共轴反桨涵道式推进单元地面效应气动性能

为了研究共轴反桨涵道式推进单元近地面悬停时的气动特性,通过气动性能测试分别研究了转速、桨盘间距和离地距离对推进单元的气动影响。同时,通过CFD数值仿真分析了其速度场和压力场分布,分析了共轴反桨涵道式推进单元地面效应的流场特性。结果表明,当涵道扩散口到地面的距离小于两倍桨盘半径时,地面效应开始起作用;当离地距离小于一倍桨盘半径时,地效非常显著,品质因子(FM)最高提升了约30%。随着离地距离的减小,涵道拉力随之降低,这是由于入流速度的降低导致涵道唇口处的压力峰值下降。桨盘间距对地面效应影响不大。涵道以及螺旋桨的拉力、反扭矩与螺旋桨转速的平方近似成正比。 

Aerodynamic performance of shrouded coaxial anti-rotating rotor propulsion unit with ground effect

In order to study the aerodynamic characteristics of shrouded coaxial rotor propulsion unit hovering near ground, experimental measurements were conducted to investigate the effects of rotational speed, rotor spacing and shroud-diffuser-height from ground. CFD simulations were performed to analyze the velocity field and pressure field distribution around propulsion unit, and the flow-field characteristic of ground effect for shrouded coaxial rotor propulsion unit was studied. Results showed that, when the distance from shroud diffuser to ground was less than two rotor radii, the ground effect began to work; when the distance was less than one rotor radius, the ground effect was very significant, and figure of merit (FM) increased by about 30% at most. As the distance decreased, the shroud thrust decreased due to the declining inflow velocity leading to the decrease of the peak pressure at the shroud lip. The rotor spacing had little effect on ground effect. The thrust and counter-torque of shroud and rotors were approximately proportional to the square of rotor speed.