Effects of tunnel aspect ratio on the temperature profile near fire field in tunnel under natural ventilation: a numerical investigation and analysis

The ceiling temperature distribution near fire field is a critical characteristic parameter for assessing the risk and dynamic characteristics of a tunnel fire. Nevertheless, the temperature of the ceiling jet propelled by the weak and strong has not been studied in relation to the tunnel aspect ratio in previous research. In this study, a series of numerical simulations are performed to investigate the vertical and transverse temperature distribution under the ceiling, with the heat release rate and tunnel aspect ratios being adjusted. It is found that there is an obvious difference between the vertical temperature variation above the fire source and other positions, as the varying tunnel aspect ratio. Significant differences in the transverse temperature decay behavior of the ceiling jet generated by strong and weak plumes are found. Furthermore, a quantified analysis of the transverse temperature distribution for the faint and strong plume is performed. As a result, two empirical models of transverse temperature distribution were postulated for the weak and strong plumes, respectively. The current study results lead to a more in-depth understanding of the fire characteristics of the tunnel with large aspect ratio, as well as to the optimization of fire detection and emergency ventilation.