Large-eddy simulation of methanol pool fires using an accelerated stochastic fields method

Large-eddy simulation with transported probability density function (t-PDF) method for modelling pool fires is presented. The PDF method that is used here is based on the Eulerian stochastic fields method (SF), and is accelerated with chemistry coordinate mapping (CCM) technique. SF-CCM for large-eddy simulation is formulated and applied to simulate methanol pool fires with various pool sizes for the first time. The model includes finite rate chemistry effects with detailed chemistry of the methanol combustion. The simulation results agree well with experiments in terms of the averaged flame height and the maximum ceiling temperature. More important is the capability of the current approach in reproducing the dynamic characteristics of the fire plume. Especially, the intermittent behaviour of pool fires and its response to the effects of the pool size are predicted, accurately. The key factor to success is the capability of the method in handling multiple modes of combustion in both premixed and non-premixed mixtures. It is shown that a pool fire involves the local and global extinction which is mainly due to the large entrainment of the fresh and cold ambient air to the base of fire plume. It is shown that the quenching and re-ignition are key processes in the understanding the dynamic behaviour of pool fires.