Numerical Simulation of Fire Pressure Effect in Tunnels with Large Unidirectional Longitudinal Slope

After fire happens in a tunnel, the fire pressure will affect the flow of smog in the tunnel. However, in the existing design specifications for road and railway tunnel ventilation, the impact of the fire pressure on fire rescue ventilation has not been considered. In this paper, three-dimensional numerical simulation of fire pressure effect is conducted with Fire Dynamics Simulator (FDS), and the change rules of smoke diffusion field, temperature field, pressure field and visibility are studied in a large highway tunnel with longitudinal slope. It is shown that that in the large longitudinal slope tunnels, only fire effect can result in the flow of the fire smoke. The flow rule is that the smoke is drained out from the high-hole, and at the same time, fresh air is supplied from the low-hole. The fire pressure effect is equal to setting up a series of jet fans on the tunnel where the high-temperature smoke flows by. The action directions of the jet fans are always upward, the result of which promotes fire flow in upward direction and blocks fire flow in downward direction. All the issues mentioned above should be paid more attention in the fire ventilation designs.