Large eddy simulation of turbulent partially premixed flames with inhomogeneous inlets using the dynamic second-order moment closure model

Abstract

The Sydney piloted partially premixed flames with both homogeneous and inhomogeneous fuel/air inlets are studied using a dynamic second-order moment closure model in the framework of large eddy simulation with a four-step global reaction mechanism. The filtered reaction rates are directly closed using the second-order correlation moments of reactive scalars. Good agreements between LES and experimental data are obtained for time-averaged radial profiles, scatter plots and conditional profiles for mixture fraction, temperature and major species, demonstrating the capability of the model to reproduce the partially premixed flames. Further studies of the combustion characteristics of the two flames suggest that the coincident occurrence of high dissipation and reaction can weaken the flame stability for the homogeneous case, while the separation in the inhomogeneous case can help to enhance the stability. In the inhomogeneous case, the premixed flame is dominant upstream with a proportion of 70% to heat release and then decreases to about 40% downstream. The inhomogeneous conditions can establish a near-stoichiometric reactant belt with lower dissipation near the nozzle exit, which connects the hot pilot and central cold fuel/air mixture. Through this belt, the hot pilot gas can ignite the near-stoichiometric reactant in premixed mode by releasing significant heat and the flame can propagate upstream to form a stable flame.