Modelling local extinction in Sydney swirling non-premixed flames with LES/CMC

The Large Eddy Simulation (LES) and three dimensional CMC (3D-CMC) model are applied to simulate the Sydney swirl-stabilized non-premixed methane flames with different levels of local extinction. The CMC model is implemented with a finite volume formulation, unstructured mesh and detailed chemistry. The statistics of velocity, mixture fraction, and major species mass fractions in both physical and mixture fraction space demonstrate very good agreement with the measured results. The level of local extinction with increased fuel bulk velocity velocities is reasonably captured. In addition, the location where flame extinction first occurs also agrees with the experimental observations. However, the statistics of the hydroxyl mass fraction, a very sensitive indicator of local extinction, have some differences from the experimental data. Budget analysis of individual terms in the CMC equation for the hydroxyl mass fraction shows that conditional convection in the CMC model has a significant role in inducing both local extinction and re-ignition events. The conditional dilatation flux contributes only when the local heat release rate is significant.