介尺度自由面动态变形与表面内能失稳耦合的热-溶质毛细对流振荡机理研究

The research on Marangoni convection instability under microgravity environment has been included in the guideline of experimental projects for China Manned Space Station while the theoretical knowledge on thermosolutal capillary convection (TSCC) for people is neither systematic nor deep. In this project, the effect mechanism of concentration or temperature gradient on the characteristics of interface and the three-dimensional evolution of flow structure will be investigated experimentally by the high speed camera, high resolution thermal imager and self-developed software package for interface image recognition. The model for TSCC is established by considering the surface internal energy variation coupling with dynamic deformation of free surface via the improved interface energy conservation equation with the mass conservation level set function, and the dynamic response law of free surface, transition process, and oscillatory mechanism for the TSCC in floating zone will be studied numerically. Through the study on the instability of TSCC under the coupling effect of surface internal energy disturbance and dynamic free surface deformation, the flow structure characteristic, interfacial phenomenon, and instability mechanism of Marangoni convection can be illustrated comprehensively, and the effect law of oscillatory TSCC on the impurities and doping segregation in crystal will be exposed. The project aims at establishing the numerical simulation method, simulation platform, and experiment technology for the oscillatory TSCC, meanwhile, the theoretical foundation for the microgravity fluid physics and material preparation on the manned space station under the extreme environment can be provided.

微重力环境下Marangoni对流不稳定性研究已列入我国载人空间站实验项目指南，但目前对振荡热-溶质毛细对流的认识既不系统也不深入。本项目利用高速摄像仪、高分辨率热成像仪和自主开发的界面影像识别程序包实验研究浓度/温度梯度对界面特性的影响机制及流动结构的三维演化，采用改进的界面能量守恒方程，结合质量完全守恒水平集法，建立表面内能变化与动态自由面变形耦合的热-溶质毛细对流模型，数值研究浮区热-溶质毛细对流自由面动态响应规律、转涙过程和振荡机理。通过对表面内能失稳与自由面动态变形耦合作用的热-溶质毛细对流不稳定性研究，全面阐明Marangoni对流流动结构特征、界面现象及失稳机制，揭示振荡热-溶质毛细对流对晶体中杂质及掺杂偏析的作用规律。项目旨在建立振荡热-溶质毛细对流数值模拟方法、模拟软件平台与实验技术，为极端环境下载人空间站微重力流体物理及空间材料制备提供基础理论依据。

本项目利用高速摄像仪、高分辨率热成像仪和自主开发的界面影像识别程序包实验研究热-溶质毛细对流界面流特性及流动结构的三维演化，采用改进的界面能量守恒方程，结合质量完全守恒水平集法，建立表面内能变化与动态自由面变形耦合的热-溶质毛细对流模型，数值研究浮区热-溶质毛细对流自由面动态响应规律、转涙过程和振荡机理。研究表明：重力场倾角引发的表面内能失稳导致热毛细对流涡核畸变，胞元流沿径向的伸展受到抑制。随着表面内能失稳的加剧，胞元流涡核萎缩至液桥中间高位置，不同高度处的横/纵向速度峰值明显减小。由于胞元流涡心向自由表面靠近，液桥中心纵向体回流区域被扩大，界面流横/纵向速度梯度显著提升。表面内能失稳导致热角区临界温差升高，流动稳定性得到提升，振荡流发启后角区温度失稳呈现脉动特性。表面内能失稳导致振荡热毛细对流振荡周期增加，左右胞元流涡核位于热角和冷角近自由界面处。表面内能失稳导致近地侧界面流速度大于远地侧，并且沿界面高度方向呈现“∑”型分布。由于界面流速度的提升显著加速了热角区回流的补充，进而抑制了热角区振荡的发起。虽然表面内能失稳造成溶质毛细对流Bond数轴向分量（Bo'）在较小范围内变化（Bo'=1→0.98），但其对溶质Marangoni数（Mac）有显著地影响。在溶质毛细对流的发启阶段，Mac的衰减速率随Bo'数的增加而减小；在溶质毛细对流的发展阶段，Mac的衰减速率呈现相反的变化规律。项目旨在建立振荡热-溶质毛细对流数值模拟方法与实验技术，为揭示振荡热-溶质毛细对流对晶体中杂质及掺杂偏析的作用规律提供基础理论依据。