Fire Safety Science Digital Archive

The objective of the present study is to examine the feasibility of a Large Eddy Simulation (LES) approach combined with a partially-premixed combustion (PPC) model for simulations of transient combustion events occurring in fuel vapor clouds. The PPC formulation uses: a premixed combustion sub-model based on the filtered reaction progress variable approach; a non-premixed combustion sub-model based on the Eddy Dissipation Concept; and a premixed/non-premixed combustion coupling interface based on the concept of a flame index. The PPC model is implemented into the Fire Dynamics Simulator (FDS) developed by the National Institute of Standards and Technology, USA. Because FDS uses an incompressible flow solver, the present study is restricted to combustion scenarios featuring low Mach numbers (e.g., scenarios with no blast wave). The enhanced FDS modeling capability is evaluated by detailed comparisons with an experimental database previously developed by FM Global Research, USA. The test configuration corresponds to controlled ignition followed by explosive combustion in an enclosure filled with vertically-stratified mixtures of propane in air, both with and without venting, and with and without obstacles. All studied cases develop significant compartment over-pressures; these pressurized combustion cases present a particular challenge to the bulk pressure algorithm in FDS which has robustness and accuracy issues, in particular in vented configurations. The FDS bulk pressure algorithm is modified in the present study in order to allow detailed comparisons between measured and simulated pressure time histories. Overall, the comparison between numerical results and experimental data ranges from fair to good, and confirms the feasibility of a LES treatment of explosive combustion.