Numerical study of under-ventilated fire in medium-scale enclosure
Numerical study of under-ventilated fire in medium-scale enclosure
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DOI：
10.1016/j.buildenv.2008.09.011
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发表时间：
2009-06
影响因子：
7.4
通讯作者：
Hui Wang
中科院分区：
文献类型：
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作者：
Hui Wang
在封闭空间内，当所有的空气流入都被多余的燃料燃烧消耗时，内部火焰进入衰减阶段，这种过程被称为火焰排气。采用大涡模拟方法研究了从初始火焰生长到火焰排出再到外部燃烧的复杂多阶段过程。湍流燃烧过程采用涡破裂概念，采用两个连续的半全局步骤进行CO预测。数值模型求解三维，时间相关的Navier-Stokes方程，再加上子模型的烟尘形成和热辐射传输。在中等规模的设施中，火焰排出所需的临界燃料供应速率和从燃料点燃到外部火焰出现的时间段先前由Chamchine AV、Graham TL、Makhviladze GM等人通过实验获得。[中小型封闭空间内通风不足燃烧的实验研究。载于：第四届火灾和爆炸危险国际研讨会会议记录; 2003年。第97-107页]，数值模型预测的总趋势与实验观测结果吻合得很好。该模型能够充分描述发生在室内火灾中的基本同时现象（火焰高度、烟尘生成、CO生成、对流和辐射）。分析了火焰排气和排气情景之前火灾发展的不同瞬态阶段。在封闭空间内的火焰排出之后，接着是外部燃烧，并且超过天花板的火焰高度Hf近似于开口高度的数量级。即使在临界条件下发生火焰排气，从较热气体和外部火源传递的热量也对外壳内的人员构成重大威胁，并可能引起暴露在外壳开口附近的燃料包的点燃。
In an enclosure, as all the air inflow is consumed in burning with the excess fuel, the internal fire enters the decay phase, and such process is said flame exhaust. The complicated multistage process from an initial fire growth up to a flame exhaust followed by an external burning is investigated by means of a Large-Eddy-Simulation (LES). Turbulent combustion process is modelled by an Eddy Break-Up concept by using two sequential, semi-global steps for CO prediction. The numerical model solves three dimensional, time-dependent Navier–Stokes equations, coupled with submodels for soot formation and thermal radiation transfer. The critical fuel supply rate needed for flame to exhaust and the time period from the fuel ignition to the appearance of an external flaming in medium-scale facilities are previously obtained experimentally by Chamchine AV, Graham TL, Makhviladze GM, et al. [Experimental studies of under-ventilated combustion in small and medium-scale enclosures. In: Proceedings of the fourth international seminar on fire and explosion hazards; 2003. p. 97–107.], and the general trends predicted by the numerical model follow closely their experimental observation. This model is capable of adequately describing the essential simultaneous phenomena (flame height, soot generation, CO production, convection and radiation) occurring in a room fire. The distinct transient stages of fire development prior to flame exhaust and scenarios of the exhaust are analysed. An external burning is followed after the flame exhaust inside enclosure, and the flame height, Hf, past the ceiling is approximately in an order of the opening height. Even though the flame exhaust takes place under the critical conditions, the heat transferred from the hotter gases and the external fire source poses significant threat to people inside enclosure, and potentially induces an ignition of fuel package exposed near the opening of an enclosure.