为了了解微重力条件下新型分离结晶生长过程中熔体热毛细对流的基本特征,利用有限差分法进行了数值模拟,熔体深径比A取1和2,自由界面无因次宽度B分别取0.05、0.075和0.1.当熔体上表面为自由表面时,得到了分离结晶Bridgman生长过程中熔体热毛细对流的流函数和温度分布.计算结果表明:当Ma数较小时,在上下两个自由表面的表面张力的驱动下,熔体内部产生了两个流动方向相反的流胞,流动为稳态流动,随着Ma数的增加,上下自由表面速度增大,温度分布的非线性增加;当Ma数超过某一临界值后,流动将转化为非稳态流动;与熔体上表面为固壁时相比,A=1时的临界Ma数减小,而A=2时的临界Ma数增大;流动失稳的物理机制是流速的变化和阻力的变化之间存在滞后.
In order to investigate fundamental characteristics of thermocapillary convection in the detached solidification under microgravity.the finite-difference method is adopted to perform a numerical simulation for the melt of CdZnTe with the aspect ratio A=1 and 2 and the width of gap B=0.05.0.075 and 0.1.When the top surface is free surface.the distribution profiles of temperature and stream function of molten liquid can be obtained with different Marangoni numbers.The result shows that when Ma is small,there are two steady toroidal roll cells in the molten liquid counter-flows caused by the gradient of surface tension in the upper and lower free surface.With Ma increasing,the velocity on the two free surfaces and the non-linearity of temperature distribution will be improved.On the contrary,the flow is unstable when Ma exceeds the critical Ma.Compared with the top surface being solid wall,the critical Marangoni number for A=1 is lower,but for A=2 is larger.The physical mechanism of this unstable thermocapillary convection can be explained by that there is a hysteresis between the variety of the velocity and the variety of the resistance.
参考文献
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