利用PIV方法测量半浮区液桥热毛细对流的速度场

利用PIV法对硅油液桥热毛细对流的定常速度场进行了实时测量。为了便于测量，液桥上桥端面采取了铜环中嵌透明材料的方法，从液桥的顶部进行观测。当液桥上下桥有温差时，热毛细对流出现；本实验对于不同上下桥的温差，对液桥横剖面内的速度场分别进行了测量，研究外加温差对于流场速度分布的影响；并且在液桥中取了几个典型横截面进行测量，以期对大Pr数液桥的定常速度场有比较全面的定量测量。此外，实验结果也可作为数值模拟计算结果的验证。

Study on Flow Patterns of Oscillatory Thermocapillary Convection In Floating Half Zone by PIV

The velocity fields of oscillatory convection have been measured using the techniques of Particle Image Velocimetry (PIV) in a liquid bridge of half floating zone with small typical scales of a few millimeters for emphasizing the thermocapillary effect in comparison with the effect of buoyancy. The flow patterns of the oscillatory flow have been studied experimentally in a liquid bridge. The flow patterns in the liquid bridge are classified with mode numbers according to oscillatory flow characteristics. Results of the experiment show that the mode depends on the aspect ratio as well as the volume ratio of the liquid bridge. The experimental results are helpful for studying the structure of flow at the onset of oscillatory thermocapillary convection in a liquid bridge.

Experimental Study on Benard-Marangoni Convection by PIV and TCL

An experimental investigation of Benard-Marangoni convection has been performed in double immiscible liquid layers of rectangular configuration. The two kinds of liquid are 10cst silicon oil and FC-70 respectively. The velocity fields in the vertical cross-section are obtained by PIV. Flow patterns and/or temperature distributions on the horizontal interface are displayed by using thermal color liquid crystal (TLC), and the velocity distributions on the interface were also obtained with the help of the serial particle image of TCL. The evolution processes of convection are observed in the differential thickness ratio of two liquid layers, and the convection styles are discussed.

PIV技术的粒子图像处理方法

以图像相关理论为基础，研究粒子图像测带技术(PIV)的图像处理方法，编制出高精度的处理软件，重建计算模拟的粒子图像位移场，给出了自相关法与互相关法的积相磁与减相关的计算结果，及互相关的误差分析，分析了自相关与互相关区别，得出了互相关法是提高粒子图像测带技术精度的有效方法的结论，因此跨帧技术是PIV技术的发展方向。

利用PIV方法测量半浮区液桥热毛细对流的速度场

本文利用PIV法对硅油液桥热毛细对流的定常的速度场进行了实时测量。为了便于测量,液桥上桥端面采取了铜环中嵌透明材料的方法,从液桥的顶部进行观测。当液桥上下桥有温差时,热毛细对流出现;本实验对于不同上下桥的温差,对液桥横剖面内的速度场分别进行了测量,研究外加温差对于流场速度分布的影响;并且在液桥中取了几个典型横截面进行测量,以期对大Pr数液桥的定常速度场有比较全面的定量的量测。此外,实验结果也可做为数值模拟计算结果的验证。

The near wall velocity measurements in microchannels with different diameter particles by microPIV/PTV. 8th International symposium on PIV

In near wall measurements with microPIV/PTV, whether seeding particles can be effectively used to detect local fluid velocity is a crucial problem. This talk presents our recent measurements in microchannels [1][2]. Based on measured velocity profiles with 200nm and 50nm in pure water, we found that the measured velocity profiles are agreed with the theoretical values in the middle of channel, but large deviations between measured data and theoretical prediction appear close to wall (0.25mm

Experimental Study on the Transition Process to the Oscillatory Thermocapillary Convections in a Floating Half Zone

