Numerical modelling of pool fires and flame spread
The first objective of this study is to investigate pool fires and improve their modelling by means of the computational fluid dynamics (CFD) approach, in which coupled descriptions of the controlling mechanisms of heat transfer, turbulence, combustion and soot production are included.
In order to improve the accuracy and applicability of existing turbulence and gas radiation models, advanced models including a four-equation turbulence model, a statistical narrow band (SNB) gas radiation model and a correlated-k (CK) gas radiation model are developed and implemented into the CFD code simulation of fires in enclosures (SOFIE) as the first step of this PhD study. The modified code is applied to three pool fire scenarios, i.e. methane, methanol and ethanol pool fires. Simulation results are numerically analysed, and quantitatively compared between the predictions obtained with different models, as well as with experimental data. Results confirm the improvements in accuracy from advanced models – in terms of temperature predictions, up to 59% relative difference for the four-equation turbulence model and 8.8% for the SNB models are found, though more CPU time is required – the four-equation model requires about 10% more than the two-equation models investigated and the SNB model requires 4.8 times of the traditional weighted-sum-of-grey-gas (WSGG) model. As shown in the Methane fire simulations, the CK model yields results very close to the SNB model, while 2.7 times more time consuming, and thus the CK model is not further studied in this work.
After the analysis of pool fires mechanisms and validation of the incorporated models, this research is focused on the numerical and experimental investigation of upward flame spread over solid fuel surfaces. A non-charring pyrolysis model has been developed in SOFIE and is used in this study.