Controlled Flow in a Serpentine Diffuser with a Cowl Inlet

Abstract

Total-pressure losses and distortion in a serpentine diffuser with a cowl inlet are investigated experimentally and computationally over a range of flow rates (Mach numbers at aerodynamic interface plane MAIP of up to 0.6). The present investigations show that, in the presence of the cowl, the diffuser flow is dominated by two pairs of counter-rotating streamwise vortices that are shed from the swept edges of the cowl lip. The subsequent evolution and unsteady interactions of these vortices result in significant total-pressure losses that are coupled with high dynamic distortion at the aerodynamic interface plane. These losses and distortions are strongly mitigated by deliberately drawing ambient air across the cowl surface to form jets that interact with the cowl flow along its inner surface. The jets are formed through spanwise slots across the surface of the cowl by exploiting the pressure difference effected by the cowl flow. The interaction of these jets with the cowl flow alters the formation and evolution of the streamwise vortices, suppressing their interactions and thereby significantly diminishing the losses and distortion across the full operating range of the diffuser. For example, at MAIP=0.5, the total-pressure recovery increases by 8% while the peak circumferential distortion decreases by 35%.