James White, Sebastien Vilfayeau, Andre Marshall, Arnaud Trouve,
This work seeks to support the validation of large eddy simulation (LES) models used to simulate the response of fires to the activation of a suppression system. The emphasis in the present study is on the prediction of flame weakening and extinction when the fire is exposed to gaseous agents, and the prevention of spurious reignition within a fast chemistry (`mixed-is-burned') combustion model. The experimental configuration generates turbulent, statistically two-dimensional, buoyancy- driven, methane diffusion flames within a controlled co-flowing oxidizer. The co-flowing oxidizer allows for the supply of a mixture of air and nitrogen, including conditions for which oxygen-dilution in the oxidizer leads to global flame extinction. Detailed measurements to support model validation include local temperature profiles, global radiative loss fraction, global combustion efficiency, and the limiting oxygen index. The present study evaluates the performance of critical-flame-temperature-based extinction and reignition models using the Fire Dynamics Simulator, an open-source LES-based fire dynamics solver. Alternate reaction schemes are explored, each offering a unique treatment of reignition, but all subject to the same extinction criterion. Comparisons between simulated results and experimental measurements provide a suitable test bed to evaluate the capability of these models to accurately describe flame extinction. Of the presently considered schemes, those that include provisions to prevent spurious reignition are able to accurately predict extinction performance, whereas a baseline scheme lacking explicit reignition treatment fails to predict extinction in the present configuration.
Fire Safety Journal
Large Eddy Simulation, Fast Chemistry, Extinction, Reignition, Fire Dynamics Simulator