Influence of Vent Location on Efficiency of Smoke Extraction in Tunnel Fire

To study the influence of smoke vent location on smoke extraction efficiency for semi-transversal smoke control system in long tunnel, a 1∶20 reduced-scale tunnel model was built on the basis of Memorial Tunnel. The model has a dimension of 42.7 m × 0.45 m × 0.23 m, with two gradients of 0% and 3.2%. A series of fire experiments were conducted in the tunnel model with the fire source of pool fire (methanol). Meanwhile, three different scenarios were simulated using Fire Dynamics Simulator (FDS 6.0.1), in which two smoke vents are located on the left side, the right side, or both sides of fire source. By comparing the numerical simulation and experimental results, the following conclusions are made: (1) In the horizontal tunnel (0% gradient), the smoke layer distributes symmetrically for the smoke vents symmetrically located on both sides of fire source. Smoke extraction efficiency in this scenario reaches the maximum, with increases of 10.22%–13.58% and 7.66%–16.84% in contrast to the other two cases with smoke vents on the left and right sides respectively. These two cases show no significant difference in smoke extraction efficiency although the length of smoke layer is prolonged; (2) In the tunnel with a gradient of 3.2%, smoke layer asymmetrically distributes on both sides of fire source and more smoke spreads to the uphill side. Smoke extraction efficiency is the lowest for smoke vents on the left side of fire source (downhill side), it increases by 33.9%–39.6% for vents symmetrically located on both sides of fire source, and reaches the maximum for vents on the right side of fire source (uphill side), increasing by 40.5%–51.6% compared with that with the vents on the left side; (3) The influence of smoke vent location on smoke extraction efficiency in the inclined tunnel is more significant than that in horizontal tunnel and the degree of influence reduces with the increase of smoke extraction volume.