旋翼尾流与地面干扰时地面涡现象的研究

用Ｎ－Ｓ方程对近地飞行时旋翼尾流与地面干扰时产生的地面涡现象进行了数值计算旋翼对流场的作用由分布在特定区域内的动量源项模拟结果表明，旋翼尾流撞到地面后的卷起和轴向流动的拉伸作用是形成地面涡的原因；地面边界层形成的二次分离涡向地面涡内输入（与尾流所携带的涡量）相反的涡量，而使地面涡保持平衡；地面涡的存在和运动使旋翼附近流场大大改变

INVESTIGATION OF THE GROUND VORTEX PHENOMENON DUE TO THE INTERACTION BETWEEN ROTOR''S WAKE AND THE GROUND 1)

The 3D incompressible Navier-Stokes equation was solved numerically to simulate the wake development and the ground vortex formation caused by a rotor in forward flight near the ground The characteristics of the ground vortex and the distribution of the induced velocity at rotor disc were studied and their influences by advance ratio were investigated To avoid directly simulate rotor blades with non-orthogonal curvilinear coordinates, momentum sources were added to the Navier-Stokes equation to imitate the effects of the rotor to the flow field The fine structure of the velocity field near rotors can not be revealed with this approximate method, however, the wake in far field can be predicted with a high accuracy Momentum sources were located in the blade region and the strengths of which were determined from an iterative manner of calculating the local flow field properties, the rotor geometry and the aerodynamic characteristics of the blade cross-section The finite volume method was used to discretize the incompressible Navier-Stokes equation in Cartesian coordinates Staggered meshes were employed The convective and diffusive terms were discretized with the hybrid scheme,and the coupling between the pressure and the velocity was realized with the SIMPLER scheme ADI was used to solve the algebric equations to give the final solutions The developed computer code was employed to simulate the flow field of a rotor in forward flight near the ground The 3D streamlines of the ground vortex and the 2D streamlines of the secondary vortex within the ground boundary layer were presented THree dimensional flow structure and the wake's deformation could be clearly observed Analysis revealed that: the ground vortex moves downstream towards the rotor center and its strength becomes weaker with the increase in advance ratio; the ground vortex was formed because the rotor wake impinges on the ground and then rolls up and axially stretched; the secondary separating vortex posses opposite vorticity (to the wake vorticity) to the ground vortex; the existence of the ground vortex greatly changed the velocity field near the rotor