Active Flow Control of a Boundary Layer-Ingesting Serpentine Inlet Diffuser

Abstract

The effectiveness of active flow control for the reduction of flow distortion in boundary layer-ingesting serpentine inlets was examined. The intended purpose of the flow control was to redistribute the ingested low-momentum boundary-layer fluid around the periphery of the diffuser to reduce the flow distortion at the engine face. A variety of different blowing jet and suction hole configurations were analyzed using computational fluid dynamics, and a subset of these configurations was experimentally validated. Boundary-layer suction alone proved to be ineffective in reducing flow distortion, but suction did enhance the distortion reduction capability of blowing flow control when blowing mass flow rates were greater than 1% of the total inlet mass flow rate. To reduce the demand for bleed air from the engine compressor, it is suggested to augment blowing flow with the flow entrained from the suction holes using an ejector-pump concept. Application of the notional ejector-pump model resulted in a maximum decrease in engine-face distortion of 75% as measured by the parameter, as compared with a 28% reduction with blowing alone. Investigations also showed that the most practically effective flow control configurations maintained jet individuality to directly counter duct secondary flows while not combining to form large-scale vortices.