Flow Dynamics Effected by Active Flow Control in an Offset Diffuser

Abstract

Total pressure distortions at the aerodynamic interface plane (AIP) of an aggressive double-offset diffuser that are induced by the formation of secondary vortices coupled with internal flow separation domains are mitigated by fluidic-based flow control. The presence of the secondary counter-rotating streamwise vortex pairs that form at each diffuser turn induces concentrations of total pressure deficit at the AIP by advecting low-momentum fluid from the wall region into the core flow. The effectiveness of fluidic actuation for suppression of the AIP distortions is demonstrated by implementing actuator arrays at the downstream diffuser turn that leads to over 60% reduction in the average circumferential distortion. Spectral and POD analyses of high-speed, time-resolved total pressure measurements at the AIP indicate that these counter-rotating vortex pairs are unstable exhibiting a frequency band centered about 1 kHz. The actuation alters the spectral content of the pressure fluctuations and leads to their broadband suppression that includes the unstable frequency band of the secondary vortices. The stabilization of the total pressure oscillations is reflected in suppression of not only time-averaged total pressure distortion, but it also reduces a spread of instantaneous distortion about its mean. Consequently, the peak instantaneous flow distortion is reduced by 25%.