Turbulent superstructures in the turbulent cascade of Reynolds stresses

雷诺应力湍流级联中的湍流上部结构

• 批准号: 429326502
• 负责人: Dr.-Ing. Davide Gatti
• 金额: --
• 依托单位: Institut für Strömungsmechanik (ISTM)
• 依托单位国家: 德国
• 项目类别: Priority Programmes
• 财政年份: 2019
• 资助国家: 德国
• 起止时间: 2018-12-31 至 2023-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/429326502?language=en
• 关键词: Turbulent; superstructures; turbulent; cascade; Reynolds

Vortical structures with different characteristic length scales coexist and interact reciprocally in wall-bounded turbulence. They range from very large-scale structures away from the wall to small-scale eddies in the wall vicinity. The large-scale motions are called turbulent superstructures - TSS in the following – and have length scales much larger than those of the near-wall vortices. TSS play an important role in the dynamics of turbulent flows, where they cause strong velocity fluctuations with a characteristic length scale of many times the largest length scale of the flow, for instance the thickness of a turbulent boundary layer. TSS are responsible for a significant fraction of total turbulent kinetic energy and increased friction drag at the wall, through their contribution to the Reynolds shear stress. Presently, no agreed-upon description of the dynamics of TSS exists, especially concerning their mutual interaction with other scales. While the effect of TSS on the small scale structures at the wall has been documented in literature, there is contrasting evidence regarding an influence in the opposite direction, i.e. an influence of the small scale structures onto the TSS. In particular, it is still unclear whether the small scale structures play a determinant role in the origin of TSS. Understanding the mutual influence of TSS and the other scales of the flow is of great importance not only from a theoretical point of view, but also because it greatly affect our ability to model and control a turbulent flow.In the present proposal we investigate the interaction between TSS and the other smaller scale structures of the flow. We apply a new theoretical framework, the Anisotropic Generalized Kolmogorov Equations, in order to describe how the separate component of the Reynolds stress tensor are produced, dissipated and transported through structures at different length scales and across physical space in the turbulent flow. In this framework, the result of the interaction between scales is a measurable transport of Reynolds stresses across scales and space, that constitutes the so-called turbulent cascade of Reynolds stresses.We develop a series of numerical experiments, in which the physics of turbulent flows in channels is let develop naturally or purposely altered, in order to highlight or quench some aspects of TSS. Through an analysis of how Reynolds stresses are transported through different scales, we can highlight the relationship between TSS and other structures of the turbulent flow.

具有不同特征长度尺度的涡旋结构在壁面湍流中共存并相互作用，它们的范围从远离壁面的非常大尺度的结构到壁面附近的小尺度涡流，这些大尺度运动被称为湍流上层结构——TSS。其长度尺度比近壁涡流大得多，它们在湍流动力学中发挥着重要作用，在湍流中它们会产生强大的速度。特征长度尺度是流动最大长度尺度许多倍的波动，例如湍流边界层的厚度，通过它们的贡献，导致了总湍流动能和壁面摩擦阻力增加的很大一部分。目前，对于 TSS 的动力学还没有达成一致的描述，特别是关于它们与其他尺度的相互作用，虽然文献中已经记录了 TSS 对壁上小尺度结构的影响。对比证据关于相反方向的影响，即小尺度结构对 TSS 的影响，特别是，目前尚不清楚小尺度结构是否在 TSS 的起源中发挥决定性作用。其他尺度的流动不仅从理论角度来看非常重要，而且还因为它极大地影响了我们模拟和控制湍流的能力。在本提案中，我们研究了 TSS 与其他较小尺度结构之间的相互作用我们应用流量。一个新的理论框架，各向异性广义柯尔莫哥洛夫方程，用于描述雷诺应力张量的单独分量如何在不同长度尺度的结构中以及在湍流中穿过物理空间产生、消散和传输。尺度之间相互作用的结果是雷诺应力跨尺度和空间的可测量传输，这构成了所谓的雷诺应力湍流级联。我们开展了一系列数值实验，其中通道中湍流的物理性质可以自然地或有意地改变，以便突出或抑制 TSS 的某些方面。通过分析雷诺应力如何在不同尺度上传输，我们可以突出 TSS 与其他结构之间的关系。湍流。