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首页> 外文期刊>Combustion and Flame >Influence of flow topology and scalar structure on flame-tangential diffusion in turbulent non-premixed combustion
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Influence of flow topology and scalar structure on flame-tangential diffusion in turbulent non-premixed combustion

机译：湍流非预混燃烧中流动拓扑和标量结构对火焰切向扩散的影响

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Flamelet-based combustion models have been extensively used in the modeling of turbulent non-premixed combustion due to their notable advantages in reducing computational cost. The classical one-dimensional flamelet equations are derived based on an assumption: flame-normal transport of thermochemical state variables in mixture fraction gradient direction dominates over flame-tangential transport along iso-surfaces of mixture fraction. The motivation of this work is to quantify the contribution of tangential diffusion (TD) and seek the source of TD, since several recent studies have shown that TD effects may play an important role in the regions with large curvature and finite-rate chemistry. In this work, the most probable cause and effect chain that elucidates the source of TD in a turbulent non-premixed jet flame is proposed for the first time from a flow topology perspective. To this end, local flow topology and its effects on scalar structure are first investigated. It is found that the local flow structures with unstable focus compressing (UFC) topology have the highest probability of large compressive strain and that the negative correlation between curvature and strain strongly depends on local flow topology, scalar structure and reaction. Then, the influence of flow topology and scalar structure on the relevance of TD is assessed with the angle between reactive scalars and mixture fraction. The results show that TD effects mainly exist in the regions with high curvatures and low strain rates or scalar dissipation rates. These findings suggest that the local flow structures with low probability of UFC topology tend to cause significant flame-tangential diffusion in the turbulent non-premixed flame. (C) 2019 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
机译：基于小火焰的燃烧模型由于在降低计算成本方面的显着优势，已广泛用于湍流非预混燃烧的建模。经典的一维小火焰方程是基于以下假设得出的：沿混合分数等值面的火焰切向传输占混合分数梯度方向的热化学状态变量的火焰正态传输占主导地位。这项工作的目的是量化切向扩散（TD）的作用并寻找TD的来源，因为最近的一些研究表明TD效应可能在曲率大且化学性质有限的区域中发挥重要作用。在这项工作中，从流动拓扑的角度首次提出了最可能的因果关系链，该因果链阐明了湍流非预混射流火焰中的TD来源。为此，首先研究了局部流动拓扑及其对标量结构的影响。研究发现，具有不稳定焦点压缩（UFC）拓扑结构的局部流动结构具有较大的压缩应变概率，并且曲率与应变之间的负相关性很大程度上取决于局部流动拓扑结构，标量结构和反应。然后，利用反应性标量与混合比之间的夹角，评估了流动拓扑和标量结构对TD相关性的影响。结果表明，TD效应主要存在于曲率高，应变率或标量耗散率低的区域。这些发现表明，具有低UFC拓扑可能性的局部流动结构倾向于在湍流的非预混火焰中引起明显的火焰切向扩散。 （C）2019燃烧研究所。由Elsevier Inc.出版。保留所有权利。

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