Level Set方法在地面效应数值模拟中的应用

Numerical investigation on ground effect by Level Set approach

利用Level Set方法隐式捕捉界面并能处理复杂的物质界面及其拓扑结构变化(如合并、交叉、破碎等)情况的优势,基于可压缩N-S方程的预处理技术,采用基于界面两侧介质黎曼关系的修正虚拟流体方法对介质边界进行处理;将只能应用于可压缩流动界面模拟的修正虚拟流体方法推广应用于不可压缩流动问题的模拟,数值模拟了气-水运动界面与近水面飞行器的相互影响规律。通过与将水面视为对称面的简化模型对比发现:利用自由运动界面模型计算的NACA6409翼型升力较小,能更准确地反映飞行器流场对水面形状的影响,其结果更为符合实际;文中还对比了翼型距水面不同高度时的结果,得到了翼型受水面影响的强弱与翼型距水面的高度成反比的结论。

Level Set Method is widely used in fluid interface investigation because of its capability to treat some complex issues such as surface topological merging and breaking.It relies on an implicit representation of interface whose equation of motion is numerically approximated using schemes built from those for hyperbolic conservation laws.It is the most potential technique for numerical simulation of the effect between the vehicle and gas-water surface.In this paper,the Level Set Method,combined with Preconditioning Method is presented in the simulation to analyze the effect between free moving surface and aircraft.The Preconditioning Method is designed for the flow consisting of incompressible regions,and overcome the shortcoming that the Ghost Fluid Method applicable only to compressible flow.Distinctions are found between the free surface model and the 'Fixed Wall' model.Conclusion can be drawn that the using of free surface model can get more reasonable numerical results in this simulation.Different aircraft’s heights over the surface are also analyzed;it is found that the influence of the surface increases as aircraft’s flight altitude decreases.