隧道挡风板对竖井自然排烟效率的影响研究

Study on the effect of tunnel barge boards on the smoke extraction efficiency of the shaft with natural ventilation

通过数值模拟研究了隧道内挡风板的设置对竖井自然排烟系统效率的影响,探讨了不同火源热释放速率与不同挡风板安装参数(挡风板高度、挡风板与竖井距离)下隧道火灾的烟气温度分布规律、流动规律及竖井自然排烟系统排烟效率。采用N系数法确定了烟气层与冷空气的界面,用于判断是否发生烟气层吸穿现象。结果表明,与无挡风板的工况相比,设置挡风板后,竖井排烟效率提升显著。设置挡风板对向下游方向运动的火灾高温烟气产生了一定的阻滞作用,使高温烟气在竖井下方蓄积,在一定程度上避免了竖井自然排烟系统出现烟气层吸穿现象。设置挡风板后,竖井的排烟效率随挡风板高度增加而增加,而挡风板与竖井间距离的变化对竖井排烟效率的影响较为有限。对于相同的火源热释放速率,竖井排烟效率与挡风板高度在一定范围内几乎成线性变化。建立了排烟效率与无量纲挡风板高度及无量纲火源热释放速率之间的经验公式,可对不同挡风板高度与热释放速率下的竖井自然排烟效率进行预测。

In this paper,the influence of the barge boards in the tunnel on the efficiency of the natural ventilation system with the vertical shaft is studied by numerical simulations.The characteristic of fire smoke temperature distribution,the characteristic of the velocity field of the smoke flow,and the efficiency of smoke removal of the shaft are discussed under different heat release rates of fire sources and different arrangements of the barge boards(different heights of the barge boards and different distances between the barge boards and shaft).The N coefficient method is adopted to determine the interface between the smoke layer and the ambient cold air,which is used to judge whether the plug-holing phenomenon occurs.The results show that,compared with the scenarios without barge boards,the smoke removal efficiency of the naturally ventilated shaft is significantly improved when there are barge boards.The blocking effect induced by the barge boards can impede the movement of fire-induced smoke flowing to the downstream direction,which can lead to the accumulation of smoke below the naturally ventilated shaft.The phenomenon of plug-holing of the smoke layer is avoided to a certain extent.The smoke removal efficiency of the shaft increases with increasing the height of the barge boards.However,the change of the distance between the barge boards and the shaft has little effect on the efficiency of the smoke removal.For the same heat release rate,the relationship between the smoke removal efficiency and the height of the barge boards is almost linear in a certain range.The empirical formula among the smoke removal efficiency,the dimensionless height of the barge boards,and the dimensionless heat release rate of the fire source is established,which can predict the smoke removal efficiency for the naturally ventilated shaft with different heat release rates and barge boards heights.