Experimental and theoretical study on near-floor flame spread along a thin solid
Experimental and theoretical study on near-floor flame spread along a thin solid
复制标题
近地板火焰沿薄固体传播的实验和理论研究
DOI：
10.1016/j.proci.2018.06.001
复制
发表时间：
2018
影响因子：
3.4
通讯作者：
G. Kushida and S. Yazaki
中科院分区：
文献类型：
--
作者：
M. Goto;K. Kuwana;G. Kushida and S. Yazaki
本文介绍了近地面火焰沿薄固体扩散的实验观察和理论。实验是通过点燃一张薄薄的圆形纸的中心来进行的，这张纸被举在离底层一定高度的地方。结果表明：h较小时，火焰前缘呈波纹状，常破裂成分离结构；h= 2 mm时，火焰前缘出现高度扰动燃烧区；在h= 1 mm时火焰不可能蔓延。另一方面，当h大于约5 mm时，扩散呈近轴对称分布，扩散速度随h的增大而增大。由于前缘结构与阴燃燃烧相似，因此基于阴燃扩散理论进行了分析，其中氧化剂流速和热损失程度是两个重要参数。边界层考虑和PIV测量表明，在所研究的条件下，氧化剂的流动速度没有显著变化，从而表明热损失对底层的重要性。然后导出了描述前法向速度的方程，并对其进行了数值求解。由于切向速度不会改变曲线的形状，因此对其进行了调整，使格点间距渐近均匀。理论预测的不同h值下的锋形演化与实验观测结果相当吻合，至少在定性上验证了理论。
This paper presents experimental observations and a theory of near-floor flame spread along a thin solid. Experiments were conducted by igniting at the center of a thin circular paper sheet that was held at a given height h from the bottom floor. It was observed that the flame front was corrugated and often broke into separated structures when h was small, and highly disturbed burned areas were obtained for h= 2 mm; flame spread was not possible at h= 1 mm. When h was larger than about 5 mm, on the other hand, nearly axisymmetric spread was observed, and the spread velocity was found to increase with h. Since the front structure showed a similarity with smoldering combustion, an analysis was conducted based on a theory of smoldering spread, in which oxidizer flow velocity and the degree of heat loss are two important parameters. Boundary-layer consideration and PIV measurement showed that the oxidizer flow velocity did not significantly vary under the conditions studied, thereby suggesting the importance of heat loss to the bottom floor. An equation that describes the front normal velocity was then derived, which was numerically solved. Since the tangential velocity does not alter the shape of a curve, it was adjusted such that the grid-point spacing would be asymptotically uniform. Theoretically predicted front-shape evolution for different values of h agreed reasonably well with the experimental observations, validating the theory at least qualitatively.