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Effects of circulation and buoyancy on the transition from a fire whirl to a blue whirl
Physical Review Fluids ( IF 2.5 ) Pub Date : 
Sriram Bharath Hariharan, Yu Hu, Michael J. Gollner, Elaine S. Oran

The relative influence of circulation and buoyancy on fire whirls (FW), blue whirls (BW), and the transition between these regimes of a whirling flame is investigated using a combination of experimental data and scaling analyses. FWs are whirling, turbulent, cylindrical yellow (sooting) flame structures that form naturally in fires and are here created in laboratory experiments. In contrast, a BW is a laminar, blue flame (non-sooting) with an inverted conical shape. Prior measurements of the circulation and heat-release rate are now combined with additional measurements of the flame geometry, particularly the width and height, to provide characteristic length scales for these flames. Using these, a nondimensional circulation (Γf*) and heat-release rate (Q̇f*) were defined and shown to correspond to azimuthal (buoyancy driven) and axial momenta, respectively. The ratio *=Γf*/Q̇f*, a quantity analogous to the swirl number used to characterize swirling jets, was evaluated for FWs and BWs. For FWs, *1, so that the flame is circulation dominated. This is argued to be consistent with vortex breakdown being an important part of the transition of FWs to BWs. This work presents a basis for predicting when a BW will form and remain a stable regime. [Keywords] \emph{blue whirl; fire whirl; scaling; vortex breakdown …

中文翻译:

循环和浮力对从火旋风向蓝色旋风过渡的影响

结合实验数据和定标分析,研究了循环和浮力对旋涡(FW),蓝涡(BW)以及这些状态之间的过渡的相对影响。FW是在燃烧中自然形成的旋转,湍流,圆柱形黄色(发汗)火焰结构,在此处是通过实验室实验创建的。相反,BW是层状蓝色火焰(不发火),圆锥形倒置。现在将循环和放热率的先前测量值与火焰几何形状(尤其是宽度和高度)的其他测量值结合起来,以提供这些火焰的特征长度标度。使用这些,无量纲循环(ΓF*)和放热率(̇F*定义并显示为分别对应于方位角(浮力驱动)和轴向动量。比例*=ΓF*/̇F*评估了FW和BW的量,该量类似于用于表征旋流喷嘴的旋流数。对于固件,*1个,使火焰以循环为主。认为这与涡流破裂是一致的,这是FW向BW过渡的重要部分。这项工作为预测BW何时形成并保持稳定状态提供了基础。[关键字] \ emph {blue whirl; 火旋风 缩放 涡旋破坏……
更新日期:2020-09-10
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