Three-dimensional color particle image velocimetry based on a cross-correlation and optical flow method

Rainbow particle image velocimetry(PIV)can restore the three-dimensional velocity field of particles with a single camera;however,it requires a relatively long time to complete the reconstruction.This paper proposes a hybrid algorithm that combines the fast Fourier transform(FFT)based co-correlation algorithm and the Horn–Schunck(HS)optical flow pyramid iterative algorithm to increase the reconstruction speed.The Rankine vortex simulation experiment was performed,in which the particle velocity field was reconstructed using the proposed algorithm and the rainbow PIV method.The average endpoint error and average angular error of the proposed algorithm were roughly the same as those of the rainbow PIV algorithm;nevertheless,the reconstruction time was 20%shorter.Furthermore,the effect of velocity magnitude and particle density on the reconstruction results was analyzed.In the end,the performance of the proposed algorithm was verified using real experimental single-vortex and double-vortex datasets,from which a similar particle velocity field was obtained compared with the rainbow PIV algorithm.The results show that the reconstruction speed of the proposed hybrid algorithm is approximately 25%faster than that of the rainbow PIV algorithm.

Particle Image Velocimetry Measurement of the Flow Field in the Play of the Drilling Pump Valve

The failure of a drilling pump is always due to the break of the drilling pump valve, which is one of the most important but also the weakest parts of the drilling pump. Over the decades, the degradation of drilling pump valves has been investigated extensively and various failure mechanisms have been proposed. However, no experimental test on the fluid has been successfully performed to support some of these mechanisms. In this paper, tests of the flow within the valve play are carried out to investigate the factors resulting in the failure of the valve. In the tests, particle image velocimetry（PIV） technology is employed to measure the flow field distribution of the valve play in the model. From these tests, the distributions of velocity and vorticity of fluid in ＇various valves with different valve angles and different valve lifts are obtained, from which the features of flow fields are derived and generalized. Subsequently, a general rule of the influence of valve angles and valve lifts on the flow velocity is concluded according to chart analyses of maximal velocities and mean velocities. Finally, an analysis is made on the possibility of valve failure caused by erosion and abrasion in a working valve, with the application of the failure mechanisms of drilling pump valves. PIV measurement improves the study on the failure of the drilling pump valve, and the results show good agreement with previous computational fluid dynamics（CFD） simulations.

Particle image velocimetry (PIV) measurements of tip vortex wake structure of wind turbine

Large-view flow field measurements using the particle image velocimetry （PIV） technique with high resolution CCD cameras on a rotating 1/8 scale blade model of the NREL UAE phase VI wind turbine are conducted in the engineering-oriented q53.2 m wind tunnel. The motivation is to establish the database of the initiation and development of the tip vortex to study the flow structure and mechanism of the wind turbine. The results show that the tip vortex first moves inward for a very short period and then moves outward with the wake expansion, while its vorticity decreases with time after being trailed from the trailing edge of the blade tip, and then increases continuously with the rapid rolling-up to form a strong tip vortex. The measurements also indicate that the downstream movement of the tip vortex is nearly linear in the very near wake under the test condition.

3D Particle Image Velocimetry Test of Inner Flow in a Double Blade Pump Impeller

The double blade pump is widely used in sewage treatment industry,however,the research on the internal flow characteristics of the double blade pump with particle image velocimetry（PIV） technology is very little at present.To reveal inner flow characteristics in double blade pump impeller under off-design and design conditions,inner flows in a double blade pump impeller,whose specific speed is 111,are measured under the five off-design conditions and design condition by using 3D PIV test technology.In order to ensure the accuracy of the 3D PIV test,the external trigger synchronization system which makes use of fiber optic and equivalent calibration method are applied.The 3D PIV relative velocity synthesis procedure is compiled by using Visual C＋＋ 2005.Then absolute velocity distribution and relative velocity distribution in the double blade pump impeller are obtained.Test results show that vortex exists in each condition,but the location,size and velocity of vortex core are different.Average absolute velocity value of impeller outlet increases at first,then decreases,and then increases again with increase of flow rate.Again average relative velocity values under 0.4,0.8,and 1.2 design condition are higher than that under 1.0 design condition,while under 0.6 and 1.4 design condition it is lower.Under low flow rate conditions,radial vectors of absolute velocities at impeller outlet and blade inlet near the pump shaft decrease with increase of flow rate,while that of relative velocities at the suction side near the pump shaft decreases.Radial vectors of absolute velocities and relative velocities change slightly under the two large flow rate conditions.The research results can be applied to instruct the hydraulic optimization design of double blade pumps.

