A model providing detailed description of the trajectory and the internal composition of firefighting hose streams in air quiescent conditions is presented. The proposed model is based on a 1D Eulerian approach over the stream’s trajectory path, allowing for simultaneous multi-phase description of the fire stream (water-core phase, spray phase and air phase), including air entrainment, jet break-up, spray generation and multi-dispersion. A series of 6 large nozzle streams were studied experimentally. Predicted and measured stream trajectories were compared using Mean Absolute Percentage Deviation (MAPD) and Maximum Absolute Error (MAE) performance criteria. Among the 6 tests, a MAPD peak value of 4.6% and MAE of 17 cm were found, showing a good agreement with experimental measurements. Internal composition of a fire stream was studied numerically. Results suggested a predominance of water-core phase initially, accounting 50% of the fire stream’s mass just before its break-up. In contrast, an increasingly leading role of air phase through the trajectory path was found, accounting 90% of the fire stream’s mass at ground level. In addition, results suggested that 49% of the injected water flow was evacuated from the stream consequence of the progressive generation of the spray along the trajectory.

A Model for Predicting the Trajectory and Structure of Firefighting Hose Streams

Abstract The feasibility of coupled computational fluid dynamics (CFD) and finite element (FE) simulations to aid the planning of fire intervention tactics and the effectiveness of structural cooling during firefighting were investigated. Water sprays, generated using fire monitors, were characterized using bucket tests and the results were used for calibrating the CFD spray model. The cooling ability of the sprays was measured experimentally by applying them onto a fire exposed steel beam. The experimental results showed that water application produces a sudden drop in steel temperatures and after 10–15 s, no significant further reduction in temperature was observed. The CFD-FE coupling was performed using the adiabatic surface temperature method, extended here to include the cooling by water droplets. The coupled CFD-FE model was validated using the experimental data and applied to simulate the intervention to a developing warehouse fire, showing how an attempt to cool the structure reduces the temperatures but does not stall the fire-spread. In fact, the intervention -induced vapor generation was found to enhance the flow of hot gases and accelerate the fire-spread if the water resources are inadequate. Thermal and stress analyses of the cooled and uncooled truss beams were performed, showing how the spray cooling halted the truss mid-span deformation. 

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Hao-Yu Dai

Papers

Applying large-scale PIV to water monitor discharge experiment