Investigation of Trapped Vorticity Concentrations Effected by Hybrid Actuation in an Offset Diffuser

Trapped vorticity concentration engendered by deliberate modification of the internal surface of an offset diffuser is coupled with a spanwise array of surface-integrated fluidic-oscillating jets for hybrid flow control of the secondary flow that gives rise to flow distortions. The trapped vorticity mimics the effects of local separation within aggressive diffusers and is used as a testbed for investigations of the effectiveness of such hybrid flow control for alleviation the flow distortions at the engine inlet (AIP). The local and global characteristics of the diffuser flow in the absence and presence of the actuation are investigated at Mach numbers up to M = 0.7, using a forty-probe AIP total pressure rake, surface oil-flow visualization, hot-wire anemometry, and particle image velocimetry. The present investigations demonstrate that the actuation affects the strength and scale of the trapped vorticity and its interaction with the cross flow, and consequently alters the flow evolution within the diffuser and leads to significant suppression of pressure distortion at the AIP (by about 80%). These findings indicate that hybrid actuation based on trapped vorticity concentrations can be utilized for mitigation of flow distortion in diffuser flows by strong coupling to the natural formation of vorticity concentrations due to the local flow separation.