Modeling chemical flame structure and combustion dynamics in LES

Abstract

In turbulent premixed combustion, the instantaneous flame thickness is typically thinner that the grid size usually retained in Large Eddy Simulations (LES), requiring adapted models. Two alternatives to couple chemical databases with LES balance equations, the Thickened Flame (TFLES) and the Filtered Tabulated Chemistry (F-TACLES) models, are investigated here and compared in terms of chemical flame structure and dynamics. To avoid the uncertainties related to the modeling of sub-grid scale turbulence/flame interactions, this comparison is conducted in situations where the flame front is not wrinkled at sub-grid-scale levels. The thinner quantity requiring an accurate discretization on the numerical grid mesh is the reaction rate of the thickened or filtered progress variable. The thermal flame structure is found to be considerably thicker in TFLES than when using F-TACLES. The simulation of a 2D unsteady Bunsen burner flame shows that the thermal thickness spreading strongly affects the flame dynamics giving a decisive advantage to F-TACLES compared to TFLES.