Large eddy simulation of turbulent stratified combustion using dynamic thickened flame coupled with tabulated detailed chemistry

A sub-grid scale (SGS) combustion model of the dynamic thickened flame (DTF) coupled with flamelet generated manifolds (FGM) approach (i.e. DTF-FGM) is developed to investigate Cambridge stratified flames. Two issues in developing the DTF-FGM model are addressed. Firstly, the copula method is extended to construct a multivariate joint probability density function (PDF) of the tabulated scalars. A modified laminar flamelet PDF is incorporated to describe the probable asymmetric multimodal distribution for the reaction progress variable. Secondly, large eddy simulation (LES) transport equations for the tabulated scalars, relevant sub-grid variances and covariance in the DTF-FGM model are deduced. LES of Cambridge stratified flames is performed with the DTF-FGM model and the widely used SGS combustion model which combines a presumed PDF with FGM (i.e. PPDF-FGM). Detailed comparisons between simulations and experiments are carried out to evaluate the SGS combustion models and mesh resolution effects. Meanwhile, an in-depth analysis for the flame structures of Cambridge stratified flames is also achieved. The results indicate that the developed SGS combustion model considering the effect of correlations between the mixture fraction and reaction progress variable has the ability to solve the stratified flame structures under LES mesh resolution exactly at a reasonable computational cost.