Flame behavior and maximum ceiling temperature in traffic merging section tunnel fires: An experimental study and engineering modelling methodology

Abstract

In recent years, the construction of bifurcated tunnels has increased in cities to facilitate the interconnection of urban transportation systems but posing significant fire risks at the same time. In this study, the effect of the ventilation condition and heat release rate (HRR) on flame behavior and temperature distribution in tunnel traffic merging section is studied with scale-model experiments. Results show that under confluent ventilation, the flame tilts towards both longitudinal and transverse directions, causing the location of the maximum ceiling temperature rise to deviate from the center-axis. Using the centerline temperature as the global maximum ceiling temperature will result in around 5 % systematic error. The increasing confluent ratio has a limited impact on the longitudinal flame deflection, whereas it induces a significant variation in the transverse deflection angle. The maximum ceiling temperature rise exhibits an initial increase followed by a subsequent decrease, accordingly. A virtual ventilation vector and a non-uniform inflow correction function are proposed to correlate the 3-D plume behaviour with the complex confluent flow field. Finally, a semi-empirical equation to evaluate the maximum ceiling temperature rise considering the multi-dimensional flow field is proposed and validated with existing test data. This work contributes to a deeper understanding of the classical tunnel fire dynamic theory and provides a novel engineering modelling methodology for the plume behavior in bifurcated tunnel fire scenarios.