观察到的液池火特性对涡流大小的依赖性
Observed dependence of characteristics of liquid-pool fires on swirl magnitude
摘要：
在实验室中，将12个垂直取向的薄矩形叶片（62 cm高和15.2 cm宽）放置在距离庚烷和乙醇池火中心27 cm处的直径为3.2 cm和5.1 cm的连续进料的地板冲洗盘中。叶片都以与径向方向相同的固定角度定向，对于9个不同的角度，范围从0度到85度，从而赋予每个池火夹带的空气9个不同水平的循环。不同的漩涡水平，观察到产生显着不同的池火结构。适度的涡流抑制了整体的抽吸不稳定性，取而代之的是一个整体的螺旋不稳定性，产生一个高大的火旋风，其高度增加，增加流通。除了最大的庚烷池，更高的涡流水平产生的旋涡破裂，导致出现的气泡状回流区与环涡环绕轴。测量的燃烧速率随着涡流水平的增加而增加，这是由于相关的增加的流入速度减小了边界层的厚度，在该边界层内，燃烧发生在液体表面的正上方，最终在边界层中形成分离的边缘火焰，该边缘火焰随着循环的增加而移近轴线。更高的循环通过减少火焰覆盖的液体的表面积来降低燃烧速率，从而降低火旋风的高度。甚至更高的循环导致边缘火焰分离，导致在最近的文献中确定的蓝色漩涡的形成，通常在本实验中的液体表面蜿蜒。本文件记录了该事件序列。
英文摘要：
One dozen vertically oriented thin rectangular vanes, 62 cm tall and 15.2 cm wide, were placed 27 cm from the center of heptane and ethanol pool fires in continuously fed, floor-flush pans 3.2 cm and 5.1 cm in diameter in the laboratory. The vanes were all oriented at the same fixed angles from the radial direction, for 9 different angles, ranging from 0 to 85 degrees, thereby imparting 9 different levels of circulation to the air entrained by each pool fire. The different swirl levels were observed to engender dramatically different pool-fire structures. Moderate swirl suppresses the global puffing instability, replacing it by a global helical instability that generates a tall fire whirl, the height of which increases with increasing circulation. Except for the largest heptane pool, higher swirl levels produced vortex breakdown, resulting in the emergence of a bubble-like recirculation region with a ring vortex encircling the axis. Measured burning rates increase with increasing swirl levels as a consequence of the associated increasing inflow velocities reducing the thickness of the boundary layer within which combustion occurs right above the liquid surface, eventually forming detached edge flames in the boundary layer that move closer to the axis as the circulation is increased. Still higher circulation reduces the burning rate by decreasing the surface area of the liquid covered by the flame, thereby reducing the height of the fire whirl. Even higher circulation causes edge-flame detachment, resulting in formation of the blue whirl identified in recent literature, often meandering over the surface of the liquid in the present experiments. This sequence of events is documented herein.
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