Investigation of Unsteady Flow Fields for Flow Control Research by Means of Particle Image Velocimetry

Unsteady three-dimensional flow phenomena must be investigated and well understood to be able to design devices to control such complex flow phenomena in order to achieve the desired behavior of the flow and to assess their performance, even in harsh industrial environments. Experimental investigations for flow control research require measurement techniques capable to resolve the flow field with high spatial and temporal resolution to be able to perceive the relevant phenomena. Particle Image Velocimetry (PIV), providing access to the unsteady flow velocity field, is a measurement technique which is readily available commercially today. This explains why PIV is widely used for flow control research. A number of standard configurations exist, which, with increasing complexity, allow capturing flow velocity data instantaneously in geometrical arrangements extending from planes to volumes and in temporal arrangements extending from snapshots to temporarily well resolved data. With increasing complexity these PIV systems require advancing expertise of the user and growing investment costs. Using typical problems of flow control research, three different standard PIV systems will be characterized briefly. It is possible to upgrade a PIV system from a simple planar to a “high end” tomographic PIV system over a period of time, if sufficient PIV expertise can be built up and budget for additional investments becomes available.

Particle image velocimetry and numerical simulations of the hydrodynamic characteristics of an artificial reef

This article reports a particle image velocimetry study and the comparative results of a numerical simulation into the hydrodynamic characteristics around an artificial reef.We reveal the process of flow separation and vortex evolution,and compare the force terms generated by our artificial reef model.The numerical simulation agrees well with experimental results,showing the applicability of computational fluid dynamics to the hydrodynamics of an artificial reef.Furthermore,we numerically simulate the hydrodynamics of the reef model for seven velocities.The results show that the drag coefficient is approximately 1.21 in a self-modeling region for Reynolds numbers between 2.123×104and 9×104.Therefore,the upwelling height and current width of the flow field do not change significantly when the inflow velocity increases.Our study indicates that computational fluid dynamics can be applied to study the hydrodynamics of an artificial reef and offer clues to its construction.

水流作用下的群桩流场特性PIV试验研究

基于粒子图像测速技术(PIV)开展物理模型试验,对雷诺数Re分别为2400、6000、12000条件下,流向桩心距比为5、横向桩心距比为4时,3×3矩形排列圆桩群桩的局部流场特性开展研究。结果表明,中下游桩间与上中游桩间的流场特性存在显著差异,雷诺数对桩间流场变化影响明显。当Re为2400和6000时,上游中间桩后的尾流涡漩生成长度及回流区长度明显大于两侧边桩,Re为6000时现象更明显,而当Re增大至12000时此现象消失。受上游桩遮蔽作用,中游桩桩后的尾涡强度明显弱于前排桩,回流区面积随之减小。随着雷诺数增大,上游桩桩后尾涡生成长度、回流区尺度逐渐减小。此外,还分析了紊动强度与雷诺切应力在群桩内部平面上的分布变化。本研究以高桩码头桩基础为原型,分析群桩内部流场特性变化,研究结论有助于推进高桩码头泥沙冲淤变化机理的研究,提高高桩码头的安全评估能力。

冲击波流场的PIV速度场修正算法研究

粒子图像测速(particle image velocimetry,PIV)技术是研究分析流动现象产生机制和物理规律的1种重要手段。针对击波管实验中产生的平面冲击波流场,开展了冲击波波阵面及波后速度场图像测量实验,设计并实现了1种结合高斯拟合亚像素与连续性方程的复合图像修正算法,利用该算法对实验原始数据进行了处理分析。结果表明:经本文所提出的算法修正后,波阵面前PIV速度场矢量信息连续,可显示出由于粒子不均匀而不能正确测量的区域信息,提高了速度场信息测量精度,该方法可有效修正存在强间断面的速度场中,由记录图像质量差、粒子播撒不均匀或流动跟随性差等问题带来的速度场计算偏差,为冲击波速度场错误矢量的检测与修正提供了1种简单高效的算法。

Finite Element Numerical Simulation and PIV Measurement of Flow Field inside Metering-in Spool Valve

The finite element method （FEM） and particle image velocimetry （PIV） technique are utilized to get the flow field along the inlet passage, the chamber, the metering port and the outlet passage of spool valve at three different valve openings. For FEM numerical simulation, the stream function ψ-vorticity ω forms of continuity and Navier-Stokes equations are employed and FEM is applied to discrete the equations. Homemade simulation codes are executed to compute the values of stream function and vorticity at each node in the flow domain, then according to the correlation between stream function and velocity components, the velocity vectors of the whole field are calculated. For PIV experiment, pulse Nd： YAG laser is exploited to generate laser beam, cylindrical and spherical lenses are combined each other to produce 1.0 mm thickness laser sheet to illuminate the object plane, Polystyrene spherical particle with diameter of 30-50 μm is seeded in the fluid as a tracing particles, Kodak ES 1.0 CCD camera is employed to capture the images of interested, the images are processed with fast Fourier transform （FFT） cross-correlation algorithm and the processing results is displayed. Both results of numerical simulation and PIV experimental show that there are three main areas in the spool valve where vortex is formed. Numerical results also indicate that the valve opening have some effects on the flow structure of the valve. The investigation is helpful for qualitatively analyzing the energy loss, noise generating, steady state flow forces and even designing the geometry structure and flow passage.

