A numerical study on upstream maximum temperature in inclined urban road tunnel fires

Abstract

Numerical simulations were carried out to study the smoke behaviors induced by fires in inclined tunnels with different slopes and the upstream maximum temperatures along the tunnel centerline were specifically focused. The simulation results show that the longitudinal centerline peak temperature occurs at the downstream region of fire source rather than right above the fire source. Two typical behaviors were found during the quasi-steady state: the upstream smoke layer interface is almost parallel to horizontal level while the downstream smoke layer interface is parallel to the inclined tunnel ceiling. The upstream maximum temperature under the ceiling remain approximately constant near the fire sources and then drop progressively with increasing distance to fire source due to the existence of vortexes, which is fairly different from the downstream maximum temperature distribution. Hence, an empirical correlation is developed by taking into account the tunnel slope, heat release rate and the upstream maximum temperature and using dimensional analysis. The correlation indicates that the dimensionless upstream maximum temperature decreases as the distance from fire source increases and it is proportional to 0.56 power of the dimensionless heat release rate and its relationship with tunnel slope is nonlinear and non-monotonous.