Numerical Investigation of the Effect of Inflow Mach Number on Fuel Mixing in a Supersonic Cavity Combustor

The flow-field and fuel-air mixing dynamics are examined under varying inflow Mach number conditions in an ethylene-fueled supersonic cavity combustor. Three-dimensional Reynolds Averaged Navier-Stokes (RANS) simulations were performed to analyze the flow-field characteristics under flight Mach numbers of 5 and 10. Gaseous ethylene is injected upstream of the cavity at the sonic condition at constant momentum flux perpendicular to the flow in the channel to examine the impact inflow Mach number has on fuel-air mixing efficiency. Adaptive mesh refinement (AMR) is implemented based on the static pressure gradient and fuel mass fraction to capture the shock structure formed by the fuel injection fuel mixing. The results indicate strong vorticity generated at the interface of between the free stream air and fuel jet for both conditions. The primary difference between the conditions is the weaker recirculation region generated within the cavity, which does not interact as significantly with the fuel jet for the Mach 10 condition. As a result, a higher mass fraction of fuel is able to enter the cavity resulting in less complete mixing across the length of the combustor. The mixing efficiency is quantified for both conditions and reveal an approximately 16\% decrease across the entire combustor under the higher Mach number condition.