简易粒子图像测速(PIV)技术开发与优化技巧

粒子图像测速(PIV)技术是一种瞬态流动平面二维速度场测试技术,在细部流场实测领域得到重视,但是成熟的PIV产品价格高昂。鉴于此,介绍了一种简易的PIV装置,主要由高速摄像机、激光发射器、柱面透镜和示踪粒子构成,以较低成本即可基本实现商业用PIV产品的功能。为了验证简易PIV性能,设计了PIV简易装置,采用Fluent软件模拟,并结合PIV技术对比分析了简易PIV装置的优缺点,同时对影响结果的粒径大小和粒子跟随性进行了优化。结果表明,简易PIV装置适宜选用玉米粉作为示踪粒子,并需要根据示踪粒子跟随性所能达到的最大进口水流速度选择高速摄像机的帧率,最终能够较好地实现流场实测,进而达到对PIV技术进行开发和优化的目的,其分析结果将为后续研究者提供参考。     

流速梯度对悬浮颗粒脉动强度的影响

从简化的颗粒运动方程出发，分析了在剪切流场中颗粒脉动强度和流体脉动强度之间的关系。结果表明，由于纵向时均流速的垂线分布梯度的作用，颗粒在两个方向上的脉动强度均可能超过相应的流体脉动强度。     

平面旋转水流中颗粒运动分离 特性的研究

本文旨在通过数值和实验方法,研究固体颗粒在旋转水流中发生分离运动的特性;通过4阶 龙格一库塔法求解颗粒运动方程,求出不同时刻颗粒运动方向与水流运动方向的分离角度。然后,在 一个匀速旋转的圆柱形平台上,对不同颗粒粒径、密度和平台转速,进行了不同参数组合的实验。实 验结果与数值解吻合良好。最后,利用多元回归方法,提出了误差在25%左右的预估公式。     

离心力分离液固两相流

本文对旋流器中流体的运动微分方程、流线方程、速度分布、压力分布、能量损失进行了分析。重点是阐述了水力旋流器分离液固两相流颗粒运动状况,研究了不同流态下的颗粒相对运动速度,可除去的最小颗粒粒径以及除砂(泥渣)率的估算方法。     

PIV and PTV measurements in hydro-sciences with focus on turbulent open-channel flows

PIV is one of the most popular measurement techniques in hydraulic engineering as well as in fluid sciences. It has been applied to study various turbulent phenomena in laboratory experiments related to natural rivers, e.g., bursting phenomena near the bed, mixing layers observed at confluences, wake turbulence around dikes and piers, and so on. In these studies, PIV plays important roles in revealing the space-time structure of velocity fluctuations and coherent vortices. This review article focuses particularly on the applications of PIV to turbulent open-channel flows, which have been conducted for the past decade in Hydraulics Laboratory of Kyoto University. In Section 2, we introduce our experimental setup and PIV/PTV algorithm. In Section 3, we apply the PIV measurements to reveal turbulence characteristics and coherent structures in open-channel flows as well as in vegetated canopy flows. For complex flow situations, various applications of PIV to compound open-channel flows and wind-induced water waves are considered to reveal coherent vortices. In Section 4, we discuss some advanced PIV measurements in open-channel flows. The free-surface-elevation fluctuations and velocity components were measured simultaneously with two sets of cameras to examine phase-averaged parameters of turbulence. A multi-layer scanning PIV was developed to reveal 3D turbulence structure in compound open-channel flows. Our discriminator PIV/PTV was applied successfully to sediment-laden open-channel flows and revealed the fluid/particle interaction and the relationship between coherent structures and sediment concentration. Finally, we conducted simultaneous measurements of velocity and dye concentration with a combination of PIV and LIF in vegetated open-channel flow, which enables us to examine turbulent scalar flux of a passive contaminant.     

水沙流中的泥沙悬浮(Ⅰ)

近年来用于研究含沙水流中悬浮颗粒垂向浓度分布的理论已有很多。连续性假设虽然被证明在描述流体运动时非常成功，但却不足以描述含沙水流中的离散固体颗粒运动。随机模型能用于研究流动中单个颗粒的运动，但很难解释固体颗粒之间相互作用的机制。本文对各种传统理论进行了综合分析和比较，对已有的典型颗粒浓度分布的一般性解释进行了讨论，并据此提出了今后研究的重点。     

一种改进的粒子图像测速混合算法研究

粒子图像测速技术作为一种新的流场测速方法能够在不干扰流场的情况下获得整个流场的速度信息。粒子图像测速技术最关键的步骤在于粒子匹配。针对粒子密度分布不均匀、流场不同等实际情况,提出了混合算法,即结合互相关和松弛算法能够更准确地搜索粒子,进而对粒子进行匹配。对3种匹配算法的匹配概率进行比较分析,发现混合算法能更准确地分析粒子的运动状态,减少错误矢量的产生;另外,对松弛算法进行改进,通过优化筛选加权因子发现改进的松弛算法在运行速度上相比原始算法有了较大提高,匹配率与原始算法基本一致。     

