导热和绝热隧道顶棚近壁面火灾烟气层特性  

Characteristics of Smoke Layer Behavior Beneath Heat-Conducting Ceilings and Adiabatic Tunnel Ceilings

作　　者：胡嘉伟[1] 毛军[1] 郗艳红[1] 刘斌[1] HU Jiawei;MAO Jun;XI Yanhong;LIU Bin(School of Civil Engineering, Beijing Jiaotong University, Beijing 100044, China)

机构地区：[1]北京交通大学土木建筑工程学院,北京100044

出　　处：《华南理工大学学报（自然科学版）》2021年第4期108-116,123,共10页Journal of South China University of Technology(Natural Science Edition)

基　　金：国家重点基础研究项目(2016YFC0802206);国家自然科学基金资助项目(51578061);国家自然科学基金面上项目(52072027);中央高校基础研究经费资助项目(2019JBM087)。

摘　　要：隧道围岩的导热是影响隧道火灾燃烧特性但常常受到忽视的重要因素之一。为研究隧道导热条件对隧道顶棚近壁面区域内火灾烟气蔓延过程的影响,采用数值模拟与全尺寸模型实验相结合的方法,分析了顶棚导热和绝热两种条件下顶棚近壁面区域竖直方向上的温度分布和烟气层特性。结果表明:顶棚强对流烟气沿隧道纵向蔓延时,导热条件下火源下游100 m范围内顶棚下近壁面最大温升出现的高度位置与温度边界层的相似,且最高温升位置与隧道高度之比值的最大值为0.04,高于绝热条件的0.03,出现最高温升的位置距离火源更远。绝热条件下近壁面区域竖直方向温度分布主要受高温烟气卷吸较低层空气的对流换热的影响。在火源功率低于20 MW时,顶棚接触面烟气温度沿隧道纵向呈指数形式衰减,其无量纲温差可用无量纲火源功率与无量纲纵向距离的三分之一次方来表示。导热条件下的烟气与壁面换热造成的损失对顶棚射流温度分布的影响小于绝热条件下卷吸换热的影响,且该热损失量亦沿纵向呈指数形式衰减。Thermal conductivity of surrounding rock is an often neglected and significant factor that affects the fire characteristics of tunnel.To study the influence of thermal conductivity of tunnel on the fire smoke spreading process in near-wall area of tunnel ceiling,the temperature distribution and smoke layer characteristics in the vertical direction beneath heat-conducting ceilings and adiabatic tunnel ceilings were analyzed by means of numerical simulation and full-scale experiment.The results show that when the smoke spreads along the longitudinal direction,the height of maximum temperature rise near wall under the heat-conducting ceiling within 100 m downstream of the fire source is similar to that of the“temperature boundary layer”.The maximum value of the ratio between the maximum temperature rise position and the tunnel height under heat conduction condition is 0.04,which is higher than that under adiabatic condition(0.03),and the position of the maximum temperature is farther away from the fire source.Under adiabatic condition,the temperature distribution in the vertical direction beneath the tunnel ceilings is mainly affected by heat convection caused by the high temperature flue gas entrainment of lower layer air.When the heat release rate is less than 20 MW,the longitudinal temperature attenuation of smoke beneath ceiling contact surface can be expressed as a dimensionless fire power in the form of exponential decay to the power of one third of the dimensionless distance.Additionally,after the temperature boundary layer effect of the ceiling near the wall surface occurs,the smoke temperature of the surface decreases along the longitudinal direction in an exponential form related to the fire power.The influence of the heat transfer loss between the smoke and the wall on the ceiling jet temperature distribution is less than that of the entrainment in the adiabatic condition,and the heat loss also decreases along the longitudinal direction in an exponential form.

关 键 词：隧道火灾 导热 绝热 对流换热 近壁面烟气层 

分 类 号：U458.1[建筑科学—桥梁与隧道工程]