An Investigation of Scalar Mixing Timescale Modelling in LES/FDF Simulations of Turbulent Premixed Flames

Predictive simulations of highly turbulent premixed flames are crucial though challenging for practical applications. In this study, a new closure of the scalar mixing timescale is formulated to enhance the predictability of large eddy simulation (LES)/filtered density function (FDF) simulations for turbulent premixed flames. Specifically, the new model integrates a dynamic subgrid closure for turbulence-induced micro-mixing with a hybrid mixing timescale model. It requires no tuning for the mixing model parameter CM and can dynamically consider contributions to subgrid mixing from turbulence and reaction respectively. Model evaluation is performed in LES/FDF simulations of the highly turbulent Sydney piloted premixed jet burner (PPJB) PM1-150 flame. It shows that the new model notably improves the predictions for the overall combustion progress and correctly predict the local extinction/re-ignition trend. Results further show that the mixing model parameter is significantly larger than the typical value (order of unity) used in Reynolds-averaged framework, highlighting the difference of the physical interpolation for this parameter. © 2021, Science Press. All right reserved.