CFD Based Simulation Analysis On Research Of Smoke Features Of Vehicle Fire In Large Cross-section Road Tunnel

Recent incidents however have drawn widespread attention to the risks of fires in road and rail tunnels (e.g. King's Cross, Channel Tunnel, Mont Blanc, Tauern, Gotthard). The incidents have resulted in casualties as well as large direct and indirect economic damage.The control of smoke flow during a tunnel fire is often an important part of fire safety measure. Critical velocity is also an important factor to discuss the ventilation and the smoke flow.CFD(Computational Fluid Dynamics) simulations are increasingly used to estimate the effects of fires in tunnels. However, little work has been done to analysis the fire characteristics of large cross-section road tunnel. The objective of this paper was to discuss the smoke distribution feature in large cross-section road tunnel fires and to get the critical velocity of the road tunnel fires, adopting the CFD software of FDS(Fire Dynamic Simulator) which was developed by NIST. Firstly, the simulation model was constructed according to Shanghai Yangzi road tunnel with diameter of 15 meter. Some other cross-section road tunnel were also discussed. Secondly, considering different scenarios of longitudinal ventilation velocity, the spread velocity and scope of smoke were simulated and analyzed respectively in case of a 20 MW fire. Thirdly, in order to get of the critical velocity of longitudinal ventilation, a series of other fire scene was simulated. On the basis of simulation results, the calculating method of the critical velocity of longitudinal ventilation was set up. Fourthly, performance-based critical velocity was attempted to put forward and analyzed. In according with the simulated smoke distribution feature, the ventilation scheme of large cross-section road tunnel in fire emergency was also suggested.The simulation data demonstrated that specifying a critical velocity of ventilation was helpful to prevent back layering of smoke during a tunnel fire. Hence, it was very important for smoke management of large cross-section road tunnel. In order to find cost-effective methods to upgrade fire safety in existing tunnels or tunnels to be built, the performance-based method should be used to calculate the critical velocity of ventilation, including the impact of tunnel physical characteristics and tunnel ventilation system.In the finality, the problems requiring further studies are simply discussed.