Recirculation Zone Structure and Dynamics in Confined Bluff-Body Turbulent Premixed Flames

Large eddy simulations are employed to study the effects of operating conditions on recirculation zone structure and dynamics downstream of confined bluff-body turbulent premixed flames. The influence of two reactant temperatures, 310 K and 900 K, is characterized for the strength, size, and shape of the three-dimensional vortical structures of the recirculation zone downstream of an equilateral triangle. For both operating conditions, “corner vortex structures” appear as transversely-oriented vortices that situate downstream of the boundary layer separation location on the spanwise walls, in the recirculation zone. The recirculation zone length and strength, the corner vortex structure width, and the vorticity and circulation of these vortices all increase as reactant temperature increases from 310 K to 900 K. A theoretical description of flat plate laminar boundary layers predicts the boundary layer separation points on the spanwise walls within 20% of the simulations, indicating that boundary layer separation is likely due to the adverse pressure gradient within the recirculation zone. This suggests a mechanism for predicting the presence, size and strength of “corner vortex structures” in bluff-body stabilized flames.