Introduction to Shock Wave-Boundary Layer Interaction and Unstart in Supersonic Inlets

Abstract

A supersonic aircraft is designed to exceed the speed of sound in its normal flight configurations. Supersonic aircrafts are affected by shock waves which are prime importance in air intakes whose purpose is to provide a stable, uniform, low-loss, subsonic flow to the engine face at all flight conditions. Oblique shock waves are an efficient form of compression; however, they interact with the boundary layer forming on the inlet walls. The shock-induced adverse pressure gradient can trigger large-scale separation, resulting in significant total pressure loss and flow distortion. Furthermore, the unsteady aspects of separated shock-wave/boundary-layer interactions (SWBLI) can cause large structural loads and may even lead to inlet unstart. During unstart, the original inlet shock system can eventually take the form of a detached bow shock that resides upstream of the inlet entrance. The unstart process can be severe with high transient pressure loads and it can lead to a loss of engine thrust. In order to eliminate or reduce the effects of these interactions their characteristics must be analyzed and active/passive control techniques must be employed.