Maximum temperature of ceiling jet flow in longitudinal ventilated tunnel fires with various distances between fire source and cross-passage

Abstract

Maximum temperature rise is an important parameter in tunnel fires. It is noted that classical models of maximum temperature rise in previous studies are limited to single tunnel. However, in real situations, there is cross-passage between two neighboring tunnels. The studies about the effect of distance between fire source and cross-passage on the temperature rise is limited. In this study, numerical simulations on the maximum temperature rise of ceiling jet flow in tunnel fires under longitudinal ventilation with various distances (Lf) between fire source and cross-passage are conducted by using FDS for a cross angle of 30°. Results show that maximum temperature rise decreases with either the increasing of longitudinal ventilation velocity or the decreasing of heat release rate. The cross-passage has an effect on the fire plume flow velocity under the ceiling, which further affects the maximum temperature. For small ventilation velocities (1 m/s and 2 m/s), the maximum temperature rise is much lower than that of a single tunnel without cross-passage, and there is no significant difference between various Lf. For large ventilation velocities (3 m/s and 4 m/s), the maximum temperature rise decreases with the increasing of Lf from 0 to 4.5 m, and for Lf>4.5 m, the maximum temperature rise has no significant change anymore. It is noted that for the large ventilation velocities, the maximum temperature rise of Lf = 0 is close to that of a single tunnel without cross-passage. The effect of cross angle on the maximum temperature rise is also researched which shows that maximum temperature rise increases with the increasing of cross angle. A correlated model is proposed to predict the maximum temperature rise by taken Lf into account.