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A Simple Model for the Movement of Fire Smoke in a Confined Tunnel

机译：密闭隧道内火烟运动的简单模型

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摘要

Fires in tunnels are unfortunately frequent occurrences often with tragic outcomes. A recent example is the fire on the funicular train at the ski resort in Kaprun (Austria), which caused nearly 160 deaths. Design engineers and risk analysts require knowledge of the fluid dynamics of the fire and smoke movement to answer questions such as how much oxygen can access and feed the fire, and what concentration of smoke will the people be exposed to. As an example in the Austrian accident the geometry was a long tunnel with fire doors closed at one end, and with a fire initiated near the closed (lower) end. The hot smoke from the fire is a source of buoyancy; the smoke reaches the ceiling of the tunnel, and then develops along the ceiling as a wall-bounded plume. The motion of the smoke is driven by a buoyancy force, but at the same time, mechanisms of turbulent heat and mass transfer act as a brake to this motion. In this paper we present how a generic model describing a semi-enclosed buoyancy-driven flow can be interpreted and used in the modelling of fire smoke movement in a confined tunnel. A consideration of the net pollutant volume flux through the tunnel leads to predictions for the variation of concentrations along the tunnel. The smoke concentrations near the fire smoke source scale linearly with the length of the tunnel, with higher concentrations at the lower section of the tunnel, as could be expected. Similarly the concentration of oxygen making its way through to the fire source decreases linearly with the length of the tunnel. A lower bound estimate of the smoke residence time can be obtained based on smoke concentration predictions from the model.
机译：不幸的是，隧道失火是经常发生的，往往造成悲剧性后果。最近的一个例子是奥地利卡普伦（Kaprun）滑雪胜地的缆车上的大火，造成近160人死亡。设计工程师和风险分析人员需要了解火灾和烟气运动的流体动力学，才能回答诸如氧气可以进入并供给火源以及人们将要接触的烟雾浓度之类的问题。以奥地利事故为例，该几何形状是一条长隧道，一端防火门一端关闭，而靠近封闭（下端）的地方引发了火灾。大火产生的热烟是浮力的来源。烟雾到达隧道的天花板，然后沿着天花板扩散成一堵墙。烟雾的运动是由浮力驱动的，但与此同时，湍流热和质量传递的机制也阻止了这种运动。在本文中，我们介绍了如何解释描述半封闭浮力驱动流的通用模型，并将其用于密闭隧道中烟气运动的建模。通过隧道的净污染物体积通量的考虑导致对沿隧道浓度变化的预测。可以预料，靠近火源的烟雾浓度与隧道的长度成线性比例，在隧道的下部较高。同样，穿过火源的氧气浓度随隧道的长度线性降低。烟雾停留时间的下限估计值可以基于模型中的烟雾浓度预测值获得。

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