Effect of Streamwise Vortices on Scramjets Porthole Injection Mixing

The use of Scramjets for space access could lead to important reductions in cost for satellite placement in Low Earth Orbit (LEO) and Sun-synchronous Orbit (SSO). The design of a fully operating Scramjet has proven extremely challenging, due to different issues. One of these is efficient fuel-air mixing, a prerequisite for efficient fuel combustion within the short air residence time during supersonic combustion. It has been suggested that streamwise vortices, either naturally generated by the Scramjet intake geometry, or artificially generated by vortex generators, could be used to enhance the mixing rate of fuel in air. This work presents a numerical study of the interaction between the fuel plume of a porthole injector and streamwise vortices, with focus on the effect on mixing. Flow conditions representative of a Mach 12 flight and equivalent ground-based Scramjet test conditions are investigated. The results show a significant enhancement in fuel penetration and mixing. This numerical investigation quantifies the increase in mixing efficiency that can be attained in a canonical geometry by tailoring the fuel jet location to exploit naturally occurring streamwise vortices. Three different vortex intensities, two different injector locations and two different injection to free stream momentum ratios are investigated. The relevant mechanisms driving the mixing enhancement and the best injector location are identified.