刚毛翼拍合过程中复合运动对升力的影响

Investigation of the effect of complex motion during clap-flingon the lift performance of bristled wings

为揭示拍合过程中拍动和俯仰运动重叠对刚毛翼升力的影响,基于重叠网格方法建立了刚毛翼的计算流体动力学模型,分析了刚毛翼悬飞时的黏性效应,在此基础上研究了拍动-俯仰重叠率对刚毛翼升力系数的影响规律及机制。研究结果表明:随着基于弦长的雷诺数由10逐渐增加至80,刚毛间隙泄漏明显增强,刚毛翼内外侧压差和刚毛间隙泄漏率与雷诺数之比不断减小,导致压力和剪切力对升力系数的贡献不断减小,升力系数不断降低;通过采用较高的拍动-俯仰重叠率,可使拍合过程中的流体泄漏方向与刚毛运动方向相反,在合拢阶段形成明显的竖直向上剪切力合力,而在打开阶段形成明显的竖直向上压差,从而将合拢和打开阶段的负升力峰值转变为正升力峰值,有效提高刚毛翼的平均升力系数。

Bristled wing is a prospective approach to further miniaturization of aircraft.Clap-fling with translation-rotation overlap is often used by bristled-wing insects during hovering.To understand the effect of translation-rotation overlap on lift performance,Computational Fluid Dynamics(CFD)model of a pair of bristled wings was developed using the overset mesh method.The viscous effect of bristled wings during hovering was analyzed,and the effect of translation-rotation overlap percentage on lift coefficient was studied.The results indicate that:1)as the chord length-based Reynolds number increases from 10 to 80,the bristle gap leakage increases,and the pressure difference between both sides of the wing and the leakage rate to Reynolds number ratio decrease,resulting in decreasing pressure and shear contribution to lift,and a decreasing lift coefficient;2)by using high translation-rotation overlap percentage,the fluid leaks through the bristle gap in an opposite direction to the bristle motion,forming upward resultant shear force during clap and upward resultant pressure force during fling,such that the negative lift peaks during clap and fling can be converted into positive lift peaks and the average lift coefficient can be significantly increased.