Chakraborty Nilanjan, Wang Lipo, Klein Markus
School of Mechanical and Systems Engineering, Newcastle University Claremont Road, Newcastle-Upon-Tyne NE1 7RU, UK.
UM-SJTU Joint Institute, Shanghai JiaoTong University, Shanghai 200240, China.
Phys Rev E Stat Nonlin Soft Matter Phys. 2014 Mar;89(3):033015. doi: 10.1103/PhysRevE.89.033015. Epub 2014 Mar 26.
The interaction of flame and surrounding fluid motion is of central importance in the fundamental understanding of turbulent combustion. It is demonstrated here that this interaction can be represented using streamline segment analysis, which was previously applied in nonreactive turbulence. The present work focuses on the effects of the global Lewis number (Le) on streamline segment statistics in premixed flames in the thin-reaction-zones regime. A direct numerical simulation database of freely propagating thin-reaction-zones regime flames with Le ranging from 0.34 to 1.2 is used to demonstrate that Le has significant influences on the characteristic features of the streamline segment, such as the curve length, the difference in the velocity magnitude at two extremal points, and their correlations with the local flame curvature. The strengthenings of the dilatation rate, flame normal acceleration, and flame-generated turbulence with decreasing Le are principally responsible for these observed effects. An expression for the probability density function (pdf) of the streamline segment length, originally developed for nonreacting turbulent flows, captures the qualitative behavior for turbulent premixed flames in the thin-reaction-zones regime for a wide range of Le values. The joint pdfs between the streamline length and the difference in the velocity magnitude at two extremal points for both unweighted and density-weighted velocity vectors are analyzed and compared. Detailed explanations are provided for the observed differences in the topological behaviors of the streamline segment in response to the global Le.
火焰与周围流体运动的相互作用对于深入理解湍流燃烧至关重要。本文表明，这种相互作用可以用流线段分析来表示，该方法先前应用于非反应性湍流。目前的工作重点是全局刘易斯数（Le）对薄反应区预混火焰中流线段统计量的影响。利用一个直接数值模拟数据库，该数据库包含了自由传播的薄反应区火焰，Le的范围从0.34到1.2，结果表明Le对流线段的特征有显著影响，如曲线长度、两个极值点处速度大小的差异以及它们与局部火焰曲率的相关性。随着Le的减小，膨胀率、火焰法向加速度和火焰产生的湍流的增强是造成这些观测效应的主要原因。最初为非反应湍流流动开发的流线段长度概率密度函数（pdf）表达式，在很宽的Le值范围内捕捉到了薄反应区湍流预混火焰的定性行为。分析并比较了未加权和密度加权速度矢量的流线长度与两个极值点处速度大小差异之间的联合概率密度函数。针对观察到的流线段拓扑行为因全局Le而异的情况提供了详细解释。
