Beneficial wake-capture effect for forward propulsion with a restrained wing-pitch motion of a butterfly. Issue 8 (25th August 2021)

• Record Type: Journal Article
• Authors: Lin, You-Jun; Chang, Sheng-Kai; Lai, Yu-Hsiang; Yang, Jing-Tang
• Is Part Of: Royal Society open science. Volume 8:Issue 8(2021)
• Publication Date: 2021-08-25
• Subjects: butterfly flight -- wing-pitch motion -- induced flow -- wake-capture effect -- forward propulsion; Science -- Periodicals; 500
• DOI: 10.1098/rsos.202172
• Languages: English
• ISSNs: 2054-5703

Abstract

Abstract : 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.