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

尽管众所周知，湍流的上层建筑（TSS）在近壁湍流方面留下了很大的占地面积，但对于它们对从流体到墙的动量运输的定量影响相对较少，这对应于皮肤摩擦的阻力。在第一个资金期间获得的结果表明，随着流量经历复杂的重组和较小尺度的新结构，TSS的去除不是阻力减少的一种有希望的方法。此外，基于有效的通道高度和雷诺数仅减少受控流量，大规模减少流量中的大规模结构的变化被证明是可以预测的。这表明TSS与近期文献发现一致的近壁湍流周期中存在自主存在。由于第一阶段中的数值实验仅限于雷诺数范围，在该范围内，TSS和相关规模相互作用仅存在薄弱（这在这一研究领域是一个普遍的挑战），因此我们计划在第二阶段与TSS模型系统合作。该系统由湍流的流量组成，其中流向沿通道墙的流向脊。大规模流涡流形式形式的次要运动在山脊上方形成，这些山脊在较高的雷诺数下具有天然发生的TSS的特征性特性。在一项协同的数值和实验研究中，我们将研究这些TSS与皮肤摩擦阻力的相互作用与相关规模的相互作用以及通过TSS的引入（而不是去除）的流动控制指示。优先计划（SPP）在TSS检测方面的合作表明，尤其是湍流流中的小规模分散体对于检测相干结构而言是挑战。因此，在第二个融资期内，不同的组将考虑许多不同的过滤方法。在本项目中，我们将根据次级运动的减少顺序模型来考虑一个过滤器。该过滤数据集以及数值模拟的完整数据集将提供给SPP中的其他组，主要用于有效检测TSS。因此，本项目有助于SPP的以下目标： - TSS对全球运输和湍流统计的影响量化 - 了解TSS的力学和边界条件的作用 - 开发用于控制模型中TSS的控制方法和有效建模的方法