Pool Flame Instability Characteristics under Transverse Acoustic Wave Disturbance
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摘要:
为理解声波灭火机制及声波扰动下的火焰动力学，进行了横向低频声波扰动乙醇池火燃烧实验. 采用的低频声波频率范围为28 ~ 54 Hz，火焰位置处当地声压范围为0.10 ~ 1.25 Pa，通过改变声波导流管长度和声波导流管与火焰距离研究了声学基础参数、火焰现象学特征、火焰高度与宽度及其周期性脉动特性，并建立了耦合声波参数的火焰宽度与高度模型. 研究结果表明：相比自由火焰，较低声压扰动使火焰形态与时序变化更加稳定，较大声压扰动会使火焰失稳；随当地声学雷诺数增加，火焰相对高度被声波压制而减小，火焰宽度由被挤压转变为被拓展状态；较低声压会调制火焰导致其周期性变得更稳定，相位变得规则，较高声压会扰乱火焰周期性，使得火焰脉动紊乱，相位变得混沌.
Abstract:Ethanol pool flame experiments disturbed with transverse low-frequency acoustic wave were carried out to understand the mechanism of acoustic fire suppression and flame dynamics under acoustic disturbance. The acoustic frequency range was 28–54 Hz, and the local acoustic pressure range at the flame was 0.10–1.25 Pa. The basic acoustic parameters, phenomenological characteristics of flame, flame height and width, and flame periodic pulsation were explored with the changing acoustic duct length and distance between acoustic duct and flame. The relation model of flame width and flame height coupled with acoustic parameters was established. The results show that, compared with free flame, the lower acoustic pressure disturbance makes the flame shape and time series more stable, and the larger acoustic pressure disturbance makes the flame more unstable. With increasing Reynolds number locally, the relative flame height is suppressed by acoustic wave and declined, and the flame width changes from being compressed to being lengthened. In addition, lower acoustic pressure will modulate flame to stable periodicity and regular phase. Higher acoustic pressure will disturb flame periodicity, resulting in flame pulsation disorder and phase chaos.
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Key words:
- acoustic wave /
- pool fire /
- instability /
- fire suppression /
- ethanol
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图 1 声波扰动火焰燃烧实验示意
Figure 1. Schematic of flame combustion experiment with acoustic disturbance
图 2 不同实验条件下的声压变化
Figure 2. Acoustic pressure change under different experimental conditions
图 3 自由火焰与N2-W5实验条件下的火焰概率云图
Figure 3. Probability contours of free flame and flame under experimental conditions of N2-W5
图 4 火焰图像的时序分析（N2-W5，34 Hz）
Figure 4. Time series analysis of flame image (N2-W5, 34 Hz)
图 5 火焰细节结构特征分析示意
Figure 5. Schematic of structure characteristics analysis of flame detail
图 6 声波扰动下相对火焰高度变化
Figure 6. Relative flame height variation under acoustic disturbance
图 7 火焰相对高度随声学雷诺数变化
Figure 7. Variation of relative flame height with acoustic Reynolds number
图 8 声波扰动下火焰相对宽度变化
Figure 8. Variation of relative flame width under acoustic disturbance
图 10 无量纲火焰高度与宽度关系
Figure 10. Relationship between dimensionless flame height and width
图 11 自由及0.36 Pa声波扰动下火焰参数Iʹ(t) 随时间的变化（N2-W5，34 Hz）
Figure 11. Variation of flame parameter Iʹ(t) with time under free state and 0.36 Pa acoustic disturbance (N2-W5, 34 Hz)
图 12 自由及0.36 Pa声波扰动下火焰参数Iʹ(t) 周期和相位图（N2-W5, 34 Hz）
Figure 12. Period and phase diagram of flame parameter Iʹ(t) under free state and 0.36 Pa acoustic disturbance (N2-W5, 34 Hz)
图 13 0.73 Pa声波扰动下火焰参数Iʹ(t) 变化（N2-W5，34 Hz）
Figure 13. Variation of flame parameter Iʹ(t) under 0.73 Pa acoustic disturbance (N2-W5, 34 Hz)
图 14 0.73 Pa声波扰动下火焰参数Iʹ(t) 的周期和相位（N2-W5, 34 Hz）
Figure 14. Period and phase diagram of flame parameter Iʹ(t) under 0.73 Pa acoustic disturbance (N2-W5, 34 Hz)
表 1 实验采用的参数
Table 1. Experimental parameters
cm 实验简称 Ln Lw 实验简称 Ln Lw N2-W5 2 5 N10-W0 10 0 N2-W10 2 10 N10-W10 10 10 N5-W0 5 0 N15-W0 15 0 N5-W10 5 10 N15-W10 15 10 
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