The bottom boundary-layer structure of fire whirls
The bottom boundary-layer structure of fire whirls
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DOI：
10.1016/j.proci.2018.05.009
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发表时间：
2019
影响因子：
3.4
通讯作者：
Shangpeng Li;Q. Yao;C. Law
中科院分区：
文献类型：
--
作者：
Shangpeng Li;Q. Yao;C. Law
在燃料池上方的火旋风的底部边界层耦合到外部旋转流、汽化过程和随后的气体中的扩散燃烧。因此，它在火旋风的动力学中起着至关重要的作用，特别是产生的燃烧速率和火焰高度。本文对旋转屏产生的典型层流火旋风的底部边界层结构进行了数值和理论研究。相关的局部相似性解决方案的动量和耦合函数的推导，导致火焰的配置以及表面气化率的确定。结果表明，随着旋流强度的增加，底部边界层变薄，火焰底部更靠近池面。结果，所施加的循环通过增强对流热传递和燃料的蒸发，特别是在燃料池的外部区域中，增加了燃烧速率，从而增加了火旋风的火焰高度。在很宽的Ekman数Ek和Grashof数Gr范围内，理论结果与模拟结果在定性和定量上都吻合得很好。
The bottom boundary layer of a fire whirl over a fuel pool is coupled to the outer rotating flow, the vaporization process, and the subsequent diffusional burning in the gas. As such, it plays an essential role in the dynamics of the fire whirl, particularly the resulting burning rate and flame height. In this paper, the bottom boundary-layer structure of a typical laminar fire whirl, generated by a rotating screen, is investigated both numerically and theoretically. The associated local similarity solutions of the momentum and coupling functions are derived, leading to the determination of the flame configuration as well as the surface gasification rate. It is demonstrated that the bottom boundary layer becomes thinner and the flame base is closer to the pool surface as the swirl intensity increases. As a result, the applied circulation increases the burning rate and thereby the flame height of the fire whirl by enhancing the convective heat transfer and the evaporation of the fuel, especially in the outer region of the fuel pool. The theoretical results agree well with the simulation results over a wide range of the Ekman numberEkand the Grashof numberGr, both qualitatively and quantitatively.