悬停状态共轴刚性双旋翼非定常流动干扰机理

Unsteady flow interaction mechanism of coaxial rigid rotors in hover

基于运动嵌套网格方法,建立了一套适合于悬停状态下共轴刚性双旋翼非定常干扰流场分析的计算流体力学(CFD)方法。首先,基于高效的运动嵌套网格技术,采用积分形式的可压雷诺平均Navier-Stokes(RANS)方程作为双旋翼非定常流场求解控制方程,湍流模型选用Baldwin-Lomax模型,时间推进采用双时间方法。在CFD方法的验证基础之上,对干扰过程中的桨尖涡涡核位置及强度演变规律进行了细致分析,揭示了共轴双旋翼非定常干扰流场中上、下旋翼桨尖涡与双旋翼桨叶之间的贴近干扰、碰撞现象,以及上、下旋翼桨尖涡之间的相互干扰机理。然后,进一步研究了不同总距角下的共轴旋翼系统中上、下旋翼的非定常气动特性以及影响规律。计算结果表明:上旋翼桨叶的桨尖涡会直接与下旋翼桨叶发生碰撞,导致下旋翼桨叶拉力损失;上旋翼桨叶的桨尖涡和下旋翼桨叶的桨尖涡相互干扰,改变了桨尖涡的强度和轨迹;上、下旋翼桨叶相互靠近时,上、下旋翼桨叶的拉力均会上升,之后相互远离时上、下旋翼桨叶拉力均会先下降再上升。

A computational fluid dynamics （CFD） method based on moving-embedded grid technique is established to simu- late the unsteady flow field of the coaxial rigid rotor in hover. In this solver, based on the highly-efficient moving-embedded grid technology, the simulation method is developed by solving the compressible Reynolds-averaged Navier-Stokes （RANS） equations with Baldwin-Lomax turbulence model and a dual-time method. Based upon the validation of the present OFD meth- od, during the process of blade-vortex interaction in hover, close vortex-surface interactions and impingement phenomenon have been observed~ at the same time, the interaction process among the vortexes shed from the upper blades and lower blades has been captured obviously, as a result, the evolution laws of position and strength of blade-tip vortex shed from dif- ferent blades are obtained in detail. Furthermore, the periodic unsteady characteristics and variation trend of the aerodynam- ic forces of the upper rotor and lower rotor have been analyzed. The simulation results demonstrate that the upper blade vor- tices can impinge upon the lower blade, which causes the thrust loss of lower blade; the strength and positions of the vorte- xes shed from upper blades and lower blades could change due to the interaction; the forces on both the upper and lower ro- tors increase as the blades approach, then decrease and increase again as they move away.