Effect of flow circulation on combustion dynamics of fire whirl
Effect of flow circulation on combustion dynamics of fire whirl
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DOI：
10.1016/j.proci.2012.06.053
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发表时间：
2013
期刊：
影响因子：
--
通讯作者：
K. Zhou;Naian Liu;J. Lozano;Yanlong Shan;B. Yao;K. Satoh
中科院分区：
文献类型：
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作者：
K. Zhou;Naian Liu;J. Lozano;Yanlong Shan;B. Yao;K. Satoh
本文通过实验系统地研究了流动环量对火旋风燃烧动力学的影响。建立了新的火旋风燃烧速率、火焰高度、径向温度和质量流量的关联式。结果表明，流动循环有助于增加燃料与火焰的接触面积和实际燃料表面积，从而增加了燃料表面的热反馈和地面边界层中的径向速度，从而提高了燃烧速率。本文提出了一种新的火旋风火焰高度关联式的概念，即火旋风火焰高度与无环流火焰高度的比值仅表征环流的影响。这一思想得到了充分的验证，从而建立了一个新的火焰高度公式，成功地将燃烧速率和循环量进行了拟合。结果表明，火旋风火焰体中的富燃料核对连续火焰区的径向温度分布有显著影响，火焰体可以用圆柱体和圆锥体的组合来描述。流动循环显著抑制了火羽流半径，从而降低了其随垂直距离的增长率。它还表明，火旋风火焰涉及在其下部的层状区域，共存的湍流区域在上部。流动循环通过改变径向速度分布和增加径向速度来增强在地面层中的空气卷吸。在火焰区的低段，燃烧产物与周围空气的混合物的显著减少主导了流动循环对火焰高度的纯气动效应。最后，它是澄清，火旋风保持较高的中心线过热度比一般池火灾由于较少的空气卷吸的影响。
In this paper, the effect of flow circulation on the combustion dynamics of fire whirl is systematically investigated by experiments. New correlations for the burning rate, flame height, radial temperature and mass flow rate are established for fire whirl. It is clarified that flow circulation helps increase both the fuel-flame contact area and the actual fuel surface area, which in turn increases both the heat feedback to the fuel surface and the radial velocity in the ground boundary layer, leading to increase of burning rate. A novel idea for correlation of fire whirl flame height is proposed by assuming that the ratio of the fire whirl flame height to the flame height without circulation solely characterizes the effect of circulation. This idea is fully verified, thereby a new formulation for flame height is established, which successfully decouples the burning rate and the circulation. It is indicated that the fuel-rich core in the flame body of fire whirl significantly affects the radial temperature distribution in the continuous flame region, and the flame body can be described by the combination of a cylinder and a cone. The flow circulation significantly suppresses fire plume radius and thus decreases its increasing rate with vertical distance. It is also demonstrated that the fire whirl flame involves laminarized regions in its lower section, coexisting with turbulent regions in the upper portion. The flow circulation enhances the air entrainment in the ground layer by altering the radial velocity profile and increasing the radial velocity. In the low section of flaming region, the significant decrease of mixture between the combustion products and surrounding air dominates the pure aerodynamic effect of flow circulation on the flame height. Finally, it is clarified that fire whirls maintain higher centerline excess temperature than general pool fires due to the effect of less air entrainment.