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First published online December 28, 2007
Journal of Experimental Biology 211, 239-257 (2008)
Published by The Company of Biologists 2008
doi: 10.1242/jeb.008649

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Research Article, Biomechanics of Flight

Near- and far-field aerodynamics in insect hovering flight: an integrated computational study

Hikaru Aono¹, Fuyou Liang² and Hao Liu^3,*

¹ Graduate School of Science and Technology, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba 263-8522, Japan
² Next-generation computation research group, RIKEN, 2-1 Hirosawa, Wako-Shi, Saitama 351-0198, Japan
³ Graduate School of Engineering, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba 263-8522, Japan

^* Author for correspondence (e-mail: hliu{at}faculty.chiba-u.jp)

Accepted 12 June 2007

Summary

We present the first integrative computational fluid dynamics (CFD) study of near- and far-field aerodynamics in insect hovering flight using a biology-inspired, dynamic flight simulator. This simulator, which has been built to encompass multiple mechanisms and principles related to insect flight, is capable of `flying' an insect on the basis of realistic wing–body morphologies and kinematics. Our CFD study integrates near- and far-field wake dynamics and shows the detailed three-dimensional (3D) near- and far-field vortex flows: a horseshoe-shaped vortex is generated and wraps around the wing in the early down- and upstroke; subsequently, the horseshoe-shaped vortex grows into a doughnut-shaped vortex ring, with an intense jet-stream present in its core, forming the downwash; and eventually, the doughnut-shaped vortex rings of the wing pair break up into two circular vortex rings in the wake. The computed aerodynamic forces show reasonable agreement with experimental results in terms of both the mean force (vertical, horizontal and sideslip forces) and the time course over one stroke cycle (lift and drag forces). A large amount of lift force (approximately 62% of total lift force generated over a full wingbeat cycle) is generated during the upstroke, most likely due to the presence of intensive and stable, leading-edge vortices (LEVs) and wing tip vortices (TVs); and correspondingly, a much stronger downwash is observed compared to the downstroke. We also estimated hovering energetics based on the computed aerodynamic and inertial torques, and powers.

Key words: computational fluid dynamics (CFD), far-field flow, fruit fly, hawkmoth, hovering, leading-edge vortex (LEV), near-field flow, unsteady aerodynamics

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