Numerical simulation of turbulent flame–wall quenching using a coherent flame model

Abstract

Flame quenching by fine mesh is one of the oldest known methods for mitigating flame propagation. Sir Humphry Davy pioneered the study of flame–wall quenching while developing the mining safety lamp. Installing a quenching mesh around the equipment is an effective preventive technique against hazardous flame propagation. Quenching of flame at the wall is due to the coupled thermo physical process involving heat transfer, flame stretch and preferential diffusion. While laminar flame–wall quenching has been extensively studied both theoretically and numerically, the reported studies of turbulent flame–wall interactions are limited to some Direct Numerical Simulations (DNS), which have subsequently led to improvement of models for predicting flame characteristics in the vicinity of the wall.Large Eddy Simulation (LES) of turbulent flows is considered as a powerful tool to predict the occurrence of instabilities due to heat release, hydrodynamic flow fields and acoustic waves. It provides a better description of turbulent–combustion interaction than the classical Reynolds Averaged Navier Stokes techniques (RANS). In the present study, the single mesh quenching of turbulent flame deflagration is investigated in stoichiometric methane–air mixture, which is equi-diffusive with unit Lewis number. It is well known that flame stretch and preferential diffusion has negligible influence in flame quenching for equi-diffusive flames. Therefore a unity Lewis number flamelet formulation can be used for simulating the turbulent combustion process within the premixed flamelet regime.In the present study, LES predictions are performed using the OpenFOAM CFD toolbox solver. The Coherent Flame Model (CFM) in the LES context as proposed by Richard et al. (2007) is implemented for modeling flame deflagration. During the flame/wall interactions, enthalpy loss through the wall affects the flamelet speed, flamelet annihilation and flame propagation; and the decrease in turbulence scales near the wall affects turbulent diffusion and flame strain. These flame–wall interactions are accounted for through extending the closures proposed by Bruneaux, Poinsot, and Ferziger (1997) for the CFM–RANS model to the LES context. Preliminary testing has demonstrated good potential of the modified CFM to capture the quenching effect of the wall.