How do turbulent superstructures interact with skin friction drag?

湍流上部结构如何与表面摩擦阻力相互作用？

• 批准号: 316200959
• 负责人: Professorin Dr.-Ing. Bettina Frohnapfel
• 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: 2016
• 资助国家: 德国
• 起止时间: 2015-12-31 至 2022-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/316200959?language=en
• 关键词: How; do; turbulent; superstructures; interact

Although turbulent superstructures (TSS) are known to leave a substantial footprint on near-wall turbulence, relatively little is known about their quantitative impact on the momentum transport from fluid to the wall, which corresponds to the skin friction drag. Results obtained within the first funding period indicate that the removal of TSS is not a promising approach for drag reduction as the flow undergoes complex restructuring and new structures at smaller scales emerge. In addition, changes of large scale structures in drag reduced flows were shown to be predictable based on the effective channel height and Reynolds number of drag reduced controlled flows only. This suggests that TSS exist rather autonomously from the near-wall turbulence cycle which is in agreement with recent literature findings. As the numerical experiments in the first phase are limited to a Reynolds number range in which TSS and the related scale interaction is only weakly present (which is a common challenge in this field of research), we plan to work with a model system of TSS in the second phase. This system consists of a turbulent channel flow in which streamwise ridges are placed along the channel walls. Secondary motions in the form of large-scale streamwise vortices are formed above those ridges which are known to carry the characteristic properties of naturally occurring TSS at higher Reynolds numbers. In a concerted numerical and experimental study we will investigate the interaction of those TSS with skin friction drag in combination with the related scale interaction and indications for flow control through the introduction (instead of the removal) of TSS. The collaborations within the first phase of the Priority Programme (SPP) in respect to the detection of TSS revealed that especially the small scale dispersion in turbulent flows is challenging for the detection coherent structures. Therefore, a number of different filtering approaches will be considered by different groups within the second funding period. In the present project we will consider a filter based on a reduced order model of the secondary motion. This filtered data set along with the full data set of the numerical simulation will be made available to other groups within the SPP that mainly work on the effective detection of TSS. The present project thus contributes to the following goals of the SPP: - quantification of the impact of TSS on global transport and turbulence statistics- understanding the mechanics of TSS and the role of boundary conditions - developing approaches for control and efficient modelling of TSS in reduced models

虽然湍流超结构（TSS）是众所周知的，留下了大量的足迹近壁湍流，相对较少的是知道他们的定量影响的动量传输从流体到壁，这对应于表面摩擦阻力。在第一个供资期内获得的结果表明，去除TSS并不是一种有希望的减阻方法，因为流动经历了复杂的重组，并且出现了较小尺度的新结构。此外，减阻流中大尺度结构的变化仅根据有效通道高度和减阻控制流的雷诺数即可预测。这表明，TSS存在，而自主的近壁湍流循环，这是在最近的文献研究结果。由于在第一阶段的数值实验是有限的雷诺数范围内，TSS和相关的规模相互作用是只有微弱的存在（这是一个共同的挑战，在这一领域的研究），我们计划在第二阶段与TSS的模型系统。该系统由湍流槽道流组成，其中流向脊沿沿着槽壁布置。大尺度流向涡形式的二次运动形成在这些脊的上方，这些脊在较高雷诺数下具有自然发生的TSS的特征特性。在一个协调一致的数值和实验研究中，我们将调查这些TSS与表面摩擦阻力的相互作用，结合相关的规模相互作用和流动控制的迹象，通过引入（而不是删除）的TSS。优先计划第一阶段在TSS探测方面的合作表明，特别是湍流中的小尺度色散对探测相干结构具有挑战性。因此，在第二个供资期内，不同的小组将考虑一些不同的筛选办法。在本项目中，我们将考虑基于二次运动降阶模型的滤波器。该过滤后的数据集沿着数值模拟的完整数据集将提供给SPP内主要致力于有效检测TSS的其他小组。因此，本项目有助于实现SPP的以下目标：-量化TSS对全球输送和湍流统计的影响-了解TSS的力学和边界条件的作用-在简化模型中开发TSS控制和有效建模的方法