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Flexibility increases lift for passive fluttering wings

Published online by Cambridge University Press:  16 January 2015

Daniel Tam
Daniel Tam*
Affiliation:
Laboratory for Aero- and Hydrodynamics, Technische Universiteit Delft, Delft, The Netherlands
*
†Email address for correspondence: [email protected]
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Abstract

We examine experimentally the influence of flexibility on the side-to-side fluttering motion of passive wings settling under the influence of gravity. Our results demonstrate the existence of an optimal flexibility that allows flexible wings to remain airborne twice as long as their rigid counterparts of identical mass and size. Flow visualization and measurements allow us to elucidate the role of flexibility in generating increased lift and wing circulation by shedding additional vorticity at the turning point. Theoretical scalings are derived from a reduced model of the flight dynamics and yield quantitative agreement with experiments. These scalings rationalize the strong positive correlation between flexibility and flight time. Our experimental results and theoretical scalings represent an ideal system for the validation of computational approaches to model biologically inspired fluid–structure interaction problems.

JFM classification

Aerodynamics: Aerodynamics Biological Fluid Dynamics: Swimming/flying
Type
Rapids
Information
Journal of Fluid Mechanics , Volume 765 , 25 February 2015 , R2
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Copyright
© 2015 Cambridge University Press 

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Tam supplementary movie

Side to side movies of flexible fluttering wings falling under the influence of gravity. All wings are characterized by I*=0.1 and the flexibility ranges from Cy=0 (rigid wings) to Cy=15

Download Tam supplementary movie(Video)
Video 1.8 MB

Tam supplementary movie

Side to side movies of flexible fluttering wings falling under the influence of gravity. All wings are characterized by I*=0.1 and the flexibility ranges from Cy=0 (rigid wings) to Cy=15

Download Tam supplementary movie(Video)
Video 3.7 MB

Tam supplementary movie

Side to side movies of flexible fluttering wings falling under the influence of gravity. All wings are characterized by I*=0.1 and the flexibility ranges from Cy=22 to Cy=60

Download Tam supplementary movie(Video)
Video 1.5 MB

Tam supplementary movie

Side to side movies of flexible fluttering wings falling under the influence of gravity. All wings are characterized by I*=0.1 and the flexibility ranges from Cy=22 to Cy=60

Download Tam supplementary movie(Video)
Video 3.5 MB