"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...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 [Reynolds numbers - mostly affected by insect's size]." (Birch et al. 2004:1063)
Force production and flow structure of the leading edge vortex on flapping wings at high and low Reynolds numbers
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