先进直升机旋翼悬停状态气动性能计算

Prediction on Aerodynamic Performance of Advanced Helicopter Rotor in Hover

为更好地模拟先进直升机旋翼流场,同时准确计算其悬停状态的气动性能,建立了一套基于Navier-Stokes/Euler方程的混合CFD方法。该方法的求解域由两部分组成:一是围绕旋翼桨叶周围的黏性区域,采用可压缩Navier-Stokes方程来模拟旋翼附近的黏性流动和近场尾涡的捕捉;二是离桨叶较远、黏性可以忽略的远场区域,用Euler方程来描述其流动。在该方法中,将三阶逆风格式(MUSCL)与通量差分分裂方法相结合,无需添加人工黏性,因而可有效地减少旋翼尾迹数值耗散。为便于流场分区求解以及周期性边界条件的实施,采用了嵌套网格方法,并给出旋翼网格与背景网格交界面的信息传递方式。应用所建立的计算方法,首先对二维翼型、三维M6机翼的流场进行了数值模拟,以验证计算方法;然后,着重计算了有实验结果可供对比的具有先进气动外形的HELISHAPE 7A模型旋翼和UH-60A直升机旋翼,通过计算得到旋翼表面压力分布、桨叶展向拉力系数分布、桨叶表面细节流动以及气动性能等,进一步验证了该方法的有效性。

In order to simulate the flow field and calculate the aerodynamic performance of advanced helicopter rotor in hover with high accuracy, a hybrid CFD method based on the Navier-Stokes/Euler equations has been developed. The flow solver has two modules： 1） a compressible Wavier-Stokes analysis near the viscous region of the blade for modeling the viscous flow and near wake; 2） an Euler flow analysis for modeling the inviscid flow regions far away from the rotor. For the solution of Naiver-Stokes/Euler equations, the combination of the third-order upwind scheme （MUSCL） and flux-difference splitting scheme without adding artificial viscosity has been employed, which can reduce the false dissipation of the rotor wake vortieity effectively. The methodology of embedded grids is also adopted to solve the flow field separately and implement the periodic boundary conditions, and a method aimed at passing information among rotor grids and background grids has been given. With the developed method, the flow fields of a 2D airfoil and the 3D M6 wing are firstly simulated and the calculated results are compared with available experimental data for the purpose of validation. Secondly, the flow fields of a four-bladed HELISHAPE 7A rotor and a four bladed UH-60A rotor with advanced aerodynamic shapes are emphatically calculated. The calculated results including pressure distributions, sectional thrust loading of the rotors, details of the flow field on blade surface and the aerodynamic performance, etc. are compared with available experimental data, which further demonstrate the validity of this method.