Birch, James M. and Dickson, William B. and Dickinson, Michael H. (2004) Force production and flow structure of the leading edge vortex on flapping wings at high and low Reynolds numbers. Journal of Experimental Biology, 207 (7). pp. 1063-1072. ISSN 0022-0949 http://resolver.caltech.edu/CaltechAUTHORS:BIRjeb04
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The elevated aerodynamic performance of insects has been attributed in part to the generation and maintenance of a stable region of vorticity known as the leading edge vortex (LEV). One explanation for the stability of the LEV is that spiraling axial flow within the vortex core drains energy into the tip vortex, forming a leading-edge spiral vortex analogous to the flow structure generated by delta wing aircraft. However, whereas spiral flow is a conspicuous feature of flapping wings at Reynolds numbers (Re) of 5000, similar experiments at Re=100 failed to identify a comparable structure. We used a dynamically scaled robot to investigate both the forces and the flows created by a wing undergoing identical motion at Re of ~120 and ~1400. In both cases, motion at constant angular velocity and fixed angle of attack generated a stable LEV with no evidence of shedding. At Re=1400, flow visualization indicated an intense narrow region of spanwise flow within the core of the LEV, a feature conspicuously absent at Re=120. The results suggest that the transport of vorticity from the leading edge to the wake that permits prolonged vortex attachment takes different forms at different Re.
|Additional Information:||© The Company of Biologists Ltd 2004. Accepted 22 December 2003. First published online February 20, 2004. This work was supported by the Packard Foundation, the National Science Foundation (IBN-0217229) and DARPA (N00014-98-1-0855).|
|Subject Keywords:||insect flight, Reynolds number, aerodynamics, flow visualization|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Archive Administrator|
|Deposited On:||09 Jan 2009 07:28|
|Last Modified:||26 Dec 2012 10:41|
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