设排烟道隧道的烟气逆流长度与临界风速研究

隧道火灾是运营公路隧道的主要灾害。为有效控制隧道火灾,采用理论分析和数值模拟相结合的方法研究了设排烟道隧道的火灾烟气逆流长度与临界风速。以国内常见的双车道隧道尺寸建立模型,分析了排烟速率和纵向通风速率对烟气逆流长度的影响,提出了临界风速的预测模型。并将其通风效果与常规未设排烟道的纵向通风做了比较。结果表明:未设排烟道时,纵向风速还未达到临界风速时,火灾下游烟气的层化状态就已破坏。设排烟道能及时排出火灾产生的烟气,有利于保持烟气的层化状态,有效改善火灾时的隧道环境,为火灾下游人员的疏散救援提供了有利条件。同时,设置排烟道有利于减小逆流长度和临界风速。随着排烟速率的增大,相应的临界风速呈指数函数递减的特性。

Study of Smoke Backlayering Length and Critical Velocity in Tunnel Fires with Extraction System

The main disaster for operating road tunnels is the tunnel fire.In order to control tunnel fires effectively,theoretical analysis and numerical simulation are conducted to investigate the backlayering length and critical velocity of tunnel fires with extraction system in this paper.A tunnel model is built based on the common size of highway tunnels with double lanes in China.The smoke flow backlayering length is analyzed under different longitudinal ventilation velocity and extraction velocity.Then the prediction model of critical velocity is established.Finally,its ventilation effectiveness is compared with that of common longitudinal ventilation without extraction system.The result shows that for the tunnel without extraction system,smoke stratification in the downstream of fire has been destroyed even though the value of longitudinal ventilation velocity is not up to critical velocity.While extraction system can extract the smoke generating by the fire,which is good for keeping the stratification of smoke layer in the downstream,and providing a good tunnel environment,so it creates a tenable condition for people to evacuate and rescue in the downstream of the fire.And extraction system can reduce backlayering length and critical velocity.As the increase of extraction velocity,corresponding critical velocity decreases with an exponential relation.