Fluidic Control of an Aggressive Offset Diffuser for a Supersonic Inlet

Losses and flow distortions in a supersonic-inlet aggressive offset diffuser (Mthroat < 0.64) that are induced by closed, separated flow domains on the diffuser’s concave surfaces and by pairs of dynamically coupled counter-rotating streamwise vortices are mitigated using fluidic actuation. While pressure recovery is primarily limited by the separation in each of the diffuser’s turns, the distortion is governed by counter-rotating streamwise vortices that advect low-momentum fluid from the wall region into the core flow. The present investigations have shown that the secondary vortices are engendered by concentrations of streamwise vorticity that form in the outboard segments of the separated flow domains. Therefore, fluidic control of the scale and topology of the trapped vorticity within the internally-separated flow can be leveraged to control the structure and strength of the ensuing secondary vortices and thereby significantly reduce flow distortion and losses. In the present investigations, fluidic control is effected by a spanwise array of oscillating jets that are placed just upstream of the separation domain. The actuation alters the spacing and diminishes the strength of the base flow streamwise vortices by forming and adjoining streamwise vorticity concentrations of opposite sense. The spanwise distribution of the actuator array can be optimized to reduce the average circumferential distortion by as much as 60% at actuation to diffuser mass flow rate ratio of 0.4%.