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Morphology and structure of hydrogen-air turbulent premixed flames

机译：氢空气湍流预混火焰的形态和结构

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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 Damkohler 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 Damkohler 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. (C) 2018 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
机译：分析了波纹小火焰和薄反应区中湍流预混平面火焰的直接数值模拟，以研究湍流对火焰结构和形态的影响。基于平面不变性和丝状性的基于拓扑不变性的工具，称为shapefinder，用于评估火焰形态。几项统计数据表明，丝状度代表湍流对火焰形态的集总效应，与达姆霍勒数紧密相关，而与卡洛维兹数则不相关。为了研究哪种湍流波动尺度是火焰形态演化的原因，研究了Kolmogorov长度尺度和Taylor尺度的条件平均值。条件平均值显示泰勒微尺度与丝状度之间有很强的相关性，而柯尔莫哥洛夫长度尺度没有观察到类似的强相关性。这些结果表明，在相对较大的Damkohler数条件下，与火焰形态相关的湍流-火焰相互作用的长度尺度大于泰勒尺度。为DNS和具有不同过滤器大小的已过滤反应进程变量字段计算分形维数。在分辨的和泰勒-微米级滤波场之间计算的分形维数几乎相同。而且，表明当使用泰勒微米级的过滤器尺寸时，火焰表面积的93-97％被回收。但是，当将积分长度标度用于过滤器尺寸时，该分数会迅速降低。对于火焰起皱因子也观察到类似的趋势。 （C）2018年燃烧研究所。由Elsevier Inc.出版。保留所有权利。

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