Numerical investigation of the temperature characteristics beneath the ceiling driven by a strong plume in a longitudinal ventilated tunnel

Previous studies have mainly focused on the situation that the tunnel's continuous flame region was lower than the ceiling height. For tunnels with longitudinal ventilation, the temperature characteristics of strong fire plumes are still unclear. In this paper, the maximum temperature rise beneath the ceiling for strong fire plume conditions in a small-scale tunnel is studied using fire dynamics simulator. Results show that when the effective height (the distance from the burner surface to the ceiling of the tunnel) is 0.65 m, the maximum temperature rise beneath the ceiling in this work shows a good correlation with Li's model and Kurioka's model. However, as the effective height decreases to 0.55 and 0.50 m, the maximum temperature rise would be significantly lower than the previous model. Therefore, a dimensionless coefficient is introduced to modify the maximum temperature rise model for a strong fire plume, which involves the effective height coefficient, heat release rate, and longitudinal ventilation. A calculation model for the maximum temperature rise beneath the tunnel ceiling in the condition of strong fire plumes is established. The temperature attenuation data along the tunnel are given by statistics. The relationship between the dimensionless temperature rise and the dimensionless position parameter is established, and a unified model under various heat release rates is obtained.