Influences of longitudinal ventilation and two same of obstacles placed upstream and downstream of the fire source on gas temperature distribution in a tunnel

In case of tunnel fire, vehicles can be blocked both upstream and downstream of the fire source. This paper presents a numerical study on influences of longitudinal ventilation and two same of obstacles placed upstream and downstream of the fire source on gas temperature distribution in a tunnel. The heat release rate, ventilation velocity and blockage ratio are varied. Results show that for a given ventilation velocity, as the blockage ratio increases, the inclination of fire plume gradually changes from the downstream to the upstream and the downstream smoke spread distance below the ceiling decreases. The Coanda effect (which refers to the adhesion of fluid on a convex surface) and the velocity vector field are introduced to explain the attachment of fire plume to the upstream obstacle. As the blockage ratio increases, the gas temperatures in the upstream of the fire source increase, while the gas temperatures in the downstream of the fire source decrease. The maximum temperature tends to decrease with increasing ventilation velocity. The effect of blockage ratio on maximum temperature is obvious for small ventilation velocities, while it becomes insignificant for large velocities. Then the maximum temperature model concerning the block effect and ventilation velocity are proposed.