微重力下周围剪切气流引入气液自由面动态变形研究

Dynamic behaviour of gas-liquid free surface in floating zone under surrounding enviroment has become an important research topic in microgravity fluid dynamics.The liquid bridge is a ideal model for the crystal growth in floating zone method. Considering the prominent problems existing in the study on the dynamics for the free surface deformation of liquid bridges, the present project will conduct deeply a research for the effect of the surrounding shear-driven gas flow on the free surface deformation of liquid bridges in floating zone.Under the conditions of a large range of volume and aspect ratios as well as different gas velocities, the free surface deformation of liquid bridges caused by shear-driven gas flow will be measured experimentally when the Bond number is larger greatly than the Capillary number.The improved level set method with high accuracy will be developed, and the study will be carried out numerically to investigate the free surface deformation caused by the shear-driven gas flow, the subcritical deformation due to stationary convection, and the supercritical deformation due to oscillatory convection.The influence of gas flow velocity, its direction, and the volume and aspect ratios on the free surface deformation of liquid bridges as well as its instability will be revealed.Through the research on the free surface deformation of liquid bridges in floating zone under surrounding environment, we can understand deeply the behavior characteristics of the gas-liquid free surface under microgravity, and the effect of surrounding environment on the solidification interfacial morphology and the distribution of impurities in the crystal growth will be known, which will provide theoretical foundation for the prediction and management of the space fluid behavior. The present project has both important scientific significance and engineering application value.

周围环境下浮区气液自由面动力学行为已成为微重力流体力学重要研究热点。液桥是浮区法晶体生长的理想模型。针对液桥自由面变形动力学研究中存在的突出问题，本项目将深入研究周围剪切气流对浮区液桥自由面变形的影响效果。大范围体积比、长径比和不同气流速度条件下，对Bond数远大于热毛细数液桥，实验测量剪切气流引起的液桥自由面变形。拟开发高精度水平集法，数值研究周围剪切气流引入的自由面动态变形、稳态热毛细对流引起的自由面次临界变形、振荡热毛细对流引起的自由面超临界变形。揭示剪切气流速度、进气方向、液桥体积比、高径比对液桥自由面变形及其不稳定性的影响。通过对周围环境下浮区液桥自由面变形研究，可以深入理解微重力下气液自由面行为特性、掌握周围环境对晶体凝固界面形态及晶体中杂质分布的影响，并为空间流体行为预测与管理提供理论基础。项目兼具重要的科学意义和工程应用价值。

液桥作为浮区法晶体生长的理想简化模型，其自由面动力学研究一直备受关注。针对液桥自由面变形动力学研究中存在的突出问题，本项目深入研究了剪切气流速度、进气方向、液桥体积比、高径比对液桥自由面变形及其不稳定性的影响。研究主要包括几个方面：（1）开发了高精度水平集法，用于俘获剪切气流作用下液桥振荡自由面，大大提高了自由面俘获数值计算的精度；（2）开发了周围剪切气流式液桥生成装置，开展了周围剪切气流引入液桥自由面动态变形实验以及液桥内流型可视化实验，获得了清晰的振荡流结构图像，实现了液桥热毛细对流可视化研究的重要突破；（3）应用本项目开发的高精度水平集法，自编了液桥自由面动态变形数值模拟软件平台；采用Fluent软件开发了基于VOF法的液桥自由面变形数值模拟平台。利用上述两个平台，开展了剪切气流作用下液桥自由面动态变形数值模拟，研究了剪切气流与热毛细对流耦合作用下液桥自由面动态变形以及液桥内流型分布，揭示了剪切气流对表面张力驱动对流自由面稳定性的影响规律，为我国空间站实验中实现气液自由面不稳定性的有效预测与控制打下了坚实的基础。本项目取得了2项有特色的液桥生成装置发明专利和3项实用新型专利。