Self-excited flag vibrations produce post-stall flow control

Abstract

A small flag attached to the surface of an airfoil near the leading-edge exhibits self-excited oscillations when the airfoil is set at a post-stall angle of attack. The limit cycle oscillations of the flag between the airfoil surface and the freestream produce leading-edge vortices periodically, resulting in a remarkable increase in the maximum lift coefficient and stall angle. There are strong similarities between this passive flow control method, which relies on the fluid-structure interactions, and the active flow control methods in producing post-stall lift enhancement.