Fluid dynamics modeling of a stratified disk burner in swirl co-flow

The work describes Large Eddy Simulations of an unconfined partially premixed propane-air burner with swirl. A premixing section consisting of two axisymmetric cavities, formed along three concentric disks, supplies the afterbody disk recirculation with a radial equivalence ratio gradient. Flame stabilization is established there supported by a swirling co-flow of air. Lean and ultra-lean conditions are examined by regulating the fuel-air stratification and the swirl. An implicit finite-volume LES method is applied, employing the dynamic Smagorinsky model and the Eddy Dissipation Concept. Propane combustion and NOx production are modelled with an eleven-step scheme. The LES reveals intrinsic features of the flame front anchoring close to the burner rim under the influence of inlet mixture stratification and reproduces large and small scale features of the primary vortex flame stabilization and its interaction with the downstream vortex breakdown zone. Comparisons with measurements indicate a satisfactory agreement in the mean and turbulent velocity fields, while the impact of combustion and heat release on the wake development is reproduced well by the model. Deviations in the mean and fluctuating fields increase in the vicinity of the interaction of the twin vortex system. Preliminary comparisons between simulations and global species measurements suggest that the turbulence-chemistry model represents satisfactorily the experimental trends.