Two-dimensional direct numerical simulations were conducted to investigate the dynamics of lean premixed flames stabilized on a meso-scale bluff-body in hydrogen-air and syngas-air mixtures. To eliminate the flow confinement effect due to the narrow channel, a larger domain size at twenty times the bluff-body dimension was used in the new simulations. Flame/flow dynamics were examined as the mean inflow velocity is incrementally raised until blow-off occurs. As the mean inflow velocity is increased, several distinct modes in the flame shape and fluctuation patterns were observed. In contrast to our previous study with a narrow channel, the onset of local extinction was observed during the asymmetric vortex shedding mode. Consequently, the flame stabilization and blow-off behavior was found to be dictated by the combined effects of the hot product gas pocket entrained into the extinction zone and the ability to auto-ignite the mixture within the given residence time corresponding to the lateral flame fluctuations. A proper time scale analysis is attempted to characterize the flame blow-off mechanism, which turns out to be consistent with the classic theory of Zukoski and Marble.
Bibliographical noteKAUST Repository Item: Exported on 2020-10-01
Acknowledgements: The research reported in this publication was supported by funding from King Abdullah University of Science and Technology (KAUST) and computing cluster provided by KAUST Supercomputing Laboratory (KSL). The second author was partly supported by Advanced Research Center Program (2013R1A5A1073861) and Basic Science Research Program (2017R1A2B4003327) through the National Research Foundation of Korea.