Numerical investigation on the maximum ceiling temperature and longitudinal decay in a sealing tunnel fire

Sealing the tunnel entrance is one of tactic for railway tunnel firefighting. In order to understand the effect of tunnel entrance sealing ratio on fire behavior, Computational Fluid Dynamics (CFD) is used to simulate tunnel fire with different heat release rates and sealing ratios varied from 0% to 100%. Both the maximum temperature and the temperature distributions along the tunnel ceiling were calculated by the empirical model and compared with previous experimental data. Results show that the ceiling temperature increases with sealing ratio due to the heat accumulation inside the tunnel when the heat release rate is relatively small. Moreover, the longitudinal ceiling temperature decreases with the increase of the tunnel entrance sealing ratio at initial stage and then tends to stability due to less oxygen supply when the heat release rate is relatively large. The maximum temperature along the tunnel ceiling decays exponentially. The correlations determining the maximum temperature and temperature decay beneath the tunnel ceiling are proposed to modify the current model taking the tunnel entrance sealing ratio into account. The predictions agree well with the experimental and measured data by the modified equations of this paper.