过冷水滴形态变化的动力学机理和表面粗糙度的形成过程研究

In this project, physical mechanism and new mathematical description methods for the super cooled water droplets impacting on the surfaces and roughness formation process are studied in details to improve the prediction precision of ice accretion. Two phase coupled governing equations of incompressible droplet and compressible air are established. Considering the rigidity of water, a new interface boundary condition for the droplet-gas multiphase flow problems is derived theoretically to conduct the coupling discrete solve of the compressible air flow and the impressible water droplets flow. And the Ghost Fluid Method (GFM) is used to handle the interface boundary problem. The Level-set interface tracking method combined with local grid refinement is adopted to accurately capture the droplet boundary. Then droplet deformation, broken up, rebound and splash can be simulated accurately to improve the prediction precision of droplet impingement properties. Analytical models for surface roughness are established respectively based on different state of unfrozen water, which is help to enhance the prediction precision of surface roughness. The morphology change of droplets and dynamical roughness model are added to icing numerical simulation programme to improve the prediction precision of the scope of impact and freezing and icing shape, which can provide basic theoretical support for the high precision aircraft icing numerical simulation.

本课题以提高飞机结冰数值模拟精度为背景，主要研究过冷水滴撞击物面后的形态变化、表面粗糙度演化的物理机理和新的数学描述方法。建立不可压缩过冷水滴-可压缩空气的两相流流场动力学模型；在考虑水的不可压缩性基础上，理论推导出一个新的针对水气两相流问题的界面边界条件，并采用Ghost Fluid Method（GFM）方法处理水气边界问题；运用界面追踪方法,结合自适应网格技术加密水滴流场，精确捕捉过冷水滴-空气和过冷水滴-固壁界面，准确模拟过冷水滴撞击表面后发生的变形、破碎、反弹、飞溅现象，提高表面水滴撞击特性的预测精度。针对附着在表面的水滴形成的不同形态分别建立受环境因素制约，且随时间和空间变化的粗糙度模型和数学表述方法，提高结冰表面粗糙度的计算精度。将水滴形态动力学模型和动态粗糙度模型融入结冰数值模拟程序，提高水滴撞击范围、冻结范围、冰形的预测精度，为高精度飞机结冰数值模拟方法提供基础理论支撑。

本课题以提高飞机结冰数值模拟精度为背景，主要研究过冷水滴撞击物面后的形态变化、表面粗糙度演化的物理机理和新的结冰数值模拟方法。设计了过冷水滴发生系统，建立了过冷水滴动力学特性试验平台，采用高速摄影技术，开展了过冷水滴在运动过程中的变形和破碎试验、过冷水滴撞击表面后的飞溅试验，获得了水滴变形对阻力系数的影响规律，建立了水滴破碎的无量纲准则判据，以及水滴入射速度、入射角度和基地表面粗糙度对飞溅特性的影响规律，并在此基础上建立了过冷水滴变形、破碎与飞溅的修正模型。通过研究过冷水滴在物面的流动特性，将流动区域分为水膜、水珠和溪流三个区域，并分别建立表面粗糙度模型，修正粗糙表面的对流换热量。将水滴形态变化的动力学模型和动态粗糙度模型嵌入结冰数值模拟程序，预测翼型表面的结冰冰形，并与文献试验数据进行了对比，结果表明，本项目修正后的结冰数值模拟方法提高了水滴冻结范围和冰形的预测精度，为高精度飞机结冰数值模拟方法提供了基础理论支撑。