蜻蜓滑翔时柔性褶皱前翅气动特性分析

NUMERICAL STUDY ON THE AERODYNAMIC PERFORMANCE OF THE FLEXIBLE AND CORRUGATED FOREWING OF DRAGONFLY IN GILDING FLIGHT

蜻蜓是自然界优秀的飞行家,滑翔是其常见且有效的飞行模式.蜻蜓优异的飞行能力来源于其翅膀的巧妙结构,褶皱是蜻蜓翅膀上最为显著的结构之一,不仅提高了翅膀的刚度,还改变了其气动特性,而飞行过程中柔性翅膀会产生变形是蜻蜓翅膀的另一特性.为揭示蜻蜓在滑翔时,柔性褶皱前翅的变形,探究褶皱和柔性的共同作用对其气动特性的影响,基于逆向工程,依据前人的测量数据和研究成果,通过三维建模软件建立了蜻蜓三维褶皱前翅的计算流体力学(computational fluid dynamics,CFD)模型和计算结构力学(computational structural mechanics,CSD)模型,并通过模态分析验证了此模型有足够的精度.基于CFD方法和CFD/CSD双向流固耦合计算方法分别对蜻蜓滑翔飞行时刚性和柔性褶皱前翅的气动特性进行了数值模拟,结果表明,柔性褶皱前翅受气动载荷后,翅脉和翅膜产生形变,柔性前翅上下表面压力差相较于刚性前翅减小了,从而其升力和阻力也减小了,而在大攻角时,变形后的前缘脉诱导出比刚性前翅更强的前缘涡.因此在攻角小于10?时刚性前翅的气动特性优于柔性前翅,继续增大攻角,柔性前翅的气动特性则优于刚性前翅.前翅受载后气动响应时间短,翅尖的变形最大,仅仅产生了垂直于翅膀所在平面方向上的变形,而没有发生扭转,翼根处受到应力最大,褶皱上凸部分承受蜻蜓滑翔时前翅的主要载荷.

Dragonflies are capable of carrying out dramatic flight manoeuvres,gliding flight is a common mode of flight for dragonfly,and dragonfly wings are the source of dragonflies dramatic flight manoeuvres.Unlike typical engineered airfoil,dragonfly wings are not smooth,wing cross-section are highly corrugated.It has been shown that corrugations could enhance the spanwise stiffness in the wings and influence aerodynamic performance of the dragonfly wings.Flexibility is another characteristic of the dragonfly’s wings,which is mainly manifested as the flexible deformation of the wings during the flight.To explore corrugations and flexibility effect on aerodynamic performance of the dragonfly forewings in gliding flight,a computational fluid dynamics(CFD)model and a computational structural mechanics(CSD)model of the corrugated dragonfly forewing are established based on current research,and the modal analysis verified that the model has suffcient accuracy.The corrugated rigid and flexible dragonfly forewing are acquired by using CFD method and CFD/CSD coupling method respectively.The simulation indicated that flexible and corrugated forewings is subjected to aerodynamic load,which only produces bending deformation without torsion deformation in gliding flight,and the aerodynamic response time is short.Compared with the aerodynamic performance of the rigid and corrugated forewings,the result showed that veins and cuticular membrane of flexible forewing are deformed which caused the lift coeffcient and drag coeffcient decrease,the leading edge vortex of flexible forewing is much higher than rigid forewings at large angle of attack because of deformed vein.The aerodynamic performance of rigid forewings is better below 10 degree angle of attack,and the aerodynamic performance of flexible forewings is better at large angle of attack as result.