SIMULTANEOUS PIV/PTV MEASUREMENTS OF BUBBLE AND PARTICLE PHASES IN GAS-LIQUID TWO-PHASE FLOW BASED ON IMAGE SEPARATION AND RECONSTRUCTION

A Particle Image Velocimetry (PIV) method based on the image separation andreconstruction with the median filter and triangular Bezier patch was proposed to measure multiplevelocity fields from single-camera images in the present study. The method was examined on syntheticPIV images with the Green-Taylor two-phase vortex flows and the test results showed high accuracyand highly correct tracking percent compared with the exact solution. An experiment of the bubblyjet flow was also conducted as a practical demonstration of the present method. As a result, it isconfirmed from the simulation image examination and the experimental measurement that the proposedmethod shows a good performance in the measurement of bubble and particle phases.

Experimental investigation on flow characteristics in circular tube inserted with rotor-assembled strand using PIV

Rotor-assembled strand works as a typical tube insert to achieve heat transfer augmentation and scale inhibition in a heat exchanger.In this work, the PIV experiment regarding the flow fields in a circular tube inserted with rotor-assembled strand was conducted and the flow characteristics on transverse section and longitudinal section were analyzed.The results showed that swirling flow was produced in the tube inserted with rotors and it was particularly strong within the swing diameter of the rotor on the section that contains the rotor;the average turbulence intensity and the radial velocity were improved notably; the velocity vectors on the longitudinal section remained along the direction of a straight line; both the swirling flow and average turbulence intensity were higher for the rotor with three blades than for the rotor with two blades except that the radial velocity was approximate, but they were all reduced by enlarging the lead of the rotor.Characterization of the flow patterns in a circular tube contributes to understanding the heat transfer efficiency and scale inhibition performance of the rotor-assembled strand and provides guidance for its application.

基于PIV的渐变地表粗糙度对坡面流水动力特性的影响

粗糙度是影响坡面流水动力特性的关键因子,为探究渐变粗糙度影响下坡面流水力特性,采用粒子图像测速技术(particle image velocimetry, PIV)观测并分析3组流量下渐变粗糙床面下坡面流的流速轮廓线、紊动强度、雷诺应力和壁面切应力的变化规律。结果表明:(1)流速随粗糙度增加而减小;拟合无量纲流速得到流速分布对数公式,粗糙度增大与拟合常数A成反比,与积分系数B成正比。(2)渐变地表粗糙度流向紊动强度与光滑床面坡面流变化趋势相似。流向紊动强度随相对水深的增大而减小。随着粗糙度增大,流向紊动强度大小出现非显著性差异。渐变粗糙床面下流向紊动强度符合Nezu经验公式,流量与经验系数成正比。(3)不同流量下,渐变粗糙床面的雷诺应力分布与光滑床面相似。在粗糙度影响下,雷诺应力最大值出现在y/H=0.2~0.4处。随着粗糙度逐渐增加,壁面切应力逐渐增大。综合表明,增加PIV分辨率方法可以适用于坡面流水力特性的研究。探究渐变粗糙度对坡面流的影响,探讨坡面流水动力学特性,为水土保持理论研究提供新思路。

Flow control performance evaluation of a tri-electrode sliding discharge plasma actuator

Tri-electrode sliding discharge(TED)plasma actuators are formed by adding a direct current(DC)exposed electrode to conventional dielectric barrier discharge(DBD)plasma actuators.There are three TED modes depending on the polarity and amplitude of the DC supply:DBD discharge,extended discharge and sliding discharge.This paper evaluates the electrical,aerodynamic and mechanical characteristics of a TED plasma actuator based on energy analysis,particle image velocimetry experiments and calculations using the Navier-Stokes equation.The flow control performances of different discharge modes are quantitatively analyzed based on characteristic parameters.The results show that flow control performance in both extended discharge and sliding discharge is more significant than that of DBD,mainly because of the significantly higher(up to 141%)body force of TED compared with DBD.However,conductivity loss is the primary power loss caused by the DC polarity for TED discharge.Therefore,power consumption can be reduced by optimizing the dielectric material and thickness,thus improving the flow control performance of plasma actuators.