粒子驱动流体运动

本文建立了粒子体积浓度不是很大的情况下粒子驱动流体运动的控制方程,而后对静止流体中由粒子群沉降驱动的流体运动进行了探讨,最后,对由圆形喷口喷出的异质粒子驱动的流体轴对称射流进行了分析。     

EXPERIMENTAL RESEARCH OF FLOW STRUCTURE IN A GAS-SOLID CIRCULATING FLUIDIZED BED RISER BY PIV

Particle Imaging Velocimetry (PIV) techniques were applied to investigate the particle motion and cluster properties in a gas-solid two-phase flow in a circulating fluidized bed riser. Visual images and micro-structure of various clusters were captured. After the boundary of clusters was determined by the gray level threshold method, clusters were classified by the distance between particles and the shape and position of clusters. In addition, the process of clusters forming and breaking up was described, and the sizes of clusters were also obtained. With the Minimum Quadric Difference (MQD) cross-correlation algorithm suitable for high-density particles, the axial velocities of the particles were obtained in the dilute phase section. The features of particle motion were revealed by investigating statistically the magnitude and distribution of particle axial velocity in the radial direction. At most radial cross-sections, there exists a parabola-shaped distribution of upward axial velocity of particles, namely, the magnitude of axial velocity in the core region is higher than that near the wall region of the riser.     

EXPERIMENTAL STUDY ON VELOCITY PROFILE OF SUBMERGED ABRASIVE SUSPENSION JET FLOW

1. INTRODUCTIONAbrasive Water Jet (AWJ), has been developed the into a remarkable and extensively used cutting technology in last two decades. In recent years, the polymer PAM has generally been applied to jetting fluid to further increase the abrasive ve…     

PIV MEASUREMENT OF THE GAS-SOLID FLOW PATTERN IN A CFB RISER

Particle Imaging Velocimetry (PIV) is a valuable measuring tool for studying multiphase flows, such as liquid-gas and gas-solid flow. It can be used to carry out many hydrodynamic studies, in particular, to determine accurately the gas-solid flow structure in CFB (Circulating Fluidized Beds). In this paper, the technique characteristics was described in applying the PIV to measure the gas-solid flow in circulating fluidized beds. A primary experiment was completed on a CFB unit with the PIV, yielding the velocity vector fields of high-density particles for different gas-solid superficial velocities and solid recycle rates. Velocities of the transported particles were calculated with cross-correlation method. The major factors influencing the successful measurement of particle velocity with the PIV technique were also described.     

采用乳化空气泡做示踪粒子的PIV测速技术

本文介绍一种适用于水洞力学实验的采用乳化空气泡作为示踪粒子的ＰＩＶ测速技术。选用乳化空气泡做ＰＩＶ测速示踪粒子，取代了通常采用的固体颗粒，由两台ＹＡＧ大功率脉冲式激光光源组合系统做为ＰＩＶ底片记录的双脉冲曝光光源。乳化空气泡的最大优点是对实验水洞或水槽无污染，且产生方便、经济，又可以形成高质量的杨氏条纹图像。这一技术能够使得ＰＩＶ测速技术在水洞力学应用测量中真正达到实用。     

高浓度固液两相流的运动特性研究

利用固体颗粒运动的动理论，通过改变颗粒浓度可以考察非粘性颗粒在水流中运动的典型微观和宏观运动特性。本文分别对微观的颗粒速度分布函数变化和由此衍生的诸如颗粒平均速度、颗粒脉动速度和单位体积颗粒数垂线分布等宏观变量的变化进了系统比较。研究结果表明：动理论能够比传统理论获得理详细的微观和宏观信息，也更适合研究高浓度固液两相流运动特性，颗粒运动微观和宏观特性在颗粒浓度超过一定阈值后会发生本质的变化，但临界颗粒浓度值（阈值）在不同的计算和实验条件下会有一定的差别。     

固液两相流中固体颗粒的垂直分选机理

在结构两相流的总体框架内，基于对单个固相颗粒受力的分析和对多颗粒条件下颗粒之间的相互作用，本文对液体流动特性进行了简化，采用固体颗粒在水流中运动的垂线分选模型，对各种颗粒浓度条件下的垂直分选特征进行了讨论。结果表明：随着颗粒浓度的增加，颗粒的分选过程加快，颗粒向上聚集的倾向加强，分选的结果会形成明显地在垂直方向上显示出反粒序分布。当颗粒体积浓度超过0．3以后，粗颗粒较细颗粒具有更大的向上聚集的倾向；当颗粒浓度接近极限浓度时，会出现颗粒分选速度的反常变化，说明分选模型在这种情况下失效。文中还通过常见的三种液相速度分布，分析了不同速度分布剖面对分选结果可能产生的影响。     

