LARGE-EDDY SIMULATION OF A BLUFF-BODY FLAME AND THE FORCED IGNITION PROCESS

Bluff-body burners are widely used in combustion chambers of industrial equipment such as jet engines, gas-turbines and boilers. Safe operation and low pollutant emission in these equipment directly demands understanding and controlling of ignition process in bluff-body burners. In this paper, a large-eddy simulation based on steady flamelet/progress variable approach was applied in a turbulent non-premixed bluff-body flame and its ignition process. Simulating two cases including non-reacting bluff-body flow (NRBB) and Sydney methane/hydrogen flame (HM1E), we comprehensively compared statistical results with experimental measures and previous numerical investigation. Then, we presented an instantaneous ignition process and flame development in Sydney bluff-body burner. Finally, the ignition process was analysed and characterized in detail, and a four-step process of flame ignition was proposed:decaying of ignition source, ignition initiation, generating of ignition kernel, and ignition success, which was identified by variation of peak values of temperature, OH and CH₂O mass fraction. In addition, the ignition kernel stayed at the stern of the outer vortex in the recirculation zone of the cold flow of the bluff-body burner.