Study on the Smoke Diffusion and Maximum Ceiling Gas Temperature in an Inclined Tunnel With the Upper or Lower Portal Sealed

A series of numerical simulations and small-scale experiments have been conducted to study the smoke diffusion and maximum ceiling gas temperature in an inclined tunnel with the upper or lower portal sealed. A total of 60 simulation cases and 4 experimental tests were conducted, and different sealing conditions, heat release rates, and tunnel slopes were taken as the main variables. The results show that the sealing condition and tunnel slope have a significant impact on the smoke diffusion and flame shape. When the lower portal is sealed, smoke moves to the opening along the tunnel ceiling, and there is an obvious shear phenomenon between the smoke layer and the cold air layer. When the upper portal is sealed, the smoke layer interface in the downhill direction is almost parallel to the horizontal line, and a larger slope means a longer time taken to spill out of the tunnel. In horizontal tunnels, the maximum ceiling temperature in the tunnel with two portals opened is larger than that in the one-portal-sealed tunnel. Tunnel slope has little effect on the maximum temperature rise for the inclined tunnel with the lower portal sealed. However, in the tunnel with the upper portal sealed, the maximum temperature rise increases with the tunnel slope, and the growth is relatively linear. For inclined tunnels, a comprehensive empirical formula is finally established to estimate the maximum ceiling temperature, taking sealing condition, heat release rate, and tunnel slope into consideration.