Flame Stabilization Mechanisms in Lifted Flames
Flame stabilization and the mechanisms that govern the dynamics at the flame base of lifted flames have been subject to numerous studies in recent years. A combined Large Eddy Simulation-Conditional Moment Closure (LES-CMC) approach has been successful in predicting flame ignition and stabilization by auto-ignition, but accurate modelling of the competition between turbulent quenching and laminar and turbulent flame propagation at the anchor point had not been demonstrated. This paper will consolidate LES-CMC results by analysing a wide range of lifted flame geometries with different prevailing stabilization mechanisms. The simulations allow a clear distinction of these mechanisms. It is corroborated that LES-CMC accurately predicts the competition between turbulence and chemistry during the auto-ignition process, the dynamics of turbulent flame propagation can be captured, however, the dynamics of the extinction process are not approximated well under certain conditions. The averaging process inherent in the CMC methods does not allow for an instant response of the transported conditionally averaged reactive species to the changes in the flow conditions and any response of the scalars will therefore be delayed. The dimensionality of the CMC implementation affects the solution and higher dimensionality does no necessarily improve results. Stationary or quasi-stationary conditions, however, can be well predicted for all flame configurations.
KeywordsTurbulent reacting flows Partial premixing Lifted flames LES
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