“Scaling-up” fire spread on wood cribs to predict a large-scale travelling fire test using CFD

Abstract

Simulation-based approaches for characterising the fire behaviour of travelling fires in large compartments are a potentially valuable complement to experimental studies, providing useful insights on evolving boundary conditions for structural response. They admit the possibility of carrying out systematic parametric studies decoupled from experimental uncertainties, however, sufficiently general models have not been previously demonstrated. Here, we explore the potential for “scaling-up” a “stick-by-stick” CFD model which had been carefully calibrated for the case of an isolated crib, of 2.8 m diameter, to a uniformly distributed fuel bed of extent 4.2 m × 14.0 m located within an open compartment 9 × 15 m in plan, with internal height 2.9 m. The results in terms of the fire spread and burnout predictions are very encouraging, and the heat release rate evolution is also consistent with the experimental value. Furthermore, there is a relatively good match of predicted and measured incident radiant fluxes during the fire spread on the wood cribs. Discrepancies in predicted post fire fluxes and gas phase temperatures can be attributed to the effects of wind on the fire plume (not modelled) and deficiencies in representation of heat transfer from the glowing embers. These factors are expected to have a modest impact on the prediction of fire spread on a horizontally-orientated flat fuel bed, the prime interest of the current work. Thus, the established “numerical simulator” looks to have good potential as a tool to explore and characterise the behaviour of travelling fires subject to different compartment boundary conditions.