Turbulent Combustion Modelling in Supersonic Flows for Applications to future RBCC vehicles

Mixing and combustion of supersonic reacting flows are currently under investigation for new generation RBCC vehicles. Because of the speed within the SCRJ combustor, the length required for fuel and air to mix and react is commonly thought to be a difficult compromise if friction drag is to be kept to a minimum. LES simulations can be an useful tool to better understand the physics of supersonic combustion. By simulating combustion and analyzing numerical results, it is possible to draw fundamental conclusions suggesting how to design a more efficient combustor. Thus the subgrid scale (SGS) model to be implemented as closure of the filtered Navier Stokes equations is critical in reproducing experimental results and giving credibility to numerical predictions. In the present paper, a new SGS model for supersonic reacting flows is being proposed. This model accounts for compressibility effects on mixing and combustion by introducing a complete equations for the subgrid kinetic energy transport. This equation accounts for the effect of heat release due to combustion, dilatation due to the compressibility of the fluid, and the pressure gradient that are responsible for the baroclinic term and then for streamwise vorticity and dissipation. The reaction rate accounts for the effect of the Mach number by means of the SGS Mach number squared. The effect of the small scales scalars fluctuations on turbulent mass diffusivity is included by modeling the local Schmidt number.