Passive control of self-induced roll oscillations using bleed

A passive flow control method, which uses bleed from a slot near the wing tip, has been shown to attenuate self-excited roll oscillations of a low aspect ratio (AR = 2) rectangular flat-plate wing. The effectiveness of the slot strongly depends on its location and width. For effective slot geometries, the tip vortex becomes more diffused, resulting in the elimination of the roll oscillations. Nonlinear interactions between the shear layers shed from the tip and the slot, as well as between the shear layer and the counter-rotating vortex may act as excitation, which can modify the response of the self-sustained oscillator. When the slot is located too close to the tip, there is rapid merging of the shear layers and less interactions, and the slot loses its effectiveness. Also, when the slot is narrow, there is insufficient bleed, resulting in less effective attenuation. Force measurements revealed that, this technique can be used as an effective method to suppress the roll oscillations without sacrificing the aerodynamic performance of the wing.