隧道受限火灾合理纵向通风风速范围研究

Research on reasonable range of longitudinal ventilation velocity in tunnel confined fire

为探究公路隧道不同受限程度火灾的适宜纵向通风风速,基于FDS模拟分析5种纵向通风速度下不同近壁距离火源顶棚下方烟气最高温度的分布特性、烟羽流倾角及烟气分层状况,提出合理纵向通风风速范围。研究结果表明:在隧道中心线上近火源下游,顶棚下方的最高温度沿纵向均呈指数衰减。不同贴壁距离和纵向通风风速下,均出现烟气分岔流动,随着贴壁距离减小羽流撞击处温升、火羽流偏移角显著增加。当风速小于1.6 m/s时,火源上游出现大量高温烟气回流;而当风速超过2.4 m/s时,分岔流动现象越明显,各偏移角变小,火源下游逐渐后移的烟气层严重失稳。因此,不同受限程度下火灾合理纵向风速为1.6~2.4 m/s。

In order to explore the suitable longitudinal ventilation velocity of highway tunnel fires with different confined degrees,the distribution characteristics of the maximum temperature of smoke under the tunnel ceiling,the inclination angle of smoke plume and the stratification situation of smoke with different near-wall fire source distances under five longitudinal ventilation velocities were simulated and analyzed by FDS,and a reasonable range of longitudinal ventilation velocity was proposed.The results showed that the maximum temperature under the ceiling decreased exponentially near the downstream of fire source on the central line of tunnel.Under different near-wall distances and longitudinal ventilation velocities,the smoke bifurcation flow occurred.With the decrease of near-wall distance,the temperature rise at the plume impact location and the fire plume offset angle increased significantly.When the wind velocity was less than 1.6 m/s,large amount of high-temperature smoke backflow occurred at the upstream of fire source.When the wind velocity exceeded 2.4 m/s,the more obvious the bifurcation flow phenomenon was,the smaller the offset angles were,and the smoke layer gradually moving backward downstream of fire source was seriously unstable.Therefore,the reasonable longitudinal wind velocity of fire under different confined degrees was 1.6 m/s~2.4 m/s.