Numerical Study of the Effects of Confinement on Concurrent-Flow Flame Spread in Microgravity
Numerical Study of the Effects of Confinement on Concurrent-Flow Flame Spread in Microgravity
复制标题
微重力条件下约束对顺流火焰传播影响的数值研究
DOI：
10.1115/1.4047645
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发表时间：
2020-08
期刊：
影响因子：
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通讯作者：
Yanjun Li;Ya-Ting T. Liao;P. Ferkul
中科院分区：
文献类型：
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作者：
Yanjun Li;Ya-Ting T. Liao;P. Ferkul
这项工作的目的是研究蔓延火焰与周围墙壁之间的空气动力学和热相互作用及其对火灾行为的影响。采用三维非稳态计算流体力学(CFD)燃烧模型，模拟了窄流道中顺流火焰在薄固体样品上的传播。流道高度是主要参数。数值结果预测了流动管道的熄灭高度，低于该高度火焰不会扩散。对于足够大于淬火高度的管道高度，火焰在样品完全消耗之前达到稳定的扩散状态。火焰传播速率和稳态热解长度随流道高度的减小先增大后减小。详细的气体和固体分布表明，流动约束对火焰传播过程有多方面的影响。一方面，它加速了燃烧产生的热膨胀过程中的流动，强化了火焰。另一方面，增加流动限制减少了对火焰的氧气供应，增加了对壁面的传导热损失，这两者都削弱了火焰。这些相互竞争的影响导致了前述火焰传播率随管道高度变化的非单调趋势。在淬火通道高度附近，瞬变模型揭示了火焰在长度、火焰温度和火焰结构上的振荡。这种现象被怀疑是由于热扩散不稳定性造成的。
The objective of this work is to investigate the aerodynamics and thermal interactions between a spreading flame and the surrounding walls as well as their effects on fire behaviors. A three-dimensional transient computational fluid dynamics (CFD) combustion model is used to simulate concurrent-flow flame spread over a thin solid sample in a narrow flow duct. The height of the flow duct is the main parameter. The numerical results predict a quenching height for the flow duct below which the flame fails to spread. For duct heights sufficiently larger than the quenching height, the flame reaches a steady spreading state before the sample is fully consumed. The flame spread rate and the pyrolysis length at steady-state first increase and then decrease when the flow duct height decreases. The detailed gas and solid profiles show that flow confinement has multiple effects on the flame spread process. On one hand, it accelerates flow during thermal expansion from combustion, intensifying the flame. On the other hand, increasing flow confinement reduces the oxygen supply to the flame and increases conductive heat loss to the walls, both of which weaken the flame. These competing effects result in the aforementioned nonmonotonic trend of flame spread rate as duct height varies. Near the quenching duct height, the transient model reveals that the flame exhibits oscillation in length, flame temperature, and flame structure. This phenomenon is suspected to be due to thermodiffusive instability.