基于非结构嵌套网格方法的旋翼地面效应数值模拟

Numerical Simulation on Flowfield of Rotor in Ground Effect Based on Unstructured Embedded Grid Method

建立了一个基于非结构嵌套网格的流场求解器,用来精确模拟复杂的旋翼近地流场,为更好地分析地面效应(IGE)对旋翼气动特性的影响提供一套计算方法。在该求解器中,控制方程采用惯性坐标系下的非定常N-S方程,空间方向上采用二阶迎风格式,并用背景网格的一个面模拟地面作用,以方便地面边界条件的处理。应用所建立的模型,首先针对有实验结果可供对比的旋翼无地面效应(OGE)流场进行了数值模拟,以验证计算方法。然后着重计算了IGE下流场中的桨尖涡空间位置和旋翼拉力增益,并对旋翼在小速度前飞状态下的近地流场及地面涡形成过程进行了模拟和分析。在此基础上,得出了一些有意义的结论。

A computational fluid dynamics （CFD） solver based on the unstructured embedded grid technique is developed aiming at simulating the flowfield of a rotor in ground effect （IGE） and analyzing the effect of the ground on rotor aerodynamic characteristics with accuracy. In this solver, the three-dimensional unsteady N-S equations are discretized by a second-order upwind finite-volume scheme and one surface of the background em- bedded mesh is used to simulate the effect of the ground. By the model developed, the rotor flowfield in the out of ground effect （OGE） condition is first simulated and the calculated results are compared with available ex- perimental data for validation. Then, the location of the blade-tip vortex and the rotor thrust increment in the IGE condition are calculated, and the flowfield characteristics and the development of the ground vortex in low-speed forward flight in the IGE condition are also simulated. Based upon the above simulation results, some meaningful conclusions are drawn.