Numerical solution of non-premixed reactive flows in a swirl combustor model

A mathematical model has been developed to study turbulent, confined, swirling flows under reacting nonpremixed conditions. The model solves the conservation equations of mass, momentum, energy, species, and two additional equations for the turbulent kinetic energy and the turbulent length scale. Combustion has been modelled by means of a one-step overall chemical reaction. The numerical predictions based on the eddy-break-up model of turbulent combustion show a recirculation zone in the form of a one-celled toroidal vortex at the combustor centerline. High levels of turbulence characterize the recirculation zone, whose diameter and velocity first decrease and then increase as the magnitude of the outer swirl number is first decreased from counter-swirl to zero and then increased to co-swirl flow conditions. Counter-swirl produces steeper velocity gradients at the inter-jet shear layer, promotes faster mixing and yields better combustion efficiency than co-swirl. The numerical results are compared with those obtained under non-reacting conditions in order to assess the influence of the heat release on the size of the recirculation zone.