基于高阶逆风通量差分裂格式的直升机旋翼前飞流场模拟

描述了三维雷诺平均NS方程数值模拟前飞状态旋翼非定常流场的方法和模型.在该模型中,将三阶逆风格式(MUSCL)与通量差分裂方法相结合,无需添加人工粘性,因而可有效地减少Jameson二阶中心差分有限体积法导致的旋翼尾迹数值耗散.为充分考虑旋翼尾迹对流场的影响和计入桨叶的旋转、挥舞、变距运动,发展了一种运动嵌套网格.针对嵌套网格中关键的贡献单元搜寻问题,提出了一种新的"伪贡献单元搜寻法".应用上述方法,对Caradonna模型旋翼在周期变距和挥舞运动条件下的前飞流场进行了计算,与采用Jameson二阶中心差分方法相比,计算结果更贴近实验值.并针对几种不同桨尖形状的旋翼前飞流场进行计算,表明后掠桨尖可有效减弱超临界流动.

Calculations for the flowfield of helicopter rotors in forward flight based on high-order upwind flux-difference splitting scheme

A Reynolds-average NS solver has been developed for the prediction of 3-D unsteady flow phenomena that occur on helicopter rotors in forward flight.For the solution of NS equations the combination of the third-order upwind scheme(MUSCL) and flux-difference splitting scheme without adding artificial viscosity has been employed.As a result,the method can reduce the false dissipation of the rotor wake vorticity effectively when compared to Jameson's second-order cell-centered finite volume approach.To incorporate the important effects of the rotor wake and account for the rigid blade motions in rotation,flapping and pitching,a moving embedded grids methodology has been adopted.Aiming at the key identification issue of donor elements in embedded grids,the present analysis implements a new searching scheme,the Pseudo-Searching Scheme of Donor Elements (PSSDE),for improvement purposes.As numerical examples,simulation results on surface pressure distributions are presented for a two-bladed Caradonna model rotor in forward flight at different pitching and flapping angles.Better agreements are found with measurements or other calculated results contrast with the second-order center-difference scheme.Also,unsteady lifting results,simulated for three different blade-tip planforms,are given and the benefit of swept tips in suppressing supercritical flow is demonstrated.