Subgrid mixing and molecular transport modeling in a reacting shear layer

Abstract

The importance of molecular transport in high-Reynolds number reacting flows is now well accepted because of incontrovertible experimental evidence. However, most mixing models neglect this small-scale process and, as a result, fail to predict the observed variation of the mean mixed composition and the Reynolds number, Schmidt number, and Damköhler number dependence observed in the experiments. A mixing model that explicitly accounts for the small-scale mixing, molecular transport, and chemical kinetics processes was developed earlier as a stand-alone method by Kerstein. Here, this linear eddy model (LEM) is implemented as a subgrid model within a configuration-independent simulation methodology based on large eddy simulation (LES) and used to study scalar mixing in a low-heat release mixing layer. The ability of the present method to capture correctly the small-scale mixing and molecular transport effects is demonstrated by carrying out both qualitative and quantitative comparisons with experimental data obtained in high-Reynolds number flows. The present method provides a unique modeling capability to handle the small-scale processes within the context of a general LES approach without any ad hoc closure of the scalar equations.