Application of unstrained flamelet SGS closure for multi-regime premixed combustion

Large eddy simulation of turbulent premixed combustion behind a bluff-body is performed using unstrained flamelet model with a presumed probability density function to calculate filtered reaction rate. The subgrid variance of the progress variable required in this approach is calculated using its transport equation to include contributions from reaction, turbulence and molecular diffusive and dissipative processes at sub-grid scales. The dissipation rate of the variance is obtained using an algebraic closure, which maintains physical consistency among turbulence, reaction and molecular diffusion. Various quantities such as mean velocity, temperature and species mass fractions computed for two bluff-body flames experiencing 2% and 24% turbulence intensities are compared to their respective measurements. These comparisons are very good suggesting that the unstrained flamelet SGS closure works well for multi-regime combustion. The demonstrated success of this modelling framework is explained on a physical basis.