Ahmed Umair, Chakraborty Nilanjan, Klein Markus
School of Engineering, Newcastle University, Newcastle Upon-Tyne, NE1 7RU, UK.
Bundeswehr University Munich, Department of Aerospace Engineering, Werner Heisenberg Weg 39, D-85577, Neubiberg, Germany.
Sci Rep. 2019 Mar 25;9(1):5092. doi: 10.1038/s41598-019-41599-y.
The interaction of large and small scale structures is fundamental to the energy cascade in turbulent flows. The correct representation of this interaction becomes important in the context of large eddy simulation (LES), where the response of small-scale structures to the resolved quantities, or large-scale structures, must be parametrised. This challenging task becomes more demanding when LES of premixed flames are considered, as heat release affects the interaction of turbulence and chemistry occurring at the unresolved scales. In this work, the influence of sub-grid scale (SGS) stresses on the kinetic energy budget of the resolved velocity field in turbulent premixed flames is investigated. In this spirit, the alignment between the SGS stresses and the resolved strain rate has been analysed by interrogating a direct numerical simulation (DNS) database of statistically planar premixed flames subjected to forced isotropic turbulence. It has been found that the alignment between the eigenvectors of the SGS stresses and the resolved strain rate changes across the flame brush and this change is dependent on the level of turbulence experienced by the flame. The influence of different turbulence intensities and different filter widths along with the implications of this misalignment on the SGS modelling are discussed in detail in the paper.
大尺度结构与小尺度结构的相互作用是湍流中能量级串的基础。在大涡模拟（LES）的背景下，这种相互作用的正确表示变得很重要，在大涡模拟中，小尺度结构对解析量或大尺度结构的响应必须进行参数化。当考虑预混火焰的大涡模拟时，这项具有挑战性的任务变得更加艰巨，因为热释放会影响未解析尺度上发生的湍流与化学反应的相互作用。在这项工作中，研究了亚网格尺度（SGS）应力对湍流预混火焰中解析速度场动能收支的影响。本着这种精神，通过研究一个统计平面预混火焰在强迫各向同性湍流作用下的直接数值模拟（DNS）数据库，分析了SGS应力与解析应变率之间的对齐情况。研究发现，SGS应力的特征向量与解析应变率之间的对齐在火焰刷上会发生变化，并且这种变化取决于火焰所经历的湍流水平。本文详细讨论了不同湍流强度和不同滤波宽度的影响以及这种不对齐对SGS建模的影响。
