隧道火灾集中排烟时机械补风风速研究

 火灾集中排烟模式下,隧道两端射流风机需向隧道内部补充新风,以使排烟区域向火源附近排烟口方向集中,缩小烟气影响范围。从烟气控制效果出发,提出排烟效率、烟气蔓延范围、能见度3个指标作为判定合理机械补风的依据。以某越江隧道工程集中排烟为例,采用火灾动力学模拟软件FDS对-2.8%坡度隧道在不同排烟口开启方案(上游3个/下游3个、上游2个/下游4个、上游1个/下游5个)、不同纵向补风风速(0、1、2、3m/s)下的12 组火灾工况进行模拟计算。结果表明:纵向补风风速对集中排烟效果影响显著,本隧道区段火灾集中排烟时的合理纵向补风风速为2m/s,小于纵向通风时的临界风速值。

Wind Velocity of Longitudinal Air Supply for the Central Smoke Extraction System on Tunnel Fire

Under the mode of central smoke extraction, in the case of a fire occurs inside the tunnel, jet fans at each end are able to operate and provide supply fresh air. The longitudinal fresh air supply is able to prevent smoke from spreading to the both sides of the tunnel, and control the smoke at the opening smoke extraction vents near the fire. Based on smoke control effectiveness, three evaluation indexes are proposed in order to judge the velocity of longitudinal fresh air supply, they are smoke-exhaust efficiency, smoke spread distance, and the visibility distribution at 2m height of the tunnel. Fire Dynamics Simulation (FDS) is employed to run numerical simulations based on a cross-river sloping tunnel. Twelve groups of fires conditions with -2.8% slopes are simulated. Different opening scheme on smoke extraction vents related to the fire location is taken into account. The smoke extraction vents opening schemes includes three upstream vents/three downstream vents, two upstream vents/four downstream vents, one upstream vent/five downstream vents with the mode of one-way central smoke extraction. And different velocities of longitudinal fresh air supply have been considered as well, which are 0 m/s, 1 m/s, 2 m/s, and 3m/s, respectively. The results of the simulation indicate that the reasonable velocity of longitudinal fresh air supply with central smoke extraction mode is 2.0m/s, which is smaller than the critical wind velocity with the same fire condition. Thus, the conclusion is able to help the smoke extraction system to operate effectively and safely.