed repeatedly to build up a statistical ensemble of flow field realizations on a single photographic plate. Each interrogation spot on the plate contains a sample of the probability density function of the two components of velocity that lie in the photographic object plane, assuming paraxial photography. Theory is developed showing how this sample can be measured by two-dimensional spatial correlation analysis, followed by deconvolution to remove the effects of finite particle image size. The probability density measurements are biased inherently against large velocities, but these effects can be minimized and/or corrected.     

Acoustic streaming in lithotripsy fields: preliminary observation using a particle image velocimetry method

This study considers the acoustic streaming in water produced by a lithotripsy pulse. Particle image velocimetry (PIV) method was employed to visualize the acoustic streaming produced by an electromagnetic shock wave generator using video images of the light scattering particles suspended in water. Visualized streaming features including several local peaks and vortexes around or at the beam focus were easily seen with naked eyes over all settings of the lithotripter from 10 to 18 kV. Magnitudes of the peak streaming velocity measured vary in the range of 10-40 mm s(-1) with charging voltage settings. Since the streaming velocity was estimated on the basis of a series of the video images of particles averaged over 1/60s, the time resolution limited by the video frame rate which is 1-2 orders of magnitude larger than driving acoustic activities, measured velocities are expected to be underestimated and were shown a similar order of magnitude lower than those calculated from a simple theoretical consideration. Despite such an underestimation, it was shown that, as predicted by theory, the magnitude of the streaming velocity measured by the present PIV method was proportional to acoustic intensity. In particular it has almost a linear correlation with peak negative pressures (r=0.98683, p=0.0018).