Control of Scramjet Inlet Recirculations Using Fuel Injection

Abstract

A novel approach using ramp fuel injectors is here proposed to reduce or eliminate shock-induced recirculation regions in scramjet inlets. The study is performed using UArizona’s CFDWARP code solving the Favre-averaged Navier–Stokes equations closed by the revised Wilcox [Formula: see text] model with dilatational dissipation and rapid compression corrections. The results obtained are representative of hydrogen fuel injected after the second shock of a three-shock scramjet inlet at a flight Mach number of 7.5 and an altitude of 34 km. Injecting fuel in the inlet leads to particularly high values of the cross-stream velocities that reduce the size of the recirculation bubbles. This is attributed to be due to i) large cross-stream shearing created by the bow shock above the ramp injectors, to ii) the large density difference between the fuel and the air leading to baroclinicity, and to iii) the greater acceleration of the light fuel by the pressure gradients. As opposed to previous methods that achieved partial reduction of the separation region, fuel injection can lead to a complete elimination of the recirculation bubbles in scramjet inlets. To eliminate recirculations, only half of the fuel needs to be injected in the inlet with the rest injected in the combustor as usual.