Large Eddy Simulation of Vertical Turbulent Wall Fires

The objective of the present study is to evaluate the ability of wall-resolved large eddy simulations (LES) to accurately simulate wall fires. The boundary layer combustion configuration is a simplified vertical wall flame configuration in which gaseous fuel (propylene) is supplied across a porous wall and the fuel mass flow rate is prescribed. The focus of the study is on the flame-to-wall heat transfer. The LES performance is evaluated via comparisons with a previously developed experimental database.LES simulations are performed using FireFOAM (FireFOAM is an advanced fire modeling software developed by FM Global). The FireFOAM simulations use: a carefully-designed block-structured computational grid; the k-equation eddy viscosity model for turbulence; the Eddy Dissipation Concept (EDC) model for combustion; and the discrete ordinate method for thermal radiation transport. A number of modifications are introduced in the baseline FireFOAM modeling capability: the original turbulent eddy viscosity model is replaced by the wall-adapting local eddy-viscosity model – WALE – that provides correct near-wall behavior; the EDC combustion model is also enhanced to include laminar flame conditions.The wall flame configuration features low Reynolds number conditions and a transitional laminar-to-turbulent combustion regime; while these low Reynolds number conditions are believed to be representative of meter-scale wall fires, they represent a difficult challenge for LES simulations. The simulations are in good qualitative comparison with experimental data; quantitative agreement is fair. The main source of discrepancy is an overestimate of the size of the laminar flame base region and a reduced accuracy of LES combustion and radiation models under laminar-like conditions.