高超声速边界层液膜演化过程和冷却机理研究
STUDY ON HYPERSONIC BOUNDARY LAYER LIQUID FILM EVOLUTION AND COOLING MECHANISM
-
摘要: 高超声速液膜冷却技术是通过一系列狭缝或孔洞压出冷却工质, 在飞行器表面边界层形成一层低温冷却膜, 阻止高超声速气流对飞行器的气动加热. 其作为一种主动冷却方式在高超声速飞行器表面热防护有着巨大的应用潜力. 文章采用数值方法, 结合VOF模型, 研究25 km飞行高度和Ma=5气流条件下的液膜铺展情况, 并通过不同冷却工质的入射速度、角度、表面张力和黏性系数条件, 讨论了液膜在平板上的演化过程和冷却机理. 结果表明, 在气流作用下, 液膜向壁面下游发展, 液膜的存在导致边界层分离, 连续液膜会在一定位置断裂为液块, 然后进一步破碎为液滴. 入射条件和液体性质的改变, 会影响液膜沿流向的发展, 具体表现在连续液膜断裂点的位置和连续液膜的厚度. 在所设定的计算域内, 壁面热流降低了80% ~ 95%, 液膜对壁面的冷却效率随着液膜形态的变化而变化.Abstract: Hypersonic liquid film cooling technology is to press out the cooling medium through a series of slits or holes, creat a low-temperature cooling film in the boundary layer of the surface of the aircraft to prevent the aerodynamic heating of the aircraft by hypersonic airflow. As an active cooling method, it has great application potential in surface thermal protection of hypersonic vehicle. In this paper, numerical methods and VOF model are used to study the spreading of liquid film at 25 km flight altitude and Ma=5 airflow. The evolution process and cooling mechanism of liquid film on a flat plate are discussed through the incident velocity, Angle, surface tension and viscosity coefficient of different cooling medium. The results show that under the action of air flow, the liquid film develops downstream to the wall surface, the existence of the liquid film leads to the boundary layer separation, and the continuous liquid film will be broken into liquid blocks at a certain position, and then further broken into droplets. The change of incident conditions and liquid properties will affect the development of the liquid film along the flow direction, which is manifested in the position of the fracture point and the thickness of the continuous liquid film. Within the computational domain set in this paper, the wall heat flow is reduced by 80% ~ 95%, and the cooling efficiency of the liquid film on the wall varies with the the change of the liquid film morphology.