Use of Supersonic Microjets for Active Separation Control in Diffusers

Abstract

Inlets to aircraft propulsion systems must supply flow to the compressor with minimal pressure loss, distortion or unsteadiness. Flow separation in inlets and ducts can reduce the overall system performance. The present paper describes an experimental investigation carried out to study the feasibility of using supersonic microjets to control boundary layer separation in an adverse pressure gradient. The geometry used for this study is a simple diverging “Stratford ramp” equipped with arrays of 400!m supersonic microjets. Measurements include detailed surface flow visualizations, surface pressure distributions, flow visualizations and velocity field measurements using Particle Image Velocimetry. The results clearly indicate that by activating these microjets, the separated flow was eliminated. This was achieved with minimal mass flux, lower than 1.5 % of the primary flow. The activation of microjets and the resulting elimination of separated flow led to a significant increase in the momentum of the flow near the surface. The increase in momentum was at least an order of magnitude higher than the momentum injected by the microjets. As such, supersonic microjets appear to be very effective actuators for separation control.