Meeting Abstract

100.8  Sunday, Jan. 6  The effect of aspect ratio on the stability of leading-edge vortices over insect-like wings PHILLIPS, N.*; KNOWLES, K.; BOMPHREY, R. J.; University of Oxford; Cranfield University; University of Oxford nathan.phillips@zoo.ox.ac.uk

Flying insects exhibit a vast range of wing planform shapes which vary widely in aspect ratio. In past CFD studies, it has been shown that the aspect ratio of an insect wing is a potentially important parameter in determining the stability of the leading-edge vortex (LEV), a lift-augmenting flow structure exploited by many insects, bats, and birds. Here, a stable LEV implies that it remains present on the upper surface of the wing throughout the wing stroke and does not detach and shed into the wake. An experimental investigation was conducted to investigate the potential effect of wing aspect ratio on the stability of the LEV. Experiments were accomplished with a custom-designed, mechanical flapping-wing apparatus (the ‘Flapperatus’) that mimics insect-like flapping-wing motion, with adjustable kinematics up to a 20 Hz flapping frequency in air. This approach enables highly repeatable wing kinematics to be achieved between test cases, thereby allowing the effects on flow structures caused by changes in wing aspect ratio to be observed in detail. Stereoscopic Particle Image Velocimetry (stereo-PIV) measurements of the flow field generated by wing planform shapes varying in aspect ratio were performed to characterize the formation, growth and stability of the LEV.