纵向通风下分岔隧道火灾烟气蔓延特性及控制实验研究

Experimental study on smoke movement characteristics and control in branched tunnel fire under longitudinal ventilation

使用1/10的分岔隧道模型开展缩尺寸实验研究,测量不同火源功率和不同纵向通风风速下隧道内纵向温度分布,定性分析隧道火灾发生时热烟气卷吸空气的机制。结果表明:热烟气卷吸空气的根源在于其自身的斜压性和黏性造成的速度剪切。空气卷吸直接影响了隧道顶棚下方最大温度和烟气的流动状态。当无量纲通风风速小于0.19时,相比于单管隧道,分岔隧道内火羽流能够卷吸到更多的冷空气,因此顶棚下方最大温度比单管隧道的低;当无量纲通风风速大于0.19时,热烟气较多地被吹向下游,热量分配形式近似与单管隧道,因此顶棚下方最大温度接近单管隧道。随着通风风速的增加,空气卷吸强度增加,烟气层分层现象不明显。分岔隧道中一部分纵向通风风流能够进入支路隧道,因此其临界风速较单管隧道高。提出了适用于本文考虑的分岔隧道的临界风速计算模型,发现无量纲临界风速与无量纲热释放速率仍然具有与单管隧道类似的1/3幂次关系。

Reduced-scale experiments were conducted using 1/10 branched tunnel model.The temperature field of hot smoke in the tunnel was measured under different heat release rates and different longitudinal ventilation velocities.The mechanism of air entrainment of hot smoke in the tunnel fire was qualitatively analyzed.The results show that the ultimate motivation of air entrainment is the baroclinicity and velocity shear due to viscosity of hot smoke.The air entrainment directly affects the maximum temperature beneath the ceiling.When the dimensionless ventilation velocity is less than 0.19,fire plume in branched tunnel fire could entrain more ambient air,which reduces the maximum temperature.When ventilation velocity is higher than 0.19,most heat are blown downstream.The allocation of heat is similar to that of single-tube tunnel.In such circumstances,the maximum temperature is close to that of single-tube tunnel.With increase of ventilation velocity,the air entrainment strengthens,and smoke stratification is destroyed gradually.Since a part of the hot smoke in the branched tunnel can enter the branch tunnel,the air entrainment is less,so the critical ventilation velocity is higher than that of the single tunnel.According to the experimental data,a critical ventilation velocity model was proposed for branched tunnel concerned in this paper.It was found that the dimensionless critical velocity and dimensionless heat release rate still have power relations similar to that of single tunnel.