Aerodynamic Control of Forebody Flow Asymmetries on a Slender Cylinder at High Incidence using Azimuthal Bleed

Inherent instability of the forebody vortices that form on a cylinder at high incidence in a uniform cross flow and their interactions with the cylinder's near wake leads to unpredictable asymmetric aerodynamic loads especially in yaw. This instability is controlled by using bleed of the surface flow over the forebody through segmented azimuthal surface porosity that leads to prescribed formation of the forebody vortices and thereby induced side forces of prescribed magnitude and direction. Small-scale features of the interaction of the autonomous bleed with cross flow over the forebody and the evolution of the forebody vortices are captured using the high-resolution PIV measurements in multiple planes normal to the cylinder's axis. It is shown that bleed flow driven merely by pressure differences along the forebody surface and regulated by an internal louver shell can prescribe stable asymmetries of the forebody vortices and thereby impose side force and yaw moment of desired magnitude and sense. Moreover, the time-dependent actuation of the bleed louver enables the temporal variations of the induced aerodynamic loads on 2-3 convective time scales of the model.