Investigation of Modeling for Non-Premixed Turbulent Combustion

A method for predicting filtered chemical species concentrations and filtered reaction rates in Large-Eddy Simulations of non-premixed, non-isothermal, turbulent reacting flows has been demonstrated to be quite accurate for higher Damköhler numbers. This subgrid-scale model is based on flamelet theory and uses presumed forms for both the dissipation rate and subgrid-scale probability density function of a conserved scalar. Inputs to the model are the chemistry rates, the Favre-filtered scalar, and its subgrid-scale variance and filtered dissipation rate. In this paper, models for the filtered dissipation rate and subgrid-scale variance are evaluated by filtering data from 5123-point Direct Numerical Simulations of a single-step, isothermal reaction developing in the isotropic, incompressible, decaying turbulence field of Comte-Bellot and Corrsin. Both the subgrid-scale variance and the filtered dissipation rate models (the ”sub-models”) are found to be reasonably accurate. The effect of the errors introduced by the sub-models on the overall model is found to be small, and the overall model is shown to accurately predict the spatial average of the filtered species concentrations over a wide range of times.