边抛疏浚浮泥对河口地区航道淤积的影响

概述河口海岸地区航道附近浮泥存在成因及研究现状 ,将浮泥作为宾汉体 ,根据双层流模型的运动基本方程 ,推导出一维定常状态下浮泥运动速度与浮泥厚度、上层水流运动速度、底面坡度、浮泥密度、浮泥脱水速度、浮泥上层水体悬沙浓度、悬沙沉降速度、水深之间的关系及非定常状态一维浮泥运动简化方程。并对长江口北槽下段某处航槽边抛疏浚弃土中浮泥在不同水流作用下的运动进行分析计算     

高浓度固液混合流的湍流模型

建立了高浓度固液混合流的湍流模型，分析了混合流的应力（包括颗粒碰撞应力、粘性应力、湍流应力及Ｃｏｕｌｏｍｂｉｃ摩擦应力）。根据高浓度混合流中颗粒的受力，得出了颗粒运动的力平衡方程。由于引入颗粒碰撞应力和Ｃｏｕｌｏｍｂｉｃ摩擦应力，本模型较其它模型更适合具有高浓度和大颗粒的流场。利用本模型模拟的高浓度含沙水流在水平管道中的流动特性，其数值结果与前人所做的实验结果较一致。     

Effects of Bed Load Movement on Mean Flow Characteristics in Mobile Gravel Beds

The effects of bed-load movement on mean flow characteristics were experimentally investigated using particle image velocimetry (PIV). The gravel beds associated with open-channel flow are hydraulically rough, and two types of grain with different median diameters were used. The flow field and bed load motion images were simultaneously obtained via the particular experimental setup. The mass of sediment particles instantaneously moving on the bed, i.e., the sand-wave, was observed in the experiment. It was found that the sand-waves have an average friction angle of 11.2° and heights ranging from 2.2 d ₅₀ to 3.8 d ₅₀. The mean velocity profiles on the mobile bed can also be represented with logarithmic distribution with deviations occurred in the near wall region. Based on the Schultz–Grunow formula, a modified equation is developed in this study to better express the flow resistance factor in terms of the Reynolds number and the ratio of flow depth to roughness height.     

ANALYSIS OF BASSET FORCE OF PARTICLE MOTION IN TURBULENT FLOWS WITH SPECTRAL METHOD

1 .　ＩＮＴＲＯＤＵＣＴＩＯＮＷｉｔｈｔｈｅｗｉｄｅａｖａｉｌａｂｉｌｉｔｙｏｆｃｏｍｐｕｔａｔｉｏｎａｌｔｅ ｃｈｏｌｏｇｙ ,ｔｈｅｎｕｍｅｒｉｃａｌＬａｇｒａｎｇｉａｎｃｏｍｐｕｔａｔｉｏｎｆｏｒｆｌｏｗｓｉｎｖｏｌｖｉｎｇｄｉｓｐｅｒｓｅｄｓｏｌｉｄｐａｒｔｉｃｌｅｓｏｒａｉｒｂｕｂｂｌｅｈａｓｉｎｃｒｅａｓｅｄｄｒａｍａｔｉｃａｌｌｙｉｎｒｅｃｅｎｔｙｅａｒｓ .ＡｌｌｏｆｔｈｅｓｅｃｏｍｐｕｔａｔｉｏｎｓｕｓｕａｌｌｙｓｔａｒｔｅｄｗｉｔｈＬａｇｒａｎｇｉａｎｅｑｕａｔｉｏｎｏｆ ｐａｒｔ…     

论黄河干支流悬移质粒径与含沙量关系

黄河干支流资料表明，河流中悬移质泥沙粗细的变化既有随着含沙量的增加而变粗的，也有随着含沙量的增加而变细的。本文分析了黄河干支流泥沙粒径与含沙量关系的不同资料，提出了较大含沙量情况下泥沙粒径与含沙量的统计关系，解析和讨论了所推导出的悬移质泥沙粒径与含沙量的关系。     

Two-phase velocity measurement in a particle-laden jet

A horizontally discharging jet laden with solid sediment particles is investigated experimentally. The submerged jet discharges water with an initially horizontal direction into stagnant water of the same density but the presence of sediment particles produces jet effluent having a combined density greater than that of the ambient water. A modified particle-imaging velocimetry (PIV) technique is applied to estimate the velocity fields of the solid particle phase and the jet fluid liquid phase. Phase separation is achieved optically between the scattered light signals from the particles and the laser-induced fluorescence signal from the jet fluid dozed with a fluorescent dye. It is found that initial sediment concentrations below 0.1% volume fraction do not cause significant changes to the global properties of the jet flow. In jets of higher initial sediment concentrations, settling of sand particles are observed to drag the jet to spread with a downward-bending mean trajectory. Intensive particle–flow interaction is also observed in jets of high sediment concentrations.