中文摘要：

热毛细对流及其不稳定性是微重力流体科学研究的重要内容．对该问题的研究不仅有利于人们对微重力环境下流体行为、对流不稳定性和湍流转捩过程等基础物理现象的进一步认识，而且也将促进晶体生长、薄膜制备等空间和地面高新技术的发展．实验研究了矩形液池中浅液层在水平温度梯度作用下产生的热毛细对流及其稳定性．实验中，成功地利用PIV（particle image velocimetry）技术对1mm^2/s硅油液层内的浮力热毛细对流流场结构进行了大量观测．结果表明，液层中的流场结构经历了多种状态的转变，该过程会受到液层厚度的影响．当液层厚度较小时，比如当d：2．8mm时，随着液池两端温差的增大，液层中的流场结构会经历单胞对流到双胞对流再到多胞对流的转变，到达多胞对流状态之后，继续增大温差，对流涡胞的数量会有所减少，而当温差进一步增大到一定程度以后，整个液层转变为三维非定常流动；当液层厚度较大时，比如当d=4．5mm时，随着温差的增大，流动模式的转变主要体现在水平截面流场截面上面，当温差增大到一定程度以后，在靠近高温端的附近区域会出现具有明显三维效应的“梭形结构”，该梭形结构的尺寸随着温差的增大而增长，并在温差超过某个临界值时失去对称性，整个液层转变为三维非定常流动．

英文摘要：

The thermocapillary convection and its instability is an important problem in the mierogravity fluid science. Its study will not only improve our understanding of the fluid behavior in microgravity conditions but also benefit the space and terrestrial applications such as the crystal growth and the film preparation. This paper studies the thermocapillary convection in thin liquid layers contained in an open rectangular cavity with differently heated sidewalls. In our experiments, a rectangular cavity of l = 52 mm and w = 36 mm is used, and the silicone oil with the kinetic viscosity of 1cSt is chosen as the working fluid whose Prandtl number is 16.2 at 25℃. The particle image velocimetry （PIV） is employed to observe and measure the flow structure in the thin liquid layers. Multiple flow states are observed within the parameter range examined. It is found that the transition routes depend on the thickness of the liquid layer. For thinner layers, as △T is increased, the flow structure in the vertical section transits first from the unicellular flow to the bicellular fl0w, and then to multicellular flow with several corotating rolls embedded in the main flow. And the number of the rolls decreases as △T is increased. The flow will eventually become time dependent and three dimensional if △T is even larger. While for thicker layers, the transition route is different. As △T is increased, the topology of the flow structure in the vertical section changes little, but different flow states can be differentiated in terms of the flow structure in the horizontal section. When AT is small, the flow near y = 0 is two dimensional. As AT is increased, shuttle structures will occur, which are symmetric with respect to y = 0. But a larger △T will destroy the symmetry and turn the flow in to a 3D unsteady flow.