NUMERICAL SIMULATION OF TURBULENT PREMIXED FLAMES USING THICKENED FLAME MODEL

This work numerically investigates the application of a Thickened Flame Model (TFM) for a premixed methane/air Bunsen flame (Chen F3 flame), using Large Eddy Simulation (LES) for turbulence and Finite-Rate Chemistry (FRC) for combustion. Due to a premixed flame front usually being very thin, a very fine mesh is required to resolve the flame structure if using LES/FRC. The TFM model has therefore been utilized to artificially increase the flame thickness without changing the flame speed, allowing the flame simulation on much coarser meshes. However, the thickening of a flame also reduces the capability of turbulent eddies to wrinkle the flame surface, leading to an underpredicted heat release rate. Efficiency functions have therefore been proposed for TFM to compensate for the reduced flame surface area and the lowered heat release rate. The state-of-the-art efficiency functions require an accurate estimation of the velocity fluctuations at the test filter scale that corresponds to the thickened flame thickness. This work compares different TFM efficiency functions and velocity fluctuation models for the Chen F3 flame, and validates the predicted flow variables against experimental data. The mesh resolution and numerical schemes have been carefully selected, offering a workflow for TFM simulations. The impacts of reaction mechanisms and chemistry acceleration tools, e.g., Dynamic Mechanism Reduction (DMR), on the solution accuracy and computational costs of the present LES/FRC simulations have also been evaluated.