Scalar fluctuation modeling for high-speed aeropropulsive flows

A Reynolds-averaged Navier-Stokes-based scalar-variance model is described that extends a previous low-speed nonreacting jet model to more generalized high-speed compressible reacting flows. The model is cast in a k-epsilon turbulence model framework. Transport equations for energy variance and its dissipation rate are solved to predict temperature fluctuations and provide a thermal time scale for use in calculating a variable turbulent Prandtl number. For multispecies; problems, mixture-fraction variance and dissipation rate equations are solved that predict species concentration fluctuations and provide a species mixing time scale for use in calculating a variable turbulent Schmidt number. The formulation accounts for compressibility and near-wall damping effects. A series of high-speed flow simulations are presented for both nonreacting and reacting configurations and the predictions are compared to available measured data and companion LES calculations. Results demonstrate the models' capabilities over a range of conditions and suggest that the proposed formulation will provide improved predictions in practical high-speed aeropropulsive configurations of interest, such as scramjet combustors, where turbulent Prandtl and Schmidt numbers vary substantially.