Large-eddy simulation of a reacting scalar mixing layer with arrhenius chemistry

A method for predicting filtered chemical species concentrations and filtered reaction rates in large-eddy simulations of nonpremixed, nonisothermal, turbulent reacting flows has been previously demonstrated to be,quite accurate for higher Damköhler numbers and simple chemistry. The method extends quasi-steady flamelet concepts to model reactions that occur at lengths smaller than those resolved on the numerical grid. In this paper, the method is more fully tested using predictions of filtered mass fractions, temperatures, and reaction rates in an incompressible scalar mixing layer. One- and two-step reactions are considered, with activation temperatures and stoichiometric mixture fractions typical of reactions that occur in natural and engineering processes. The predictions for the mass fractions and temperatures are excellent in all cases considered for which quasi-steady flamelet modelling is appropriate. The predictions of the filtered reaction rates are also very good, even for cases where the reaction zones are very thin. Also demonstrated is a one-parameter model for the probability density of the subgrid-scale dissipation rate that significantly improves the predictions of the filtered reaction rates.