基于非定常RANS方程的刚性旋翼流场分析

为了掌握刚性直升机旋翼在高速飞行条件下的关键气动特性，本文通过求解三维非定常雷诺平均N-S(Reynolds-averaged Navier-Stokes, RANS)方程并基于多块结构化网格有限体积方法(Finite volume method, FVM)对直升机旋翼悬停及前飞状态的复杂绕流流场进行了数值模拟，讨论了动态流动分离、展向流动影响及反流等复杂气动特性的影响。分析了旋翼总距对气动载荷的影响及后行阶段的非定常反流效应，并分别揭示了该旋翼在悬停和大速度前飞状态下显著不同的气动力规律。数值计算表明，悬停状态该旋翼拉力值随总距线性增大，而在大前进比(Advancing ratio, AR)飞行时，其后行侧桨叶根部反流导致截面非常规压力分布，拉力主要由前行侧桨叶提供。数值预测结果与风洞试验结果的比较显示了良好的一致性。

Analysis on Flow-Field Around Helicopter Rigid Rotor Blades Based on Unsteady RANS Equations

For investigating the aerodynamic characteristics of rigid helicopter rotor under high speed flight speeds, the complex flow field around helicopter rotors are numerically simulated by solving the three-dimensional unsteady Reynolds-averaged Navier-Stokes (RANS) equations based on multi-block structured finite volume method (FVM). Here both hovering and forward flight conditions are considered. In the research, the effects of dynamic flow separation, local spanwise /radial flow and relevant factors are emphasized. On one hand, we focus on the influence of collective pitch of rotors on aerodynamic loadings as well as unsteady reversed flow of rotor blades during the withdrawal stage; On the other hand, distinctive laws of aerodynamic forces on blades under both hovering and forward flight are revealed. Numerical results show that, the lift over a rotor increases linearly with its collective pitch. However, during a forward flight with large advancing ratio(AR), reversed flow will appear at the blade root area in their withdrawal stages, and these produce totally different pressure distribution compared with conventional ones, which causes the lift mainly coming from the advancing blades. The numerically results show satisfactory agreement with the data from wind tunnel experiments.