Control of Aerodynamics Instabilities of a Slender Axisymmetric Body at High Incidence*

The aerodynamic loading and stability of a wire-mounted slender cylinder (L/D = 9) with an ogive forebody are investigated in wind tunnel experiments at high angles of incidence (45° < α < 60°).  Within this incidence range, the counter rotating vortex pair that normally forms over the forebody evolves asymmetrically in a manner that depends on its azimuthal orientation such that the interaction between the vortex pair and the cylinder's near wake vortices induces a nominally stable side force whose sense depends on the forebody's orientation.  However, within a critical range of incidence angles and forebody orientations the interaction between the forebody and wake vortices undergoes unstable mode switching that is accompanied by time-periodic side forces which couple to strong unstable, predominantly lateral oscillations of the cylinder within its body-yaw plane.  The present investigations have demonstrated the effectiveness of fluidic actuation using a synthetic jet placed at the juncture of the forebody and the cylinder for decoupling between the interactions of the forebody unstable vortex pair and the wake and thereby suppressing the side force oscillations and the lateral yaw instability.  It is shown that the actuation is effective both at fixed incidence and during pitch up/down maneuvers of the cylinder.