Numerical simulations of full-scale enclosure fires in a small compartment with natural roof ventilation

Numerical simulation results are presented of full-scale fire tests in a small compartment (3×3.6×2.3 m). A range of total fire heat release rates (330, 440 and 550 kW), fire source areas (0.3×0.3 m and 0.6×0.6 m) and ventilation roof opening areas (1.45×1, 0.75×1 and 0.5×1 m), is covered. Both two-zone model calculations and field model simulations are considered. For the different configurations, profiles of mean temperatures and temperature fluctuations are reported. Furthermore, the mean flow field and temperature field in the compartment are extensively discussed, providing insight in the entrainment and mixing phenomena in the plume in the compartment. The smoke layer depth is determined for all configurations. The computational fluid dynamics (CFD) simulations agree well with experimental observations. The total fire heat release rate value has the strongest influence on the hot smoke layer average temperature rise, while the influence of the fire source area and the roof opening is smaller. The hot smoke layer depth, determined from the mean temperatures, is hardly influenced by the total fire heat release rate. The roof opening also only has a moderate influence in the range considered. The largest impact on the layer depth is due to the fire source area with an increase of the depth as the fire source area increases. Correlations are given for the average hot smoke layer temperature rise and the total smoke mass flow rate out of the compartment, as a function of the different parameters mentioned. A study of the buoyancy reference velocity leads to the verification of a formula to estimate the total smoke mass flow rate out of the compartment. The performance of different entrainment models in zone model calculations is discussed in relation to the obtained CFD results.