Hybrid Manipulation of Streamwise Vorticity in a Turbulent Boundary Layer*

Manipulation of streamwise vorticity in a turbulent boundary layer is investigated experimentally at high subsonic speeds ($M$~=~0.5) along converging-diverging duct wall designed to provide an adverse pressure gradient that mimics the pressure gradient in a typical offset diffuser. Counter-rotating vortex pairs and single-sense vortices are formed and characterized using conventional passive sub-boundary layer micro-ramps and micro-vanes, respectively. Fluidic analogues of these passive devices are established by using surface-mounted synthetic jet actuators. Hybrid manipulation of streamwise vorticity within the boundary layer is demonstrated by simultaneous combination of passive and active actuation which enables robust, controllable ``fail-safe'' operation that requires no net mass injection.