强降雨作用下隧道火灾烟气蔓延特性及控制试验

Experimental Study on Control of Smoke Movement in Tunnel Fires Under Heavy Rainfall

为探究强降雨对隧道火灾烟气蔓延特性及烟气控制的影响,基于Froude准则搭建了1∶15的缩尺模型隧道试验台,设置了4个不同的降雨强度、4个火源功率以及6个纵向通风速度,对强降雨作用下的隧道火灾烟气蔓延进行试验研究。结果表明:降雨发生时,隧道洞口在降雨作用下产生压差,最终在隧道内诱导形成纵向气流;诱导气流速度随降雨强度的增大而增大。降雨强度较大时,火源上游的烟气在诱导气流的限制下无法从火源上游洞口处溢出;对强降雨作用下的隧道火灾烟气进行纵向通风控制时,纵向通风气流的驱动力一部分用于消除热烟驱动力带来的烟气回流趋势,另一部分用于抵消降雨诱导气流在隧道内的影响。试验结果发现回流长度、临界风速均随降雨强度的增大而增大。火源功率为3.03、6.06、9.09、12.12 kW时,临界风速在强降雨作用下分别提高25.6%、17%、14%以及9%,说明强降雨对隧道火灾烟气纵向通风控制的作用随火源功率的增大而减小。基于前人模型和试验结果建立了强降雨作用下隧道火灾临界风速的量纲一的预测模型,明晰了强降雨影响隧道火灾烟气蔓延及控制的机制。

This study investigates the effect of heavy rainfall on the smoke-movement characteristics and smoke control of tunnel fires using a reduced-scale(1∶15)experimental platform based on the Froude criterion.A series of tunnel fire tests was conducted based on four different rainfall intensities,four heat-release rates,and six longitudinal ventilation velocities.The results show that the flow field at the tunnel entrance is affected by raindrop behaviors,such as diffusion and drag,when heavy rainfall occurs.Induced airflow is directed downstream of the tunnel.When the rainfall intensity increases,the induced airflow velocity increases and smoke is restricted upstream of the tunnel.The first part of the longitudinal ventilation velocity was used to eliminate back-layering caused by the hot-smoke driving force,and the other part was used to offset the effect of induced airflow in the tunnel.The back-layering length increases with the rainfall intensity.The accuracy of the critical wind speed was verified based on a previous model.Under fire-source power levels of 3.03,6.06,9.09,and 12.12 kW,the critical ventilation velocity increased by 25.6%,17%,14%,and 9%under the effect of heavy rainfall,respectively.The higher the heat-release rate,the less affected is the critical ventilation velocity by heavy rainfall.Based on the temperature-distribution law of a tunnel ceiling subjected to heavy rainfall,the mechanism by which heavy rainfall affects smoke movement was clarified,and the effect of heavy rainfall on the key parameters for tunnel-disaster prevention and ventilation design was investigated.