纵向风作用下城市隧道火灾烟气分岔流动特性研究

发布时间：2019-06-12 11:06

【摘要】：当城市隧道内发生火灾后，其狭长的内部结构为救援工作的开展带来一定的阻碍，火灾产生的烟气和热量大大影响了救援的速度，容易造成大量的人员伤亡和财产损失，因此对城市隧道内火灾烟气流动的研究非常重要，可以有效指导隧道的灭火和人员疏散，对隧道内防排烟设计也具有很大的指导意义。 本文采用FDS大涡模拟方法和1/10小尺寸实验对纵向风下隧道火灾烟气分岔流动现象进行研究，研究表明随着纵向风速的增大，隧道火灾烟气流动汇聚区逐渐远离羽流撞击区，出现分岔流动，隧道顶棚形成一个几乎无烟气存在的中心低温区，研究还揭示了烟气分岔流动的产生是由烟气浮力和纵向风惯性力所决定的。另外，在通过数值模拟研究火源位置对烟气流动情况影响时发现，随着火源逐渐靠近侧壁，烟气流动由对称分岔流动转变为不对称分岔流动，最后向两侧流动的烟气逐渐汇聚呈“S”型流动。 本文研究发现，烟气分岔流动临界风速即羽流撞击区上游烟气逆流完全消失时的最小风速。利用FDS模拟计算改变火源热释放速率和隧道高度时的分岔流动临界风速，得出烟气分岔流动临界风速与无量纲火源热释放速率的1/3次方成正比，是烟气逆流临界风速的1.48倍，建立烟气分岔流动临界风速预测模型，并通过一系列小尺寸实验验证该模型的可行性。 最后本文通过数值模拟对纵向风下不同位置处竖井排烟进行研究和比较。研究表明，烟囱效应和边界层分离现象影响竖井的排烟效果，纵向风速较小时（1m/s），烟囱效应引起的吸穿现象导致竖井排烟能力较差，随着风速的增大，吸穿现象消失，竖井排烟能力增强，，当风速过大时（2.5m/s），明显的边界层分离现象将减弱竖井的排烟能力。通过对竖井口CO体积流率的比较发现各竖井在纵向风速为1-1.5m/s时排烟效果最佳，且对于与火源有相同径向距离的竖井，侧壁竖井与中心竖井排烟能力相差不大，基于实际隧道工程的需要，在竖井位置设计时可优先选择侧壁竖井，另外，竖井的排烟能力随着竖井逐渐远离火源而逐渐减弱，因此，在设计排烟竖井间距时，需把该因素考虑在内。
[Abstract]:When there is a fire in the urban tunnel, its narrow internal structure brings some obstacles to the development of the rescue work. The smoke and heat generated by the fire greatly affect the speed of rescue, and it is easy to cause a large number of casualties and property losses. Therefore, the study of fire smoke flow in the urban tunnel is very important, which can effectively guide the fire fighting and evacuation of the tunnel. It also has great guiding significance for the design of smoke prevention and exhaust in tunnel. In this paper, FDS large vortex simulation method and 1 脳 10 small size experiment are used to study the phenomenon of smoke bifurcation flow in tunnel fire under longitudinal wind. The results show that with the increase of longitudinal wind speed, the convergence area of tunnel fire smoke flow is gradually away from the plume impact area, and the bifurcation flow occurs, and a central low temperature zone with almost no smoke exists in the tunnel roof. It is also revealed that the generation of flue gas bifurcation flow is determined by smoke buoyancy and longitudinal wind inertia. In addition, when the influence of fire source position on flue gas flow is studied by numerical simulation, it is found that with the fire source approaching the side wall, the smoke flow changes from symmetrical bifurcation flow to asymmetric bifurcation flow, and finally the smoke flowing to both sides gradually converges into "S" type flow. In this paper, it is found that the critical wind speed of flue gas bifurcation flow is the minimum wind speed when the upstream flue gas countercurrent in the plume impact zone disappears completely. The critical wind speed of bifurcation flow is calculated by FDS simulation when the heat release rate of fire source and tunnel height are changed. It is concluded that the critical wind speed of flue gas bifurcation flow is proportional to the 1 鈮

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