LES of spray combustion in swirling flows

The ability to predict turbulence-chemistry interactions in realistic full-scale gas turbine combustors has not been feasible until now due to the lack of simulation models and computing power. Here, a massively parallel large-eddy simulation model for spray combustion has been developed and utilized to investigate the unsteady interactions between spray dispersion, vaporization, fuel-air mixing and heat release in a realistic combustor. The effects of swirl intensity and heat release are investigated. Results show that swirl drastically increases the droplet dispersion and that the central toroidal recirculation zone (which is a manifestation of the vortex breakdown process) occurs only under high-swirl conditions. Also, combustion and heat release tends to reduce the size of this recirculation zone, due to an increase in flow acceleration associated with heat release. It is also observed that in the presence of swirl, large-scale organized structures are subjected to complex stretch effects due to a combination of streamwise and azimuthal vortical motions. Increase in swirl accelerates the breakdown of these structures due to this stretch effect, leading to enhanced fuel-air mixing.