LES of Supersonic Combustion with a variable Schmidt number

LES simulations of supersonic reacting flows could be a valid help in designing combustors for hypersonic airbreathing vehicles if a subgrid scale model suitable to supersonic flows is implemented. In particular, the effect of compressibility on mixing and on combustion must be taken into account when modelling the effect on large scales of fluctuations of the fluid dynamics variables due to fine turbulent structures. In fact, in LES, all scales above the filter dimension are calculated by means of the Navier Stokes equations, the smaller ones are modelled. In the present work, the novel ISCM model has been implemented. This model accounts for compressibility effects on mixing and on combustion by introducing a complete equations for the subgrid kinetic energy transport. In particular, micro-scales physics in this subgrid kinetic energy equation is algebraically modelled to provide the velocity fluctuations needed by an "eddy viscosity" SGS closure. The effect of the small scales scalars fluctuations on turbulent diffusivity is also accounted for in this SGS model. In fact, it is shown that in supersonic regime, where combustion is very fast, these fluctuations become more and more important and their contribute must be taken into account to better predict supersonic mixing. LES performed with this new model predict a newly defined turbulent Schmidt number ranging from 0.1 to 0.4. Copyright © 2008 by the American Institute of Aeronautics and Astronautics, Inc. All rightsreserved.