The transition process of the thermocapillary convection from a steady and axisymmetric mode to the oscillatory mode in a liquid bridge with a fixed aspect ratio and varied volume ratio was studied experimentally. To ensure the surface tension to play an important role in the ground-based experiment, the geometrical configuration of the liquid bridge was so designed that the associated dynamic Bond number Bd ≈ 1. The velocity fields were measured by Particle Image Velocimetry (PIV) technique to effectively distinguish the different flow modes during the transition period in the experiments. Our experiments showed that as the temperature difference increased the slender and fat bridges presented quite different features on the evolution in their flow feature: for the former the thermocapillary convection transformed from a steady and axisymmetric pattern directly into an oscillatory one; but for the latter a transition flow status, characterized by an axial asymmetric steady convection, appeared before reaching the oscillatory mode. Experimental observations agree with the results of numerical simulations and it is obvious that the volume of liquid bridge is a sensitive geometric parameter. In addition, at the initial stage of the oscillation, for the former a rotating oscillatory convection with azimuthal wave number m = 1 was observed while for the latter a pulsating oscillatory pattern with azimuthal wave number m = 2 emerged, and then with further increase of the temperature difference, the pulsating oscillatory convection with azimuthal wave number m = 2 evolved into a rotating oscillatory pattern with azimuthal wave number m = 2.

Influence of the thickness ratio of air layer to liquid layer on the onset of Benard-Marangoni convection

An experimental investigation of the onset of Benard-Marangoni convection has been performed in a liquid layer of rectangular configuration. The critical temperature difference was measured via the detections of both temperature field pattern (IR-imaging) on the free surface and fluid convection (PIV) in the liquid layer. The critical temperature difference or the critical Marangoni number was given. The experiments were performed for a fixed depth of air layer and a changeable depth of the liquid layer, and then the influence of the thickness ratio of the air layer to liquid layer on the Marangoni instability was studied.

尾缘吹气式火焰稳定器时均流场

为了对尾缘吹气式火焰稳定器的流场进行研究，在低速风洞中利用二维在线式互相关PIV系统，对新型稳定器及V型稳定器的近尾迹流动进行了测量，考察了可控横向射流气动参数及射流方向对新型稳定器流场的影响。结果表明，尾缘吹气式火焰稳定器与V型火焰稳定器的流场特性基本相似，但吹气射流扩大了回流区，增加了回流率和湍流脉动速度；同时发现，射流与来流动量比是影响新型稳定器后流场的主要气动参数。

The Optical Methods on Measuring Surface Deformation and Surface Wave in The Thermal Capillary Convection

An optical diagnostic system consisting of the Michelson interferometer with the image processor has been developed for the study of the kinetics of the thermal capillary convection. The capillary convection, surface deformation, surface wave and the velocity field in a rectangular cavity with different temperature's sidewalls have been investigated by optical interference method and PIV technique. In order to calculate the surface deformation from the interference fringe, Fourier transformation is used to grating analysis. The quantitative results of the surface deformation and surface wave have been calculated from the interference fringe pattern.

Experimental Study of Surface Deformation and Flow Pattern on Buoyant-Thermocapillary Convection

Free surface deformation is one of the most important physical phenomena in fluids with free surface. In the present paper, convection and surface deformation caused by thermocapillary effect in a rectangular cavity were investigated. In ground experiments, the convection was also affected by gravity. The cavity has a horizontal cross section of 52mm×42mm and the thikkness of the liquid layer is 4mm. Temperature difference between two sides of the liquid layer was increased gradually, and the flow in liquid layer will develop from steady to unstable convection. An optical diagnostic system consisting of a revised Michelson interferometer with image processor was developed to study fluid surface deformation in convection, and the displacements of free surface oscillation were determined. PIV technique was adopted to observe the evolution of flow pattern, and the velocity fields were obtained quantitatively. The present experiments demonstrate that surface deformation is quite distinct in buoyant-thermocapillary convection. in order to understand the mechanism of buoyant-thermocapillary convection, not only the hydrothermal wave instability but also the surface wave instability should be discussed.

振荡流作用下波状底床上流场特性的实验研究

利用U型振荡水槽和粒子图像测速仪(PIV)对三种固定波状底床上的流场进行了测量，得到一系列不同振幅条件下的瞬时速度场和涡量场.通过分析不同时段涡强度以及涡轨迹，讨论了底床形状对其附近流场的影响.实验结果分析表明，底床形状决定着整个涡量场特征及涡轨迹，从而决定着泥沙的净输移.这些结果对于探讨浅海区沙波、沙纹和沙垄等波状底床上泥沙输移的力学机制是很有意义的.