Large Eddy Simulation of the Backdraft Phenomenon and Its Mitigation in Compartment Fires with Different Opening Geometries

Abstract

A sub-grid scale model for partially premixed combustion has been implemented into an existing LES code and applied to simulate turbulent deflagration in backdraft and its mitigation by watermist in a scaled-compartment with different vent geometries. The model is based on the coupling of independent approaches for non-premixed and premixed turbulent combustion, while the flame index concept was used to separate the two different combustion regimes. Simulations were conducted for the reduced scale tests of Weng and Fan (2002). Reasonable agreements have been obtained for species concentrations, total mass outflow and inflow rates, maximum pressure, and likelihood of the occurrence of the fireball outside the container. The numerical study has highlighted the mitigation effect of watermist by reducing the laminar burning velocity of the mixture and the influence of the end opening geometries on the occurrence of backdraft.

Keywords:

• Backdraft
• Compartment fires
• Large eddy simulation
• Mitigation
• Watermist

This work is funded by the European Commission Framework 5 Research Programme through the FIRENET project. The authors gratefully acknowledge the use of FDS code from NIST. The calculation of the Steady State Flamelets were carried out using the Flame Master code provided by Dr. Pitsch from the Center for Turbulence Research at Stanford University.