Lin You-Jun, Chang Sheng-Kai, Lai Yu-Hsiang, Yang Jing-Tang
Department of Mechanical Engineering, National Taiwan University, Taipei 10617, Taiwan.
R Soc Open Sci. 2021 Aug 25;8(8):202172. doi: 10.1098/rsos.202172. eCollection 2021 Aug.
Unlike other insects, a butterfly uses a small amplitude of the wing-pitch motion for flight. From an analysis of the dynamics of real flying butterflies, we show that the restrained amplitude of the wing-pitch motion enhances the wake-capture effect so as to enhance forward propulsion. A numerical simulation refined with experimental data shows that, for a small amplitude of the wing-pitch motion, the shed vortex generated in the downstroke induces air in the wake region to flow towards the wings. This condition enables a butterfly to capture an induced flow and to acquire an additional forward propulsion, which accounts for more than 47% of the thrust generation. When the amplitude of the wing-pitch motion exceeds 45°, the flow induced by the shed vortex drifts away from the wings; it attenuates the wake-capture effect and causes the butterfly to lose a part of its forward propulsion. Our results provide one essential aerodynamic feature for a butterfly to adopt a small amplitude of the wing-pitch motion to enhance the wake-capture effect and forward propulsion. This work clarifies the variation of the flow field correlated with the wing-pitch motion, which is useful in the design of wing kinematics of a micro-aerial vehicle.
与其他昆虫不同，蝴蝶在飞行时翅膀俯仰运动的幅度较小。通过对真实飞行蝴蝶的动力学分析，我们发现翅膀俯仰运动幅度受限会增强尾流捕获效应，从而增强向前推进力。结合实验数据进行的数值模拟表明，对于较小的翅膀俯仰运动幅度，下拍过程中产生的脱落涡会引导尾流区域的空气流向翅膀。这种情况使蝴蝶能够捕获诱导气流并获得额外的向前推进力，该推进力占总推力产生的比例超过47%。当翅膀俯仰运动幅度超过45°时，脱落涡诱导的气流会从翅膀旁漂移开；这会削弱尾流捕获效应，并导致蝴蝶失去一部分向前推进力。我们的研究结果揭示了蝴蝶采用较小翅膀俯仰运动幅度以增强尾流捕获效应和向前推进力的一个重要空气动力学特征。这项工作阐明了与翅膀俯仰运动相关的流场变化，这对微型飞行器的翅膀运动学设计具有重要意义。
