期刊
ROYAL SOCIETY OPEN SCIENCE
卷 8, 期 8, 页码 -出版社
ROYAL SOC
DOI: 10.1098/rsos.202172
关键词
butterfly flight; wing-pitch motion; induced flow; wake-capture effect; forward propulsion
资金
- National Taiwan University [NTU-CC-109L893301]
- Taiwan Ministry of Science and Technology [MOST 109-2221-E-002-201-MY2]
Butterflies use a small amplitude of wing-pitch motion for flight to enhance wake-capture effect and forward propulsion. When the amplitude of wing-pitch motion exceeds 45 degrees, butterflies lose part of their forward propulsion due to the weakening of the wake-capture effect.
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 degrees, 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.
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