Investigation of modeling for non-premixed turbulent combustion

A method for predicting filtered chemical species concentrations and filter ed reaction rates in Large-Eddy Simulations of non-premixed, non-isothermal , turbulent reacting flows has been demonstrated to be quite accurate for h igher Damkohler numbers. This subgrid-scale model is based on flamelet theo ry 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 vari ance and filtered dissipation rate. In this paper, models for the filtered dissipation rate and subgrid-scale variance are evaluated by filtering data from 512(3)-point Direct Numerical Simulations of a single-step, isotherma l 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 reason ably 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 accu rately predict the spatial average of the filtered species concentrations o ver a wide range of times.