基于FDS的公路隧道火灾通风环境研究

Trace and examination of the ventilation environment of the highway tunnel fire based on the software known as FDS

隧道发生火灾时,研究隧道内的烟气蔓延特性,选择合适的纵向风速,确定最佳的通风控烟方案,具有重要的研究价值。利用计算流体力学数值模拟技术,选用FDS软件以秦岭Ⅰ号隧道(上行线)为对象建立局部隧道模型,模拟最大热释放率为30 MW的火灾,设计4种不同工况进行模拟计算。模拟了不同纵向风状态下的隧道火灾,观测烟气扩散规律,确定临界风速为3. 6 m/s;在无纵向风、较小纵向风和临界风速状态下,分析了隧道内温度场和烟气场的变化规律,得出其对人员疏散和火灾救援的影响;在通风井通风排烟模式下,模拟了排风道在不同风速状态下的排烟效果,确定最佳排烟风速为4. 6 m/s;射流风机开启前,隧道内风速的大小和方向对隧道内火灾温度场和烟气场的影响很小。给出了适用于秦岭Ⅰ号隧道(上行线)各工况的通风控制策略,也可为同类型特长隧道的火灾通风设计提供参考。

In this paper,a numerical simulation method has been adopted based on Zhongnanshan Tunnel of Qinling(upstream line),Shaanxi,in its relation to the temperature field,the smoke distribution need and the fire spreading regularity in the tunnel.When the tunnel is supposed on fire,it would be of great need to study and clarify the smoke spread characteristic features in the tunnel,choose an appropriate longitudinal wind speed and determine the best available ventilation and smoke control scheme to work out proper measures for fire control,personnel and vehicle evacuation.For the above said purpose,we have established a local tunnel model for the 5 possible fire reducing and control conditions in the tunnel.The research results we have worked out can be stated as follows:The longitudinal wind of different strengths should be set up to observe and trace the diffusion situations of the smoke movement in the tunnel with the critical wind velocity of the fire being 3.6 m/s by using the well-known FDS software and the maximum heat or thermos releasing rate of the simulated fire being 30 MW under the above said 5 working conditions.For instance,under the condition with no longitudinal wind,or minor longitudinal wind and critical wind velocity,it may be suggested that,in the early evacuation stage,ventilation is supposed to be done with smaller longitudinal wind and then followed with the variation law to take the critical wind speed after evacuation so as to affect the temperature and smoke field.Analyzing the smoke exhaust effect of the ventilation shaft exhaust duct under the different exhaust velocities,the optimalized exhaust velocity should not be set over or beyond4.6 m/s.At this juncture,if the jet fan is turned on for 90 s,the dynamic change of the natural wind velocity and direction in the tunnel should have little effect on the fire size.Therefore,it is recommended to apply s critical wind velocity in correspondence with from big scale fire to small scale one.And,then,careful analysis of such parameters as temperature and smoke visibility in the simulation results may help to ensure the feasibility and authenticity of the numerical simulation method.Thus,it can be seen that the research results we have worked out should be in a position to provide a reference to formulating emergency plans for the fire prevention and disaster relief of Qinling Zhongnanshan Tunnel in the fire ventilation construction of the same type of tunnels.