微重力界面流动环状流结构及流体波研究

Research on instabilities of annular flows and hydrodynamic waves in interfacial convections in microgravity has become an important research direction in microgravity fluid dynamics. Annular flow is a simplified model for surface-tension driven convections in the Cz crystal growth. We will use theory analysis, numerical simulation and experimental method to investigate the structure of annular flows, the flow instability and the propogation of hydrodynamic waves. Pressure field will be solved using the pressure wave equation method, stability analysis will be performed using a three-dimensional stability analysis program based on the full spectral method, hydrodynamic wave structure and wave velocity will be measured using a particle tracking analysis. The effects of aspect ratio, volume ratio and Prandtl number on the critical Reynolds number, instability mode and frequency will be studied. The annular flows in interfacial convections will be constructed by setting a temperature difference between a cylindrical vessel and a plane disk. By adjusting the container chassis height, the aspect ratio and volume ratio can be changed. Through the investigation of interfacial flow structures, breakdown of annular flows and the propagation of hydrodynamic waves, we can understand the effect of interfacial flows with hydrostatic deformation and their oscillations on the solidification interfacial morphology and the distribution of impurities and dopings, and the structure characteristics of flow boundary layers and the instability mechanisms. All these investigations will provide theoretical foundation for microgravity fluid managements, hydrodynamic-wave applications and materials processing.

微重力环境下界面流动环状流失稳及流体波现象的研究成为微重力流体力学的重要研究方向。环状流是对提拉法晶体生长中界面张力驱动对流的一种简化模型。本项目将利用理论分析、数值模拟和实验手段对界面流动环状流结构、流动失稳及流体波传播机制进行研究，采用压力波方程方法求解压力，利用三维完全谱方法稳定性分析程序对环状流失稳进行分析,利用粒子示踪方法测量流体波结构及波速，揭示长径比、体积比及Pr数对临界失稳Reynolds数、失稳模态及频率的影响。界面流动环状流通过设定圆柱状容器和圆盘之间温度差产生，调整容器底盘高度可以改变环状流的长径比及体积比。通过对界面张力驱动对流结构、环状流破碎及流体波传播的研究,可以掌握变形界面流动及其振荡对晶体凝固界面形态以及晶体中杂质及掺杂分布的影响, 可以理解界面流动边界层的结构特征及流动失稳机制，并为微重力流体管理、流体波应用及材料制备提供理论基础。

微重力环境下界面流动环状流失稳及流体波现象的研究成为了微重力流体力学的重要研究方向。环状流是对浮区法及提拉法晶体生长中界面张力驱动对流的一种简化模型。项目利用理论分析、数值模拟和实验手段对界面流动环状流结构、流动失稳及流体波传播机制进行了研究，采用压力波方程方法求解压力，利用三维完全谱方法稳定性分析程序对环状流进行失稳分析，揭示了长径比、体积比及Pr数对临界失稳Reynolds数、失稳模态及频率的影响。. 利用线性稳定性分析方法研究了反向旋转圆盘之间热毛细流动的稳定性问题。对于小Pr数液体(Pr<=0.01)，圆盘旋转使得最不稳定扰动主要为三维振荡模态。但存在一个旋转速度，其对应的扰动为三维静止模态。能量分析结果表明,扰动能量包括粘性耗散、表面张力做功以及扰动流和基本流的相互作用。对于小Pr数液体(Pr<=0.01)，扰动能量主要来自于扰动和基本流的相互作用，表明流体失稳是动力学失稳。当圆盘低速旋转时，扰动和基本流在周向的作用项变为负 (ReΩ = 50)，说明低速旋转可以使得热毛细对流更稳定。. 对外壁加热的环形液池热毛细对流进行了线性稳定性分析。采用Chebyshev配点法对Pr=6.84,内外径之比为0.5,深宽比A范围为0.25 - 1.4的数值结果进行分析，发现流动的临界状态均为振荡形式,并且随着A增大,临界雷诺数减小,相应的临界波数与振荡频率也呈减小趋势。能量分析结果表明,小扰动与基本流相互作用项较小,表面张力在径向做功与周向做功对小扰动的动能变化起主导作用.观察三者与液池深宽比的关系,发现A = 0.8时,表面张力在径向做功项达到极小值,周向做功项以及小扰动与基本流相互作用项达到极大值。. 通过对界面张力驱动对流结构、环状流破碎及流体波传播的研究,掌握了变形界面流动及其振荡对晶体凝固界面形态以及晶体中杂质及掺杂分布的影响, 理解了界面流动边界层的结构特征及流动失稳机制。理论分析得到的结果为我国空间站微重力流体环状流实验的参数选择提供了参考依据。