Coherent superstructures in turbulent pipe and Taylor-Couette flows

自然界和工程中的流体运动通常具有大尺度相干运动的特征，即所谓的超结构，其强烈地由边界条件、几何形状和驱动源形成。湍流上层结构携带相当大的一部分动能，它们有助于阻力，并且它们通常支配整个流体系统的热、质量和动量传输特性。因此，为了超越国家的最先进的建模和控制策略的湍流，上层建筑必须正确占。在这个项目中，我们将调查的动力学，能量学和输运特性的上层建筑在两个典型的设置：圆柱管流和泰勒-库埃特流两个旋转同心圆柱体之间，特别是在窄间隙限制。首先，我们将确定上层建筑是否通过小得多的尺度的相干排列或直接从平均切变中获得能量。我们将实现这一目标，通过计算直接数值模拟数据的尺度间的能量通量（空间）过滤方法。第二，为了帮助各小组在优先方案内开发表征和检测方法，我们将提供和维护高分辨率的数据集，这些数据集将使用我们的过滤工具自适应地降低空间和时间复杂性。利用这些方法，我们将研究拉格朗日相干结构与能流之间的关系。我们的工作将建立在第一个资助阶段建立的合作网络的基础上，并将允许弥合目前的高雷诺数差距。

Fluid motions in nature and engineering typically feature large-scale coherent motions, so-called superstructures, which are strongly shaped by boundary conditions, geometry and source of driving. Turbulent superstructures carry a substantial part of the kinetic energy, they contribute to drag and they often dominate heat, mass and momentum transport properties of the entire fluid system. Hence, in order to go beyond state-of-the-art modelling and control strategies of turbulent flows, superstructures must be correctly accounted for. In this project, we will investigate the dynamics, energetics and transport properties of superstructures in two canonical setups: cylindrical pipe flow and Taylor--Couette flow between two rotating concentric cylinders, especially in the narrow-gap limit. First, we will determine whether superstructures harvest energy through coherent alignment of much smaller scales, or directly from the mean shear. We will achieve this by computing the inter-scale energy flux from direct numerical simulation data with a (spatially) filtering approach. Second, in order to aid the groups developing characterisation and detection methods within the Priority Programme we will offer and maintain highly-resolved data sets, which will be adaptively reduced in spatial and temporal complexity using our filtering tools. With these methods, we will investigate the relationship between Lagrange coherent structures and energy fluxes. Our work will build upon the network of collaborations established in the first funding phase and will allow bridging the current gap towards high Reynolds numbers.