Modeling of Turbulent Wall Fires
Post-Doc: Ning Ren, PhD; and PhD Students: A. Ojofeitimi, S. Vilfayeau
PhD Students: A. Ojofeitimi, S. Vilfayeau
Wall fires correspond to one of the basic canonical configurations used in fire research. The configuration is representative of a class of problems in which the combustion process occurs in the vicinity of solid walls (the walls may be inert or flammable). Wall flames involve a multi-physics coupling between solid- and gas-phase processes, including buoyancy-driven or momentum-driven, laminar or turbulent flow, fuel-air mixing and combustion, gas-to-solid convective and radiative heat transfer, and (in the case of flammable walls) in-wall thermal degradation (pyrolysis) and release of flammable vapors. An important difficulty in simulations of wall fire configurations is that the characteristic length scales of the problem are small and require fine computational grids (typical values of the flame-wall distance range from one centimeter to a few tens of centimeters).
This research project is aimed at incorporating and evaluating a wall flame heat transfer model into a Computational Fluid Dynamics (CFD) capability called FireFOAM. FireFOAM is a new platform for fire modeling developed by FM Global and is based on the open-source general-purpose CFD software package called OpenFOAM. FireFOAM features state-of-the-art computer science, mesh generation and physical modeling capabilities, including an object-oriented C++ environment, an unstructured grid capability, a compressible flow formulation, advanced large eddy simulation (LES) models and multi-physics models.
Current work is focused on simulating a simplified wall flame configuration in which the fuel is supplied at a constant uniform rate through an array of porous burners. This configuration was previously studied experimentally at FM Global by de Ris and co-workers; the prescribed fuel mass flow rate conditions are viewed as a fundamental building block in a wall fire modeling strategy. The wall flame configuration features low Reynolds number conditions and a transitional laminar-to-turbulent combustion regime. While these low Reynolds number conditions are representative of meter-scale wall fires, they correspond to 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 lack of accuracy of LES combustion and radiation models under laminar-like conditions. Current work is focused on over-coming these difficulties.
Dr. Ning Ren is a Research Associate in the Department of Fire Protection Engineering. For further information about his research, he can be contacted at: