蜻蜓非对称扑动时的气动特性

Aerodynamic characteristics of dragonfly in asymmetric flapping

蜻蜓等昆虫作为飞行领域的佼佼者具有优异的机动性能,然而基于仿生学研制的微型扑翼飞行器在机动性能方面却远不如昆虫。为研究昆虫机动飞行时的气动特性,采用有限体积法(FVM)对蜻蜓左右两侧翅膀非对称扑动时的三维气动力及力矩进行了数值计算,并对不同扑动幅值下蜻蜓的整体气动性能以及每一个翅膀的气动性能、压力分布及流场结构进行了系统分析。结果表明:仅需增加某侧两翅的扑动幅值即可实现向另一侧的机动飞行;相比后翅,扑动幅值对前翅的升推力、滚转及偏航力矩影响较大,而对侧向力的影响较小;扑动幅值对翅膀的瞬时阻力、侧向力、偏航及俯仰力矩在整个扑动周期内均产生了明显影响,而对瞬时升力和滚转力矩的影响则集中在下扑阶段;扑动幅值改变了翅膀前缘涡、尾涡的强度及上下表面的压力差,在下扑阶段,翅膀和蜻蜓对称面有个相对倾角,气动合力产生了较大的侧向力,而上扑阶段,翅膀几乎垂直对称面,产生的侧向力较小。以上结果对于仿生扑翼飞行器的控制及气动设计具有一定指导意义。

Insects including dragonfly with powerful maneuvering performance are accounted as the best experts in aviation.However,ornithopters inspired by insects have much poorer maneuverability than insects.To find out the maneuvering aerodynamics of insects,a numerical study of the 3 Daerodynamic forces and moments of a dragonfly in asymmetric flapping is carried out using the Finite Volume Method（FVM）.The total aerodynamics of the dragonfly,aerodynamics of each wing,pressure distributions and vorticity are analyzed at different flapping amplitude.The results indicate that maneuvering flight to one side can be achieved by increasing the flapping amplitude of the two wings on the other side.Compared with the hindwing,the flapping amplitude has greater effect on the lift,thrust,roll and yaw moments of the forewing,and smaller effect on the lateral force.The instantaneous drag,lateral force,yaw and pitch moments are influenced by the flapping amplitude during the whole flapping cycle,and the flapping amplitude affects the instantaneous lift and roll moment obviously in downstroke.The flapping amplitude changes the leading edge vortex,trailing vortex and the pressure difference between the upper and lower surfaces.In down-stroke,there is a slant angle between the wings and the symmetric plane of the dragonfly to lead to greater lateral force,and in up-stroke,the wings are almost vertical to the symmetric plane,which means the generation of smaller lateral force.These results can offer some guidance for attitude control and aerodynamic design of ornithopters.