Morphology and structure of hydrogen-air turbulent premixed flames
Morphology and structure of hydrogen-air turbulent premixed flames
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氢-空气湍流预混火焰的形态与结构
DOI：
10.1016/j.combustflame.2018.02.019
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发表时间：
2018
影响因子：
4.4
通讯作者：
Tanahashi Mamoru
中科院分区：
文献类型：
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作者：
Minamoto Yuki;Yenerdag Basmil;Tanahashi Mamoru
通过对波纹小片和薄反应区的湍流预混平面火焰的直接数值模拟，研究了湍流对火焰结构和形态的影响。利用一种基于拓扑不变量的工具来评估火焰形态，该工具由平面度和细丝度组成。一些统计表明，表示湍流对火焰形态的集中效应的细丝度与Damköhler数密切相关，但与Karlovitz数无关。为了研究湍流波动的哪个尺度对火焰形态演化负责，研究了Kolmogorov长度尺度和Taylor微尺度的条件平均。条件平均表明泰勒微尺度与细丝度之间存在较强的相关性，而在柯尔莫哥洛夫长度尺度上没有观察到类似的强相关性。这些结果表明，在相对较大的Damköhler数条件下，与火焰形态相关的湍流-火焰相互作用发生在大于泰勒微尺度的长度尺度上。计算了不同滤料尺寸的DNS和过滤后的反应过程变量场的分形维数。计算得到的分形维数在分辨场和泰勒微尺度滤波场之间几乎相同。结果表明，采用泰勒微尺度的过滤尺寸时，火焰表面积可回收93 ~ 97%。然而，当使用积分长度尺度作为过滤器尺寸时，这个分数迅速下降。火焰起皱因子也有类似的变化趋势。
Direct numerical simulations of turbulent premixed planar flames in the corrugated flamelets and thin reaction zones regimes are analysed to investigate the effect of turbulence on the flame structure and morphology. A tool based on topological invariants called shapefinders, consisting of the planarity and filamentarity, is applied to assess the flame morphology. Several statistics show that the filamentarity, which represents lumped effects of the turbulence on the flame morphology, is closely correlated with the Damköhler number, but not with the Karlovitz number. To investigate which scale of turbulent fluctuations is responsible for the flame morphology evolution, the conditional averages of the Kolmogorov length scale and the Taylor microscale are studied. The conditional averages show strong correlation between the Taylor microscale and the filamentarity, while similar strong correlation is not observed for the Kolmogorov length scale. These results suggest that the turbulence–flame interaction relevant to the flame morphology occurs at the length scale greater than the Taylor microscale for relatively large Damköhler number conditions. The fractal dimension is computed for the DNS and filtered reaction progress variable fields with different filter sizes. The computed fractal dimensions between the resolved and the Taylor-microscale filtered fields are almost identical. Also, it was shown that 93–97% of flame surface area is recovered when the filter size of the Taylor microscale is used. However, this fraction rapidly decreases when the integral length scale is used for the filter size. A similar trend was observed for the flame wrinkling factor.