半浮区液桥热毛细振荡流

采用非定常、三维直接数值模拟方法研究大Pr数半浮区液桥热毛细对流从定常流向振荡流的过渡过程．文中详细描述了热毛细振荡流的起振和振荡特征，给出了液桥横截面上振荡流的流场和温度分布．在地面引力场条件下计算的结果与地面实验的结果进行比较，得出液桥水平截面上的流场和温度分布图样以一定的速度旋转，自由表面固定点处流体的环向流速正、负交替变化的一致结论．

THE OSCILLATORY THERMOCAPILLARY CONVECTION IN A FLOATING ZONE

The convection driven by buoyancy is weaken in microgravity environment. It is possible to obtain a high-quality and large-scale crystal by using floating zone method without pollution and shear from wall of the container in space. The convection driven by surface-tension gradient at the free surface, called as thermocapillary convection, will be dominant in microgravity environment. The half floating zone has been used as one of the models to study thermocapillary convection since the end of 1970s. The experiments discovered that the steady and axisymmetric thermocapillary convection becomes unsteady and asymmetric oscillatory convection if the applied temperature difference is over the critical value. The thermocapillary oscillatory convection will affect the quality of the crystal. The oscillatory mechanism of thermocapillary convection is an open and interesting problem.The transient process from steady convection to oscillatory convection in a liquid bridge of floating half zone with large Prandtl number fluid is studied by using the numerical method of unsteady and three-dimensional calculation in the present paper. The onset process of oscillation and oscillatory features are discussed in detail, and the flow fields and temperature distributions in the cross-section of liquid bridge are obtained. The calculated results for the case of one-g condition on the ground are compared with the experimental one for the same condition. Both results conclude that, the patterns of flow field and temperature field in a horizontal cross-section of liquid bridge rotate at a certain rotating velocity, however, the azimuthal velocity at a fixed point changes alternately between positive and negative values.