旋转磁场对空间浮区内流场及浓度场的影响

采用全浮区模型数值研究了旋转磁场作用下熔区内热毛细对流流动特性,分析了磁场强度对流场及浓度场的影响。研究发现,无磁场时,熔体内杂质浓度场和流场呈现三涡胞对称振荡特征;温度场主要由扩散作用决定,呈对称分布。旋转磁场作用下,Ma数基本保持不变。当磁场强度B_0≤1 mT时,熔体内杂质浓度场和流场与无磁场时结构类似,但旋转磁场的搅拌作用使得熔体内周期性振荡提前出现,且当旋转磁场产生的洛伦兹力相对较大时,表面张力产生的三维振荡对流得到很好地抑制。B_0=5 mT时,周向波动被完全抑制,熔区内流场和浓度场呈二维轴对称分布。旋转磁场对熔体流动产生的轴向抑制作用和周向搅拌作用,都有助于熔体流动的稳定性、浓度分布以及温度分布的均匀性,从而有利于高质量晶体的生长。

Influence of Rotating Magnetic Field on the Convection and Concentration Field in Space Floating Zone

A numerical study of thermo-capillary convection in melting zone under rotating magnetic field was carried out with full floating zone model.The influence of magnetic field intensity was analyzed on flow field and impurity concentration field.The results show that in the absence of the magnetic field, the concentration field and flow field in the melt show a characteristic of three-vortex symmetric oscillations.The temperature field which is mainly determined by diffusion is distributed symmetrically.Under the action of rotating magnetic field, the number of Ma remains unchanged.When the magnetic field intensity B0≤1 mT, the impurity concentration distribution and flow structure in the melt are similar to the case without a magnetic field.Yet the stirring effect of the rotating magnetic field makes the appearance of the melt periodic oscillation in advance.When the Lorenz force is relatively strong, the three-dimensional vibration convection caused by surface tension is well restrained.At B0=5 mT, the circumferential fluctuation is completely suppressed, and both the flow field and concentration field in the melt zone show two dimensional axial symmetrical distributions.The axial inhibition effect and circumferential stirring action on melt flow caused by rotating magnetic field both contribute to the stability of melt flow, the homogeneity of concentration distribution and temperature distribution, which is conducive to the growth of high quality crystals.