机械蝴蝶模型悬停飞行的流动显示实验

为了探索蝴蝶独特的外形及运动模式下蕴含的流动机理，与以往只考虑翅膀气动影响的拍动翼实验不同，我们开发了一种同时考虑身体及翅膀的机械系统用以模拟蝴蝶的悬停飞行，并采用染色液流动显示的方法对升力的主要来源——前缘涡进行了细致的观测。结果显示，在蝴蝶飞行的上下拍动过程中均有前缘涡产生，且不是以往观测到的螺旋或锥状结构，而是近似等直径的柱状联通形式，其明显特征为：在拍动加速阶段存在明显的展向流动，而在减速阶段则会出现破裂；另外，蝴蝶看似杂乱无章的运动实际上是一种自适应控制的结果，有助于提高升力。

Flow visualization of butterfly hovering fly via a mechanical model

In order to explore the aerodynamic theory involved in butterflies＇ unique morphology and kinematics, we developed a mechanical system considering the effect of both wings and body, differing from the previous experiments focusing only on flapping wings, to imitate a hovering butterfly. An experiment of dye flow visualization was carried out to reveal the structure of leading edge vortex （LEV）, which was the principle source of high lift. The results show that, LEVs presenting during both downstroke and upstroke are not conical or spiral as observed in previous experiments, but continuous across the body in form of column with approximately constant diameter, which are characterized by： obvious spanwise flow existing in the acceleration stage of wing flapping; and vortex breakdown during the deceleration phase . In addition, the fluttering of butterflies seems not a random, erratic wandering, but a kind of adaptive control flying which is beneficial for enhancing lift.