Flame Annihilation Displacement Speed and Stretch Rate in Turbulent Premixed Flames

摘要

This paper examines the dynamics of flame annihilation in turbulent premixed flames using a DNS dataset of Haghiri et al. (J. Fluid Mech. 843, 29 2018). Two theoretical frameworks are considered. The relative contributions of the reaction rate, normal diffusion and flame curvature to the flame displacement speed are first considered. A revised form of Markstein's theory describing the displacement speed as a function of the local Karlovitz number is then used, including consideration of the relative importance of strain rate and curvature. Comparison of the statistics of flame annihilation to those of the entire flame surface suggests that this modified Markstein number might be sufficient to estimate the displacement speed for most annihilation events. This has important implications for level-set type combustion modelling where correct prediction of the displacement speed is a key part of describing the evolution of the flame surface. Given the significance of flame annihilation in sound generation by turbulent premixed flames (Haghiri et al. J. Fluid Mech. 843, 29 2018; Brouzet et al. Combust. Flame 204, 268 2019), these findings also have implications for the modelling of premixed combustion noise.