Large eddy simulation of impinging flames: Unsteady ignition and flame propagation

Abstract

The dynamic processes of ignition and turbulent flame development in a turbulent impinging flame are studied using large eddy simulation (LES). The Dynamic Thickened Flame (DTF) model is extended to incorporate realistic chemical mechanisms to simulate the partially premixed flames due to flame impingement on a solid wall. A new chemical mechanism with 22 species 66 steps is developed for propane. This LES formulation correctly reproduces the different ignition and turbulent flame dynamics under three different ignition conditions corresponding to experiments. Combustion modes formed by the impinging propane flame are investigated using the flame indicator and chemical explosive modes analysis, which reveals the existence of both turbulent premixed and diffusion flames. The extent and strength of premixed and diffusion flame modes, respectively, are strongly influenced by the ignition location relative to the wall. The corresponding thermal expansion leads to different flow and mixing processes, which in turn affects the subsequent flame development. The variation of the overall heat release with time is different for the three ignition locations, reflecting different contributions from the premixed and diffusion flames, respectively.