An experimental investigation of burning rate and flame geometric parameters of tunnel fires under canyon cross wind and longitudinal ventilation

In this study, a series of small-scale experiments were carried out to investigate the variations of burning rate and flame shape of highway tunnel fires in alpine gorge areas with canyon cross wind and longitudinal ventilation. The canyon cross wind was set outside one of the tunnel portals, and the longitudinal ventilation was set at the other. The velocities of the canyon cross wind and longitudinal ventilation, and the longitudinal fire position in the tunnel were varied in this study. The experimental results show that the burning rate increases with increasing the velocity of the overall airflow in the tunnel, which is the combination of the canyon cross wind and longitudinal ventilation. For each velocity of the canyon cross wind, there is a corresponding longitudinal ventilation velocity making the flame burn vertically upward, which is proportional to the canyon cross wind velocity. Based on this relationship, the velocity of overall airflow in the tunnel can be obtained under various wind conditions. In the case that the airflow in the tunnel is dominated by the longitudinal ventilation, the prediction model of flame tilt angle with the canyon cross wind and longitudinal ventilation velocities is proposed. The dimensionless flame height can also be fairly well fitted by power function with the velocity of the overall airflow in the tunnel.