非对称V形坡公路隧道火灾烟气蔓延特性研究

Study on Fire Smoke Spreading Characteristics in Asymmetric V-Slope Highway Tunnel

水下隧道常呈两端高中间低的“V”形,火灾风险高,掌握其火灾烟气蔓延特性是开展消防应急响应和疏散救援工作的基础。采用火灾动力学模拟软件(FDS)构建自然通风条件下非对称V形坡隧道火灾模型,研究不同坡度组合下火灾烟气的扩散过程,分析隧道两侧洞口的压力和速度变化。结果表明:变坡点处发生火灾后,非对称V形坡隧道烟气扩散呈现出与单坡隧道相似的多阶段蔓延特性,但高坡度侧烟气蔓延速度较单坡隧道更慢,低坡度侧更快,且烟气稳定回流长度更短;在非对称V形坡隧道烟气扩散过程中,存在着流场重塑、正向动力循环重构、保持稳定3个特征阶段;低坡度侧隧道烟气的最大回流长度、稳定回流长度,以及各自对应时刻,受两侧隧道坡度和坡度差的共同影响,并且存在临界坡度差(4%),当大于该坡度差时,火灾烟气蔓延特征将不再受坡度差的影响。

Underwater tunnels are often high at both ends and low in the middle,showing the"V"shape,with high fire risk.Therefore,mastering the characteristics of fire smoke spreading is the basis of fire emergency response,evacuation and rescue work.The Fire Dynamics Simulation software(FDS)is used to build the asymmetric V-slope tunnel fire model under the condition of natural ventilation,to study the spreading process of fire smoke under different combination of slopes,and to analyze the changes of smoke pressure and velocity at the tunnel portal on both sides of the tunnel.The results show that:after a fire occurs at the slope change point,the smoke spreading in the asym⁃metric V-slope tunnel presents the multi-phase spreading characteristics similar to that in the single-slope tunnel,but the smoke spreading velocity on the high slope side is slower than that in the single slope tunnel,while the smoke spreading velocity on the low slope side is faster,and the steady back-flow length of fire smoke is shorter;In the process of smoke spreading in the asymmetric V-slope tunnel,there exist three characteristic stages:flow field remodeling,forward dynamic cycle reconstruction,and maintaining stability;The maximum back-flow length and the steady back-flow length of the tunnel smoke on the low slope side and their corresponding moments are jointly affected by the tunnel slope gradients on both sides and the gradient difference,and there is a critical gradient difference of 4%.When the gradient difference is greater than 4%,the characteristics of fire smoke spreading will no longer be affected by the gradient difference.