低气压对竖井自然排烟隧道内火灾烟气层的影响研究

Effect of Reduced Ambient Pressure on the Smoke Layer of Fire in Shaft Natural Exhaust Tunnel

高海拔地区低气压环境特性对隧道内火灾烟气的运动特性和温度分布产生的影响不容忽视。为研究环境压力对竖井自然排烟隧道内火灾烟气热分层及温度纵向分布规律的影响,通过对环境压力为50~101 kPa的全尺寸公路隧道火灾进行数值模拟,首先探究隧道内火灾烟气层的层化强度随环境压力的变化特性;其次分析低气压下火灾烟气的运动及温度分布差异;最后研究隧道火源段内火灾烟气温度纵向衰减的分布规律。结果表明:相比较标准大气压,在环境压力降低的情况下,隧道内火灾烟气温度升高,火灾烟气层的层化强度增强;低压环境下隧道内涡旋结构区域面积减小,火灾烟气层的输运变得更加稳定;隧道火源段内火灾烟气温度的纵向衰减分布规律服从指数函数,其衰减系数随环境压力的降低而增加。

The effects of reduced ambient pressure at high altitude on the movement characteristics and temperature distribution of smoke in tunnel fire cannot be ignored.In order to study the influence of ambient pressure on smoke thermal stratification and temperature longitudinal distribution in a tunnel with shaft natural exhaust,we conducted numerical simulations for a full-size road tunnel with ambient pressures ranging from 50 kPa to 101 kPa.Firstly,we investigated the variation of firesmoke stratification intensity under different ambient pressure,and then analyzed the difference of firesmoke movement and temperature distribution under reduced ambient pressure.Finally,the variation of smoke temperature decay in the fire source section was obtained.This study shows that compared to standard atmospheric pressure,the temperature of the fire smoke inside the tunnel increases and the stratification intensity of the smoke improves when the ambient pressure decreases.Under the reduced ambient pressure,the area of the vortex structure inside the tunnel is smaller and the transport of the smoke layer is steadier.Meanwhile,the longitudinal temperature decay in the fire section follows an exponential function distribution and the decay coefficient increases as the ambient pressure decreases.