昆虫飞行的高升力机理

UNSTEADY LIFT MECHANISMS IN INSECT FLIGHT

对近年来关于昆虫产生非定常高升力的研究进行了综述和归纳.这方面的工作对生物学研究和微型飞行器等微型机械的仿生设计有重要意义.研究表明:果蝇等昆虫翅膀的拍动运动可产生很大的非定常升力,其平均值是定常值的2～3倍,足够平衡昆虫的重量,并有较大的富余用于机动飞行;产生高升力有三个因素:一是拍动开始阶段翅的快速加速运动,二是拍动中的不失速机制,三是拍动结束阶段翅的快速上仰运动.人们从能耗的角度考察了这些非定常高升力机制的正确性和可行性.当作悬停飞行的果蝇用以上机制产生平衡其重量的升力时,其比功率（支持单位身体质量所需的功率）约为 29 W/kg;生化/机械效率约为 17％.这些值与人们基于对昆虫肌肉力学特性的研究所预估的值接近.果蝇前飞时,其比功率随速度变化的曲线是一J形曲线,而不是象飞机或鸟的那样是一U形曲线;这与人们基于昆虫新陈代谢率的测量数据所推断的结果一致.对于蜻蜒等（功能上）有前、后两对翅膀的昆虫,有以下初步结果:翅的下拍主要产生升力,上挥主要产生推力;下拍时的平均升力系数可达2～3,十分大,上挥时的平均推力系数可达1～2,也很大,它们主要由非定常效应产生;前、后翅的相互干扰并未起增大升力和推力的作用,反而有一定的不利作用.

Recently, interest has been directed to small autonomous flying vehicles, largely motivated by the need for aerial reconnaissance robots inside buildings and confined spaces. In military and commercial fields, there are similar potential demands for such micro-air vehicles (MAVs). The linear dimension of the intended MAVs ranges from 10 cm to 1 cm or even smaller. At such a size, the fixed- or rotary wing aerodynamic configuration would not work because the Reynolds number (Re) of the wing is so low that enough lift and control forces could not be produced. Novel aerodynamic configuration must be sought. However, there already exist such autonomous MAVs in nature: the insects. In the design of small flying machines, it would be very helpful to understand first how these small animals fly. In this article, we review recent achievements in the field of insect flight aerodynamics. We first summarize the kinematics of the flapping motion of insects. Next we present issues related to the unsteady lift mechanisms of flapping wings of the fruit fly and similar insects. Then we discuss the lift (and thrust) and power requirements of hovering and forward flight in the fruit fly. Recent work on insects with two pairs of wings is also discussed.