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) localizes 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.

中文翻译：

---

将湍流界面的时间演化与相干结构联系起来

湍流/非湍流界面 (TNTI) 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，通过 TNTI 区域的时间演化方程，在有和没有稳定分层的湍流中研究了负责 TNTI 区域增长和破坏的机制。我们表明这两个术语都有广泛的分布，并且可能在局部对生产或破坏做出贡献。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，我们对数据应用空间过滤。在这样做，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，并且这种逐尺度平衡与观察到的附近相干涡旋的尺度不变性一致。通过条件分析，我们证明 TNTI 区域的产生（破坏）位于界面附近的涡旋结构的前（背风）边缘。最后，我们表明，虽然基本机制保持不变，但增加分层会降低 TNTI 表面积产生和破坏的速度。我们提供的证据表明，这种减少在很大程度上与界面的多尺度几何形状的变化有关，在 TNTI 的所有活动长度尺度上，它往往在壁法向方向上变平。