Large-eddy simulations of turbulent reacting flows in a chamber with gaseous ethylene injecting through the porous wall

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Large-eddy simulations were performed to study the turbulent reacting flows in a simulated solid-fuel combustion chamber. The time-dependent axisymmetric compressible conservation equations were solved directly without using subgrid-scale turbulence models. The combustion process considered was a one-step, irreversible, and infinitely fast chemical reaction and the pyrolizing solid fuel was simulated by gaseous ethylene injected through a porous wall for a practical range of fuel blowing velocity encountered in solid-fuel combustion chambers for the first time. The numerical code used the finite-volume technique which involved alternating in time the second-order, explicit MacCormack's and Godunov's methods. Characteristic-based boundary conditions were applied on inflow and outflow boundaries, which allowed outlet boundary conditions to be nonzero gradients and, in turn, a practical length of computational domain to be realized. The effects of combustion on the large-scale unsteady flow structure and the mean flameholder recirculation zone were documented in terms of the density contours, vorticity dynamics, streamlines, mean-velocity vector fields, temperature profiles, flame position, and fuel blowing velocity. A comparison of the distributions of instantaneous and mean mass fractions of reactants shows that the present method appropriately reveals the effects of large-scale turbulent motions on combustion. Furthermore, the present large-eddy simulations have achieved a significant improvement in predicting the mean effective reattachment length over the previous calculations incorporating with turbulence models. The physical insight regarding the decrease of the mean effective reattachment length with combustion was also addressed.