Connecting the time evolution of the turbulence interface to coherent structures
Connecting the time evolution of the turbulence interface to coherent structures
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DOI：
10.1017/jfm.2020.414
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发表时间：
2020-01
影响因子：
3.7
通讯作者：
M. M. Neamtu-Halic-M.;D. Krug;J. Mollicone;M. van Reeuwijk;G. Haller;M. Holzner
中科院分区：
文献类型：
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作者：
M. M. Neamtu-Halic-M.;D. Krug;J. Mollicone;M. van Reeuwijk;G. Haller;M. Holzner
湍流/非湍流界面（TNTIs）的表面积通过拉伸和曲率/传播效应不断产生和破坏。在这里，负责TNTI面积的增长和破坏的机制进行了研究，在湍流和不稳定分层通过时间演化方程的TNTI面积。我们表明，这两个条款有广泛的分布，并可能在当地有助于生产或销毁。然而，平均而言，面积增长是由拉伸驱动的，这与曲率/传播项的破坏大致平衡。为了研究不同长度尺度对这些过程的贡献，我们对数据进行了空间滤波。在这样做时，我们发现，拉伸和曲率/传播项的平均值在TNTI皱纹的空间尺度上平衡，这种尺度平衡与附近相干涡旋的尺度不变性相一致。通过条件分析，我们表明，TNTI区生产（破坏）是本地化的前（李）边缘的旋涡结构在接口附近。最后，我们表明，虽然基本的机制保持不变，增加分层降低TNTI表面积的生产率，以及销毁。我们提供的证据表明，这种减少在很大程度上是连接到多尺度几何的界面，这往往是在所有的有效长度尺度的TNTI在壁法线方向变平的变化。
The surface area of turbulent/non-turbulent interfaces (TNTIs) is continuously produced and destroyed via stretching and curvature/propagation effects. Here, the mechanisms responsible for TNTI area growth and destruction are investigated in a turbulent flow with and without stable stratification through the time evolution equation of the TNTI area. We show that both terms have broad distributions and may locally contribute to either production or destruction. On average, however, the area growth is driven by stretching, which is approximately balanced by destruction by the curvature/propagation term. To investigate the contribution of different length scales to these processes, we apply spatial filtering to the data. In doing so, we find that the averages of the stretching and the curvature/propagation terms balance out across spatial scales of TNTI wrinkles and this scale-by-scale balance is consistent with an observed scale invariance of the nearby coherent vortices. Through a conditional analysis, we demonstrate that the TNTI area production (destruction) is localized at the front (lee) edge of the vortical structures in the interface proximity. Finally, we show that while basic mechanisms remain the same, increasing stratification reduces the rates at which TNTI surface area is produced as well as destroyed. We provide evidence that this reduction is largely connected to a change in the multiscale geometry of the interface, which tends to flatten in the wall-normal direction at all active length scales of the TNTI.