湍流预混火焰的分形特性

Fractal Nature of Turbulent Premixed Flame

采用高速纹影摄影法获得了定容燃烧弹内预混湍流火焰的图像,分别用数盒子法和像素点覆盖法计算出了火焰图像的分形维数。湍流火焰的分形分析结果表明,定容燃烧弹内的预混湍流火焰结构具有分形特征,且属于非充分发展的湍流火焰。湍流火焰的分形维数反应了湍流脉动对火焰片的褶皱程度,湍流强度增大加剧湍流火焰前锋的褶皱,分形维数也随之增加。在相同湍流强度下,小尺度湍流对火焰前锋的褶皱作用更大。

As the high speed schlieren photographs of turbulent premixed combustion in a constant volume combustion bomb are recorded, the counting boxes method and the pixel-covering method are used to calculate the fractal dimensions of theses motion images respectively. The results show that there is a fractal characteristic in turbulent premixed flame structure, and the turbulent premixed flames aren't fully developed. The fractal dimension of flame structure indicates the extent of turbulent wrinkling, and an appropriate increase of turbulence intensity results in the increase of wrinkling extent, i.e. that the fractal dimension increases. The wrinkling will enhance for the smaller turbulent scale under the same turbulence intensity.