Leading edge vortex (LEV) formation, which is initiated by separation at the leading edge, depends on airfoil shape, Reynolds number, rate of translation/rotation, amplitude of motion and the pitch axis location. The Leading Edge Suction Parameter (LESP) derived from inviscid theory, serves to predict the onset LEV formation for any unsteady motion using a critical value that depends on the airfoil shape and Reynolds number of operation. In this paper, the critical LESP value is determined for different airfoils over a range of Reynolds numbers. The SD7003 airfoil was used as a baseline and modified airfoils were derived by altering the leading edge radius, keeping maximum thickness unchanged. Increasing the leading edge radius resulted in higher critical LESP values, demonstrating that separation is delayed for flow over a more rounded leading edge since it can support more suction. The effect of Reynolds number was more complicated, with the critical LESP decreasing from Re = 5,000 to Re = 100,000, and increasing after. Hence conditions which promote and suppress leading edge vortex formation were identified, and the critical LESP values were made available over a broad range of parameters, which can be used for low-order prediction and modeling of complicated, vortex-dominated flows.
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