Self-Sustaining Process of Townsend’s Attached Eddies in High-Reynolds-Number Wall Turbulence

高雷诺数壁面湍流中汤森附着涡流的自持过程

• 批准号: EP/N019342/1
• 负责人: Yongyun Hwang
• 金额: $ 11.9万
• 依托单位: Imperial College London
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2016
• 资助国家: 英国
• 起止时间: 2016 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=EP%2FN019342%2F1
• 关键词: Self; Sustaining; Process; Townsend; Attached

Over the past decade, significant progress on understanding the coherent structures in wall turbulence has been made, especially in twofold. One is discovery of the non-trivial exact solutions of the Navier-Stokes equation, known as exact coherent structures, which has allowed for tackling low-Reynolds-number turbulence with dynamical system approaches. The other, initiated by discovery of new coherent structures emerging much further from wall at high Reynolds numbers, is the emerging evidence supporting Townsend's attached eddy hypothesis, which views that all the coherent structures, the size of which varies from the inner to outer length scale, are self-similar and form a hierarchial organisation.Recently, the single eddy entity in the hierarchial organisation, called attached eddy, has been computed by our group, providing compelling evidence on the existence of the attached eddy. It has been found that the computed attached eddies exhibit the physical features highly reminiscent of those of the exact coherent structures. The goal of the proposed research is therefore to establish a theoretical link between the Townsend's attached eddies and the exact coherent structures in high-Reynolds-number wall turbulence. To achieve this, two work packages are proposed, one of which is to examine the detailed physical processes of a single attached eddy (especially streak instability) and the other is to directly compute the exact coherent structures associated with the given attached eddy.The proposed research will be an important step towards a consistent theoretical description of statistical and dynamical features of the coherent structures in a wide range of the Reynolds numbers, covering from transitional (especially bypass transition) to fully-developed turbulent regime. It will also have a great potential to contribute to understanding and controlling wall turbulence at high Reynolds numbers, crucial for development of next generation aeronautical and mechanical engineering devices.

在过去的十年中，在理解壁湍流的相干结构方面取得了重大进展，特别是在双重湍流中。一是发现了纳维-斯托克斯方程的非平凡精确解，称为精确相干结构，它允许用动力系统方法解决低雷诺数湍流。另一个是由发现在高雷诺数下距壁更远的新相干结构引发的，是支持汤森附加涡流假说的新证据，该假说认为所有大小从内部到外部长度尺度不同的相干结构都是自相似的，并形成一个层次结构。最近，层次结构中的单个涡流实体，称为附加涡流，已被研究出来。 由我们小组计算得出，为附加涡流的存在提供了令人信服的证据。人们发现，计算出的附着涡流表现出的物理特征与精确的相干结构的物理特征高度相似。因此，本研究的目标是在汤森附加涡流与高雷诺数壁面湍流中精确的相干结构之间建立理论联系。为了实现这一目标，提出了两个工作包，其中一个是检查单个附加涡流（尤其是条纹不稳定性）的详细物理过程，另一个是直接计算与给定附加涡流相关的精确相干结构。所提出的研究将是朝着对大范围雷诺数中相干结构的统计和动力学特征进行一致理论描述迈出的重要一步，涵盖从过渡（尤其是旁路） 过渡）到完全发展的湍流政权。它还具有巨大的潜力，有助于理解和控制高雷诺数下的壁湍流，这对于下一代航空和机械工程设备的开发至关重要。

项目成果

Self-sustaining processes at all scales in wall-bounded turbulent shear flows.

壁面湍流剪切流中所有尺度的自持过程。

• DOI: 10.1098/rsta.2016.0088
• 发表时间: 2017
• 期刊: Philosophical transactions. Series A, Mathematical, physical, and engineering sciences
• 作者: Cossu C

Self-sustaining process of minimal attached eddies in turbulent channel flow

• DOI: 10.1017/jfm.2016.226
• 发表时间: 2016-04
• 期刊: Journal of Fluid Mechanics
• 影响因子: 3.7
• 作者: Y. Hwang;Yacine Bengana

Streak instability in near-wall turbulence revisited

重新审视近壁湍流中的条纹不稳定性

• DOI: 10.1080/14685248.2017.1294757
• 发表时间: 2017
• 期刊: Journal of Turbulence
• 影响因子: 1.9
• 作者: Cassinelli A

The mesolayer of attached eddies in wall-bounded turbulent flows

壁界湍流中附着涡流的中层

• 发表时间: 2017
• 期刊: 10th International Symposium on Turbulence and Shear Flow Phenomena, TSFP 2017
• 作者: Hwang Y.

Streak instability in turbulent channel flow: the seeding mechanism of large-scale motions

• DOI: 10.1017/jfm.2017.697
• 发表时间: 2017-09
• 期刊: Journal of Fluid Mechanics
• 影响因子: 3.7
• 作者: Matteo de Giovanetti;H. Sung;Y. Hwang