Proportional control of asymmetric forebody vortices

The ability of the unsteady bleed technique to control the asymmetry of the steady tip vortices separating from a forebody model is demonstrated. Mean velocity profiles measured behind the forebody model at alpha = 45 deg and Re = 6.3 x 10(3) clearly show the exponential spatial growth of the disturbance in the wake. This exponential growth is consistent with a spatial type of flow instability. The type of spatial instability governing the flow determines the behavior of the vortex system. The continuous variation of vortex position with control input found at alpha = 45 deg is consistent with a convective type of instability and allows proportional control of the forebody vortices with very low forcing amplitudes and input power levels. The forebody wake shows characteristics similar to a global type of instability for the bistable behavior found at alpha = 55 deg. For the global type of flow instability, the vortex system is locked into one of two stable configurations, and proportional control does not seem feasible under these conditions.