PIV技术在动车组受电弓区域流场测试中的应用

受电弓区域是影响动车组气动阻力和振动噪声的关键部位之一,其流场特性是空气动力学研究的基础。针对该区域的流场研究多以模型试验和数值计算为主,缺乏实车试验数据为其提供数据支撑与对比基础,文中将PIV(Particle Image Velocimetry,粒子图象测速技术)引入受电弓区域流场测试,针对实车上的平面流场信息进行了采集,获得了真实有效的速度及涡量分布情况。

双涡控径向分级燃烧室流场特性

针对新设计的一种双涡控径向分级燃烧室流场特性,采用粒子图像测速仪试验的方式,获得不同压降(1.5%~5.5%)下该型燃烧室不同展向截面和流向截面上流场结构、流线、流速分布和回流区特性。试验结果表明,燃烧室在凹腔内形成了耦合展向涡与流向涡的三维涡系;主燃级旋流器后外旋螺旋流场与中心回流区共同构成三维涡球结构;凹腔与主燃级流场在主燃孔进气作用下相互耦合。随着压降变化,燃烧室冷态流场存在2种流态,压降小于3.5%时,旋流器旋转气流明显强于凹腔气流,凹腔气流被压至外壁流出,与主流掺混较为困难,在火焰筒下游与主流相互作用;压降大于3.5%时,旋流器旋转气流减弱,凹腔气流一同与旋转气流流出并相互作用,凹腔气流往主流掺混相对较为容易。

基于PIV测量的涡轮流量计响应分析

应用粒子成像测速技术获得了涡轮流量计叶片入口流场的速度分布信息,并基于该测量结果,运用T-G模型理论得出流量计的响应。通过与以往所采用的几种典型的入口速度分布计算得到的结果比较分析表明,基于PIV测量的结果更接近于涡轮流量计的真实响应。还比较分析了涡轮入口速度分布对涡轮流量计响应的影响机理,相关结果可望为改进涡轮流量计响应的计算分析方法以及优化设计提供有价值的参考。

气液两相流中气泡运动速度场的PIV分析与研究

粒子图像测速技术(PIV)作为一种无扰、瞬态、全场速度测量方法,已被广泛应用于液体或气体的单相流流速场测定.对于两相流PIV技术,目前还处于起步阶段,本文应用PIV技术的基本原理,对静止液体中的气泡运动速度场进行了分析,并对有关气液两相流测量问题进行了探讨.

分流板对圆柱绕流湍流结构演化影响的实验研究

采用粒子图像测速(Particle Image Velocimetry,PIV)技术实验研究了带分流板的圆柱绕流流动特性,分析了分流板对圆柱绕流湍流结构演化特性的影响。雷诺数为3.9×10^(3),分流板长度L与圆柱直径D之比L/D为0~2.50。实验结果表明,随着L/D从0增大至1.00,圆柱后方回流区长度和回流区面积显著增大;当L/D>1.00时,L/D对圆柱后方回流特性的影响较小。分流板影响圆柱绕流湍流结构的演化特性:当L/D<1.00时,分流板抑制尾涡脱落,斯特劳哈尔数Sr减小,L/D从0增大至1.00,Sr减小了26.34%。此外,圆柱尾涡在分流板后缘诱导形成旋转方向相反的二次涡,二次涡沿分流板向上游运动。1.00≤L/D<2.00时,分流板作用于圆柱尾涡,尾涡发生破碎,形成一些小尺度尾涡。L/D≥2.00时,尾涡附着于分流板上,二次涡主要分布于圆柱后方。随着L/D增大,分流板减小了圆柱后方的湍流脉动强度。

PIV水下流场测试系统试验研究

基于粒子图像测速技术,设计研制了一套适用于水洞洞体内高速、封闭试验条件的流场测量与显示设备.该系统由光源、成像、图像处理与分析、控制和粒子投放等分系统组成,具有复杂环境下全流场的无接触、无扰动、高准确度测量和显示能力,流场测试误差小于2%,可为水下航行器外形设计及其改进提供相关的实测数据.

阀体后90°圆形弯管内部流场PIV分析

利用激光粒子图像速度场测试技术对阀体后90°圆截面弯管的内部流场进行测量,分别在不同阀体开度和流速工况下,获取了弯管内大量高分辨率瞬态速度场数据,并对其进行统计分析,以获取相关流场特征,包括时均速度场、流线图谱及涡量场等.结果表明:阀体后弯管流场存在明显的高速区和低速区,并在特定工况下产生涡流;流场特性随着阀门开度、流速以及截面位置的不同而产生较大的变化.