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First published online March 14, 2005
Journal of Experimental Biology 208, 1079-1094 (2005)
Published by The Company of Biologists 2005
doi: 10.1242/jeb.01471
The aerodynamics of Manduca sexta: digital particle image velocimetry analysis of the leading-edge vortex
1 Department of Zoology, University of Oxford, South Parks Road, Oxford, OX1
3PS, UK
2 College of Aeronautics, Cranfield University, Cranfield, MK43 0AL,
UK
* Author for correspondence (e-mail: Richard.Bomphrey{at}zoology.oxford.ac.uk)
Accepted 21 December 2004
Here we present the first digital particle image velocimetry (DPIV) analysis of the flow field around the wings of an insect (the tobacco hawkmoth Manduca sexta, tethered to a 6-component force-moment balance in a wind tunnel). A leading-edge vortex (LEV) is present above the wings towards the end of the downstroke, as the net upward force peaks. Our DPIV analyses and smoke visualisations match the results of previous flow visualisation experiments at midwing, and we extend the experiments to provide the first analysis of the flow field above the thorax. Detailed DPIV measurements show that towards the end of the downstroke, the LEV structure is consistent with that recently reported in free-flying butterflies and dragonflies: the LEV is continuous across the thorax and runs along each wing to the wingtip, where it inflects to form the wingtip trailing vortices. The LEV core is 2-3 mm in diameter (approximately 10% of local wing chord) both at the midwing position and over the centreline at 1.2 m s-1 and at 3.5 m s-1 flight speeds. At 1.2 m s-1 the measured LEV circulation is 0.012±0.001 m2 s-1 (mean ± S.D.) at the centreline and 0.011±0.001 m2 s-1 halfway along the wing. At 3.5 m s-1 LEV circulation is 0.011±0.001 m2 s-1 at the centreline and 0.020±0.004 m2 s-1 at midwing. The DPIV measurements suggest that if there is any spanwise flow in the LEV towards the end of the downstroke its velocity is less than 1 m s-1. Estimates of force production show that the LEV contributes significantly to supporting body weight during bouts of flight at both speeds (more than 10% of body weight at 1.2 m s-1 and 35-65% of body weight at 3.5 m s-1).
Key words: flow visualisation, leading-edge vortex, Manduca sexta, hawkmoth, DPIV, particle image velocimetry, PIV, unsteady aerodynamics, flapping flight, micro air vehicle
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