Numerical investigation of mixing and combustion enhancement in supersonic combustors by strut induced streamwise vorticity

A numerical study of mixing and combustion enhancement has been performed for a Mach 2 model scramjet (supersonic combustion ramjet) combustor. Fuel (hydrogen) is injected at supersonic speed through the rear of a lobed strut located at the channel symmetry axis. The shape of the strut is chosen in a way to produce strong streamwise vorticity and thus to enhance the hydrogen/air mixing. Strength and size of the vortices are defined by the strut geometry and may be modified. It will be shown that in comparison to planar struts the mixing efficiency is strongly improved. On the other hand, the induced vortices cause an increase in entropy and larger losses in total pressure. Different planar and lobed strut injectors are investigated numerically and a comparison with experimental data is given for cold supersonic mixing. Based on this study a numerical investigation of flame stabilization and fuel burnout is performed where two stable modes of combustion are identified. They are associated with attached or detached flames depending on the chosen inflow conditions. In both cases subsonic regions at the channel symmetry axis are responsible for flame holding. If the combustor geometry is chosen in a favorable way these subsonic zones may be kept small. Moreover, the flames are away from solid walls thus minimizing the wall heat load.