Effect of bifurcation angle and fire location on smoke temperature profile in longitudinal ventilated bifurcated tunnel fires

The maximum ceiling temperature and longitudinal temperature distribution were investigated in bifurcated tunnels with different bifurcation angles under longitudinal ventilation. A series of experiments were carried out in a 1:10 small-scale bifurcated tunnel with a bifurcation angle of 60 degrees, considering different longitudinal fire locations. Furthermore, 44 cases including 2 fire locations with bifurcation angles between 20 degrees similar to 90 degrees were simulated by FDS. The results indicated that: (1) The longitudinal fire location would affect the maximum temperature rise in the bifurcated tunnel. When the fire was in the bifurcated zone, the maximum temperature was lower than that in the non-bifurcated zone under a same condition. (2) The bifurcation angle had little effect on the maximum ceiling temperature. (3) The longitudinal temperature distribution of the main tunnel in the downstream from the fire source was independent of the bifurcation angle, while the attenuation rate of longitudinal temperature of the branch tunnel increased with the increasing of bifurcation angle. In addition, prediction models of the maximum ceiling temperature rise and the longitudinal temperature distribution in the main tunnel and branch tunnel were proposed, which could well predict the smoke temperature profile in T-shaped bifurcated tunnels with bifurcation angles between 20 degrees and 90 degrees under the dimensionless ventilation velocity greater than 0.19.