Effect of Flapping Frequency and Leading Edge Profile on Airfoil Leading Edge Vortical Structures

Hill Aerospace Museum, Conference Room

By varying leading edge geometry to wing profiles during flapping flight, Ozen and Rockwell observed a pattern of alternating spanwise vortices which minimized spanwise flow. As a follow up study to [1], this investigation explored the effect of flapping frequency on these previously observed streamwise vortical structures. By increasing the flapping frequency, the alternating streamwise vortices resulting from a sinusoidal leading edge became stretched in the path of the wing due to an increase of wing cross-radial velocity. The streamwise vortices are shown to minimize spanwise flow even after being stretched. Instabilities were formed at higher flapping frequencies (f = 0.2 Hz) due to velocity shear generated by the large cross-radial velocity. These instabilities began to break down the alternating streamwise vortices resulting in the development of a different flow structure including an increase of spanwise flow.