Computational Fluid Dynamics Simulations of Water Spray Interaction with a Fire-Driven Flow in a Confined and a Mechanically Ventilated Enclosure

International audienceThe paper presents a detailed numerical study on the interaction between two water sprays and a fire-driven flow in a confined and mechanically ventilated enclosure of 4.9 m × 8.7 m × 3.9 m (height). The fire source is a 1.2 m × 1.2 m × 0.3 m propane burner, which is positioned in a corner and generates a well-controlled heat source of about 290 kW. The mechanical ventilation consists mainly of an inlet and an extraction ductdelivering each a flow rate of about 2500 m3/h. The two nozzles are mounted at 0.9 m below the ceiling and deliver a total flow rate of 107 l/min with a volume-median droplet diameter of about 470 μm. The CFD simulations carried out with the Fire Dynamics Simulator (FDS, 6.7.0) show a good agreement with the experimentally measured room pressure profile. More particularly, the under-pressure peak which occurs upon activation of the water spray system is well-predicted (i.e., -993 Pa in the experiments Vs -832 Pa in the simulations) provided that a sufficiently computational droplet injection rate is prescribed (Np = 80,000 droplets per second). As observed in the experiments, the CFD simulations show that the watersprays cause a relatively uniform species and temperature distribution from floor to ceiling. Thermal stratification is sustained though, especially in the region between the nozzles and the ceiling. Finally, an energy balance analysis shows that the experimentally estimated fraction of heat absorbed by the water (i.e., 65%) is higher than the one calculated in CFD (i.e., 40%)