Applications of shock-induced mixing to supersonic combustion

Abstract

Families of two-dimensional, unsteady shock-induced vortical flows are simulated numerically. The flows consist of one or more regions of light gas, surrounded by heavy gas, being overtaken by a normal shock wave. The interaction of the density gradient at each light/heavy interface with the pressure gradient from the shock wave generates vorticity. This causes the light gas regions to roll up into one or more counter-rotating vortex pairs, which stir and mix the light and heavy gases. The mixing is characterized by an asymptotic stretching rate. The effects of shock strength, light/heavy gas density ratio, and geometry on the mixing are investigated. These two-dimensional, unsteady flows are analogous to three-dimensional, steady flows that may be used in SCRAMJET combustors demanding rapid and efficient mixing of fuel and oxidizer. For such applications, 1) the fuel injectors should be elongated in the direction of the shock; 2) multiple smaller injectors are preferable to a single larger injector; 3) injectors should be arranged in groups of closely spaced pairs, rather than uniformly; and 4) multiple shock waves should be utilized, if possible.