Upward flame spread and self‐induced buoyant blow‐off over two‐sided thin fabric at different inclination angles
Upward flame spread and self‐induced buoyant blow‐off over two‐sided thin fabric at different inclination angles
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DOI：
10.1002/fam.3021
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发表时间：
2021-08
影响因子：
1.9
通讯作者：
Yunji Gao;Xiaolong Yang;Yueyang Luo;F. Guo;Yu-chun Zhang;Liang Gong
中科院分区：
文献类型：
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作者：
Yunji Gao;Xiaolong Yang;Yueyang Luo;F. Guo;Yu-chun Zhang;Liang Gong
在从水平（0°）到垂直（90°）的不同倾斜角度下，在双面长薄亚麻织物片材上进行了一系列向上火焰蔓延实验。当倾角增加到临界角时，4厘米和6厘米宽的样品下侧的火焰可以自发吹灭。下侧吹气后，上侧残留的火焰稳定地蔓延到样品的末端。为了阐明控制机制，研究并比较了不同倾斜角度下的火焰蔓延速率和火焰几何特征。在自感浮力的帮助下，最大火焰蔓延速率和火焰长度随着倾斜角度单调增加。然而，一侧熄灭后，剩余一侧的稳定火焰蔓延速率和火焰长度显着下降。下侧火焰被临界火焰长度引起的大浮力流速吹走，临界火焰长度由小 Damköhler 数控制。在不同的倾斜度下分析火焰厚度和火焰倾斜角，以帮助了解从火焰到未燃烧燃料表面的热传递。在不同的倾角范围内提出了自感浮力的两种相反的效果：较低倾角的热辅助状态和较高倾角的动力学灭火状态。它们分别由火焰的传热和火焰底部周围的局部流体动力学决定。
A series of upward flame spread experiments over two‐sided long thin flax fabric sheets were conducted at different inclination angles from horizontal (0°) to vertical (90°). With the inclination increased to a critical angle, the flame on the lower side of the 4 and 6 cm wide samples can be blown off spontaneously. After the lower‐side blow‐off, the remained flame on the upper side spread steadily to the end of the sample. To clarify the controlling mechanism, the flame spread rates and flame geometry characteristics were investigated and compared in different inclination angles. The maximum flame spread rate and flame length monotonically increased with the inclination angle under the assistance of self‐induced buoyancy. However, the steady flame spread rate and flame length on the remained side dropped significantly after one‐side extinction. The lower side flame was blown off by the large buoyant flow velocity induced from the critical flame length, which is controlled by the small Damköhler number. Flame thickness and flame tilt angle were analyzed at varied inclinations to help understand the heat transfer from the flame to the unburnt fuel surface. Two opposite effects of self‐induced buoyancy were proposed at different ranges of inclination: the thermal assistance regime at the lower inclination angle and the kinetical extinguishing regime at a higher inclination angle. They are dominated by the heat transfer from the flame and local fluid dynamic around the flame base, respectively.