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Influence of the slope in the ventilation semi-transversal system of an urban tunnel

机译：坡度对城市隧道通风半横向系统的影响

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The covering of a section of the Inner Belt roadway ("Ronda del Mig") in Barcelona gives rise to an urban tunnel of great length (1535 m). The tunnel is divided into two independent parallel galleries and its orientation is North-South, with a 2% upward slope towards the North. Although normal ventilation is achieved with jet fans, between the two galleries there is an interior passage for smoke extraction, in case of fire, through exhaust openings on both sides of this passage. Therefore, the tunnel has a semi-transversal ventilation system for fire incidents. The behavior of the smoke generated during those possible fire incidents in the traffic galleries was simulated with a commercial code, FLUENT~®, which allows a three-dimensional multispecies Navier-Stokes unsteady simulation. The mesh of each tunnel was made with about 250,000 triangular base prismatic cells. The simulated fire had a thermal power of 30 MW and the time step was set to one second, while the simulation covered 15 min. Special emphasis was put on the influence of the tunnel slope on the smoke's behavior in each gallery. Simulation results showed that the fans' capacity established in the project specifications was not enough to extract the smoke of a fire with the simulated power. A significant percentage of the smoke was aspirated through the exhaust openings but the rest continued rising to the tunnel portal due to the slope. This created a great risk mainly in the descending gallery with opposite traffic direction. For a more efficient extraction it was determined that the exhaust sections should be opened upward of the fire's location. The standard opening, at both sides of the fire, reduced the capacity to extract smoke due to clean air aspiration from the lower portal.
机译：巴塞罗那的内带车道（“ Ronda del Mig”）的一部分被覆盖，形成了一条长度很大（1535 m）的城市隧道。隧道分为两个独立的平行廊道，其方向为南北向，向北向上倾斜2％。尽管射流风扇可实现正常通风，但在两个通道之间有内部通道，在着火时，通过该通道两侧的排气孔可排烟。因此，该隧道具有半横向通风系统以应对火灾。使用商业代码FLUENT？模拟了交通走廊在那些可能发生的火灾中产生的烟雾的行为，该代码允许进行三维多物种Navier-Stokes非稳态模拟。每个隧道的网格由大约250,000个三角形的基础棱柱形单元构成。模拟火灾的火力为30 MW，时间步长设置为一秒，而模拟时间为15分钟。特别强调了隧道坡度对每个画廊内烟雾行为的影响。仿真结果表明，在项目规范中确定的风扇容量不足以用模拟功率提取火气。很大一部分烟气是通过排气口吸入的，但由于倾斜，其余烟气继续上升到隧道入口。这主要在下行方向相反的下行通道中产生了很大的风险。为了更有效地进行抽风，已确定排气段应在火源位置上方打开。壁炉两侧的标准开口减少了由于从下部门口吸入干净空气而导致的排烟能力。

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