Experimental and Numerical Investigation of Controlled Flow Distortion in a Subsonic Offset Diffuser by Trapped Vorticity

Controlled concentrations of trapped vorticity within a recess in the moldline of an offset subsonic (M < 0.7) diffuser are explored for active suppression of flow distortions in joint experimental/numerical inveatigations. The coupling between the trapped vorticity that models inherent flow separation and the global secondary counter-rotating streamwise vortices that give rise to flow distrotions is manipulated using a spanwise array of fluidic oscillating jets that are distributed across the diffuser span just upstream of the trapped vortex. The actuation modifies the topology of critical (saddle and node) points of the trapped vortex and thereby has a profound effect on the structure of the secondary flow. It is shown that optimal interactions of the actuation with the trapped vortex can lead to full suppression of the central vortex pair and redistribute the residual vorticity along the diffuser’s corners. These structural changes result in significant reduction of flow distortion by about 68% (measured by the average circumferential distortion parameter) at actuation mass flow rate that is only 0.25% of the diffuser mass flow rate.