Flame Stabilization Modes in Lean Premixed Swirl Stabilized Combustion

Abstract

Flame holding and its propagation characteristics in a lean premixed swirl stabilized combustor is studied using large eddy simulations (LES) with a goal to understand the different stabilization modes seen in an experimental combustor, which combines swirl inflow with a central bluff body to create multiple stabilization locations. Experimentally observed transition from a flame stabilized along the inner shear layer to a flame that exists both in the inner and the outer shear layer are numerically simulated by just an increase in the equivalence ratio, as done in the experiment. Comparison with experimental data shows excellent agreement and confirms the ability of LES to capture these different flame stabilization processes without adhoc model adjustments. Despite the change in heat release, the large scale flow features such as the vortex bubble breakdown and recirculation behind the dump expansion remain similar for each case. This indicates that the flame in the outer shear layer does not affect the flow substantially. Simulation results are also used to understand the difference in the unsteady flame structure under these operating conditions.