菱形翼布局太阳能无人机螺旋桨滑流影响研究

为了探究螺旋桨滑流对低雷诺数菱形翼布局太阳能无人机气动特性的影响，采用动量源方法（MSM）与k-k_L-ω转捩模型求解雷诺平均Navier-Stokes（RANS）方程对不同转速状态下菱形翼布局太阳能无人机的气动特性进行了准确模拟。并通过对比机翼表面流场结构与压力分布，分析了不同迎角下螺旋桨转速变化对菱形翼布局前后翼气动干扰的机理。研究表明:随着螺旋桨转速增大，小迎角下增升减阻效果明显，最大升阻比在3 000 r/min时提升了18.4%。在小迎角时，前翼气流受到抽吸作用，升力增加，后翼受螺旋桨旋转气流影响，前缘出现大范围吸力区，压差阻力减小。在大迎角时，前翼影响不变，后翼前缘下表面吸力区范围及强度均减弱，前缘负升力区消失，增升效果改善，压差阻力增加。由于在不同迎角时，升力增量的主要贡献部件不同，导致无人机纵向静稳定裕度随着转速的提升而增大。菱形翼布局太阳能无人机通过合理设置螺旋桨位置与转速，可有效利用螺旋桨滑流提升气动性能。 

Effects of propeller slipstream on diamond joined-wing configuration solar-powered UAV

In order to investigate the influence of propeller slipstream on the aerodynamic characteristics of low Reynolds number diamond joined-wing configuration solar-powered UAV with different rotational speeds. It was simulated accurately by solving the Reynolds Averaged Navier-Stokes (RANS) equation based on Momentum Source Method (MSM) and k-k_L-ω transition model. The mechanism of the propeller slipstream effects at different angles of attack and rotational speeds was analyzed by comparing the flow field structure and pressure distribution on the wing surface. The research shows that with the increase of the propeller rotational speed at low angle of attack, the propeller slipstream leads to the obvious increment of lift and decrement of drag. And the maximum lift-to-drag ratio is increased by 18.4% at 3 000 r/min. At low angle of attack, the air flow is accelerated by propeller, and it leads to increment of lift for the Frt-wing. And for the Aft-wing, the rotation of the air flow leads to decrement of pressure drag because of the emergence of low-pressure region at lower surface of leading edge. At high angle of attack, the effects of propeller to the Frt-wing are not changed. However for Aft-wing, the range and strength of low-pressure region at lower surface of leading edge decrease, which leads to the disappearance of negative lift area at leading edge as well as the notable increase of the lift and the pressure drag. Besides, since the main contribution components of lift increment are different at different angles of attack, the longitudinal static stability margin of UAV shows an enhancement with the increase of propeller rotational speed. The diamond joined-wing configuration solar-powered UAV can effectively utilize the slipstream of propeller to improve the aerodynamic performance by reasonably setting the position and speed of propeller.