Abstract Longitudinal ventilation is widely employed for smoke control in tunnels due to its relatively low installation cost and compactness. However, smoke control using a longitudinal ventilation system becomes complex when applied in a multi-branch sloping tunnel. In sloping tunnels, the stack effect and forced longitudinal ventilation may combine to produce multiple smoke flow patterns, even under identical or similar boundary conditions. Furthermore, such flow multiplicity behavior is considerably more complicated in a multi-branch sloping tunnel than in a single sloping tunnel. In this paper, an optimal longitudinal ventilation strategy was proposed to prevent smoke flow multiplicity induced by the combined buoyancy- and pressure-driven effects of a downhill sloping, longitudinally ventilated multi-branch tunnel fire. The ventilation network of the multi-branch tunnel was divided into three basic regions: the branches upstream of the intersection node, an on/off-ramp, and the other branches downstream of the intersection node. Based on this division and a hydraulic analysis, the multi-branch tunnel was characterized as a system consisting of several three-branch structures. The critical fan-induced pressure rise required to prevent smoke flow multiplicity was then derived by a potential analysis method according to the fire location in the tunnel. The optimal strategy was achieved by integrating the fan-induced pressure rises in each tunnel branch. The results reveal that the total pressure at the branch intersection node can be varied to regulate the integrated fan-induced pressure rise in each branch. The efficiency of this strategy in preventing flow multiplicity for all typical fire source locations in a three-branch structure was then demonstrated via numerical simulations. The proposed approach has implications for improving tunnel emergency ventilation design and fire protection.

中文翻译：

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纵向通风倾斜多支路交通隧道火灾中多种浮力和压力驱动组合流模式的预防

摘要 纵向通风由于其安装成本较低且结构紧凑，被广泛应用于隧道排烟。然而，当应用于多分支倾斜隧道时，使用纵向通风系统的烟雾控制变得复杂。在倾斜隧道中，即使在相同或相似的边界条件下，烟囱效应和强制纵向通风也可能结合产生多种烟气流动模式。此外，这种流动多重性行为在多分支倾斜隧道中比在单个倾斜隧道中复杂得多。在本文中，提出了一种最佳纵向通风策略，以防止由下坡、纵向通风的多分支隧道火灾的浮力和压力驱动的组合效应引起的烟气流动多样性。多支路隧道的通风网络分为三个基本区域：交叉口节点上游的分支、出入口匝道和交叉口节点下游的其他分支。基于这种划分和水力分析，多分支隧道被描述为一个由几个三分支结构组成的系统。然后根据隧道中的火灾位置，通过潜在分析方法推导出防止烟流多重性所需的临界风扇引起的压力升高。最佳策略是通过整合每个隧道分支中风扇引起的压力上升来实现的。结果表明，可以改变分支交叉节点处的总压力以调节每个分支中集成的风扇引起的压力升高。然后通过数值模拟证明了该策略在防止三分支结构中所有典型火源位置的流动多重性方面的效率。所提出的方法对改善隧道应急通风设计和防火有影响。