挡风墙对风区隧道火灾排烟效果的影响研究

Effect of windshield wall on smoke exhaust of tunnel fire in windy area

烟气是隧道火灾中的最致命因素。针对处于风区的隧道受环境风影响,火灾烟气无法有效排出导致隧道内热量积聚和人员受困的问题,建议在风区隧道出口设置合理尺寸的挡风墙。以标准的2车道公路隧道为例,基于对公路隧道火灾载荷的调研,借助FDS(Fire Dynamics Simulator)软件建立典型的2车道公路隧道火灾模型,考虑风区10,20和30 m/s 3种横风速度,分别讨论有无挡风墙时的隧道内火灾烟气运动情况。无挡风墙时,横风会将烟气封堵在隧道内,造成隧道内热量的积聚,同时,隧道下部空间被烟气侵蚀,对人员逃生和救援工作产生不利的影响。进一步探讨不同宽度和高度的挡风墙对隧道内火灾烟气运动、隧道顶部温度、能见度及烟气层高度参数的影响,从而确定适合风区2车道公路隧道的最佳挡风墙尺寸。研究结果表明,隧道出口设置挡风墙可以有效促进风区隧道火灾烟气的排出,且能够大大降低隧道顶部温度。这是由于风流经过挡风墙时发生边界层分离,挡风墙内部形成负压驱使火灾烟气从隧道排出。当横风速度较大时,烟气倾向于全部从风区一侧排出,非风区一侧形成完全干净的空间,此时人员逃生和灭火救援可以从非风区侧进行。此外,挡风墙的尺寸并非越大越好,基于3个隧道火灾安全疏散指标,提出了优化的风区2车道公路隧道的挡风墙尺寸为4 m(宽)×8 m(高)。

Smoke is the most fatal factor in tunnel fires.It is suggested to set up a windshield wall with reasonable size at the end of the tunnel in wind area to address the issue of heat accumulation and personnel trapped due to the inability of smoke exhaust under the influence of crosswind.Taking the standard two-lane highway tunnel as an example,and based on the research of fire heat release rate in tunnel fires,a series of numerical simulations of the typical two-lane road tunnel fire were conducted by FDS(Fire Dynamics Simulator)software,considering three wind speeds of 10 m/s,20 m/s,and 30 m/s.The movement of hot smoke in tunnels with and without windshield was discussed separately.It was found that the crosswind would block the overflow of the hot smoke,resulting in the accumulation of heat in the tunnel for without windshield conditions.In addition,the lower space of the tunnel would be polluted by the smoke,which was not conducive to escape and rescue.Furtherly,the smoke movement,temperature field,visibility,and smoke layer height under the influence of different wall widths and heights were discussed to determine the optimal size of windshield wall for two-lane road tunnels in the windy area.The results show that the windshield can effectively promote the smoke exhaust,and the ceiling temperature is obviously reduced.The reason is that the boundary layer separation occurs when the airflow passes through the windshield.The negative pressure zone is formed between the windshield on both sides,which drives smoke to discharge from tunnels.When the crosswind speed is relatively large,hot smoke tends to be discharged from the tunnel side in windy area,while a completely clean space is formed at the other tunnel side,so that personnel escape and firefighting can be carried out from the clear area.Besides,a large windshield wall does not mean a good effect of smoke exhaust.Based on the safety evacuation index of tunnel fires,the optimized windshield wall size of 4 m(width)×8 m(height)for two-lane road tunnels in windy area is proposed.