昆虫飞行的空气动力学

昆虫是最早出现、数量最多和体积最小的飞行者. 它们能悬停、跃升、急停、快速加速和转弯, 飞行技巧十分高超. 由于尺寸小, 因而翅膀的相对速度很小, 从而进行上述飞行所需的升力系数很大. 但昆虫翅膀的雷诺数又很低. 它们是如何在低雷诺数下产生高升力的, 是流体力学和生物学工作者都十分关心的问题. 近年来这一领域有了许多研究进展. 该文对这些进展进行综述, 并对今后工作提一些建议. 因2005 年前的工作已在几篇综述文章有了详细介绍, 该文主要介绍2005 年以来的工作. 首先简述昆虫翅的拍动运动及昆虫绕流的基本方程和相似参数; 然后对2005 年之前的工作做一简要回顾. 之后介绍2005 年后的进展, 依次为: 运动学观测; 前缘涡; 翅膀柔性变形及皱褶的影响; 拍动翅的尾涡结构; 翼/身、左右翅气动干扰及地面效应; 微小昆虫; 蝴蝶与蜻蜓; 机动飞行. 最后为对今后工作的建议. 

Aerodynamics of insect flight

Insects are the earliest, most numerous and smallest fliers in the world. They can hover, fly forward, climb and descend with ease while demonstrating amazing stabilities, and they can also maneuver in impressive ways like no other organisms could. Although the wing of an insect beats at high frequency, the wing's relative velocity is small owing to the small wing length. As a result, the mean lift coefficient of wing required to balance the insect weight is relatively high, about 1.5–2, much higher than that of an airplane at cruising flight. The Reynolds number of insects' wings is small, ranging from about 10 to 3 500. How the required high-lift coefficient is produced at such low Reynolds number? Researchers are very interested in this question and in recent years, significant progress has been made in the area. Works before 2005 have been discussed in detail in several review papers, and in this article, we review the advances made since 2005. We begin with an overview of the flapping kinematics and basic equations of fluid dynamics. It is followed by a summary of the works before 2005. Then we review the advances made since 2005, dealing in turn with measurement of wing motion in freely-flying insects, leading-edge vortex, effect of wing deformation and corrugation, vortex wake of flapping wings, ground effect and aerodynamic interaction between wings and body, flight of tiny insects, flight of butterfly and dragonfly, and maneuvering flight. Finally, we make remarks on the state-of-the-art of this research field and speculate its outlooks in the near future.