倾转旋翼典型飞行状态气动特性的CFD分析

针对倾转旋翼特有的悬停、巡航、过渡3种飞行模式,基于CFD方法分别对倾转旋翼的上述3种典型飞行状态进行了数值模拟.首先,基于运动嵌套网格思想建立了适合倾转旋翼运动模拟的多层运动嵌套网格系统.然后,基于RANS(Reynolds averaged Navier-Stokes)方程建立了适用于非定常流场分析的CFD模拟方法.为了提高整个流场的计算效率,时间推进采用高效的隐式LU-SGS(lower upper symmetric Gauss Seidel)方法,并运用SPMD(single program multiple data)并行计算模式.最后,采用所建立的网格生成方法和流场求解器,进行了不同飞行状态下的倾转旋翼气动特性数值分析,验证了建立CFD方法的有效性并得出了多种飞行状态下的气动特性.结果表明:悬停状态下倾转旋翼相对于直升机旋翼有更加明显的下洗流影响区域.巡航状态两旋翼中心间距为2.5R时,倾转旋翼之间存在明显的气动干扰.过渡状态下,倾转旋翼提供的拉力在倾转角为45°前下降较快,且在倾转角较小时,倾转旋翼桨叶表面拉力分布仍能表现出直升机旋翼的特性. 

CFD analyses of aerodynamic characteristics of tilt-rotor under typical flight conditions

Considering three flights (hover/cruise/transitional mode) of tilt-rotor, numerical simulations on the aerodynamic characteristics of tilt-rotor under different conditions were conducted respectively. Firstly, a multi-layer moving embedded grid method was established. Secondly, the unsteady RANS ( Reynolds averaged Navier-Stokes) equations were taken to simulate the unsteady characteristics of the flowfield around tilt-rotor. In order to improve the computational efficiency, the implicit LU-SGS (lower upper symmetric Gauss Seidel) method and the SPMD (single program multiple data) mode of parallel computing were employed. Finally, based on the grid method generation and flow solver, the aerodynamic characteristics of tilt-rotor under different flight conditions were numerically analysed, proving that the method presented is effective to simulate the aerodynamic characteristics of tilt-rotor. Result shows that, in hover mode, the downwash of the tilt-rotor is more obvious than the helicopter rotor. The aerodynamic interference between the tilt-rotor is apparent when the distance of the tilt-rotor shafts is 2.5R in cruise mode. In the conversion mode, the thrust decreases rapidly before the 45° tilting angle, and the thrust distribution on surface of tilt-rotor blade is similar to the helicopter rotor.