Unsteady Wake Characteristics of a Flapping Wing through 3D TR-PIV
Publication: Journal of Aerospace Engineering
Volume 25, Issue 4
Abstract
The unsteady wake characteristics of a butterfly-shaped wing undergoing flapping and feathering motions are studied. A 4-bar quick return mechanism is used to generate the flapping motion. To achieve considerable feathering motion, the leading edge of the wing is fixed to the flapping arm of the model, while the trailing edge of the wing is kept free to bend and deform out of weight and aerodynamic loading. The flapping frequency and wing size considered for this study cover rotational Reynolds numbers of 6,040–10,080 for a zero advance ratio. The three-dimensional (3D) (stereoscopic) time-resolved (TR) velocity field is measured to understand the dynamics of the lift and thrust generation. The conservation of momentum principle has been used to estimate the thrust force from the particle image velocimetry (PIV) results. The mean velocity profiles in the wake show the frequency dependence ejection of the trailing edge vortex, which is believed to be effectively used for thrust production and maneuvering with various sized butterflies. The unsteady lift generation mechanism is discussed with the help of the measured variation of circulation with time. The thrust estimated from the PIV indicates positive generation throughout the entire cycle of flapping. An analytical approach for lift and thrust estimation has been considered for better understanding of the expected nature and variation of these aerodynamic forces.
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Acknowledgments
The writers acknowledge partial financial support from Asian Office of Aerospace Research and Development and the Air Force Office of Scientific Research for partial support of this work. The writers would also like to acknowledge Department of Science and Technology, India, for the support for the TR-PIV system under the Fund for Improvement of Science and Technology under DST.
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Published In
Journal of Aerospace Engineering
Volume 25 • Issue 4 • October 2012
Pages: 547 - 558
Copyright
© 2012 American Society of Civil Engineers.
History
Received: Feb 1, 2011
Accepted: Dec 12, 2011
Published online: Dec 14, 2011
Published in print: Oct 1, 2012
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