Unstructured LES-CMC modelling of turbulent premixed bluff body flames close to blow-off

A finite volume Large Eddy Simulation-Conditional Moment Closure formulation (CMC) was employed to turbulent premixed bluff body CH 4 -air flames at conditions far from (A1) and close to (A4) blow-off. The unstructured topology of the CMC grid allowed refinement in regions where turbulence inhomogeneity is expected providing an improved description of the turbulence-chemistry interaction phenomenon non-negligible at conditions investigated in this study. The simulations effectively reproduced the general trends especially considering the challenging conditions at very lean mixtures where the characteristic 'M'-shaped morphology of flame A4 and the significant increase in flame brush thickness compared to flame A1 was accurately replicated although overall flame heights were under-predicted. For flame A4 close to blow-off the calculation generally presented appreciable quantities of CH 2 O throughout the recirculation zone with isolated pockets of OH surrounded by high heat release in agreement with experimental findings. The simulation confirmed that in regions experimentally void of both CH 2 O and OH large quantities of partially reacted fluid were observed which entered the recirculation zone from the top