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Additional spanwise vortices near the free surface in open channel flows

Published online by Cambridge University Press:  12 August 2021

Yanchong Duan Open the ORCID record for Yanchong Duan [Opens in a new window] ,
Qiang Zhong Open the ORCID record for Qiang Zhong [Opens in a new window] ,
Guiquan Wang Open the ORCID record for Guiquan Wang [Opens in a new window] ,
Qigang Chen Open the ORCID record for Qigang Chen [Opens in a new window] ,
Fujun Wang  and
Danxun Li
Yanchong Duan
Affiliation:
State Key Laboratory of Hydroscience and Engineering, Tsinghua University, Beijing 100084, PR China
Qiang Zhong*
Affiliation:
College of Water Resources and Civil Engineering, China Agricultural University, Beijing 100083, PR China Beijing Engineering Research Center of Safety and Energy Saving Technology for Water Supply Network System, China Agricultural University, Beijing 100083, PR China
Guiquan Wang
Affiliation:
Physics of Fluids Group and Twente Max Planck Center, Department of Science and Technology, Mesa+ Institute, and J.M. Burgers Center for Fluid Dynamics, University of Twente, P.O. Box 217, Enschede 7500 AE, The Netherlands
Qigang Chen
Affiliation:
School of Civil Engineering, Beijing Jiaotong University, Beijing 100044, PR China
Fujun Wang
Affiliation:
College of Water Resources and Civil Engineering, China Agricultural University, Beijing 100083, PR China Beijing Engineering Research Center of Safety and Energy Saving Technology for Water Supply Network System, China Agricultural University, Beijing 100083, PR China
Danxun Li
Affiliation:
State Key Laboratory of Hydroscience and Engineering, Tsinghua University, Beijing 100084, PR China
*
†Email address for correspondence: qzhong@cau.edu.cn
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Abstract

This paper reports a new phenomenon in the near-free-surface region of open channel flows (OCFs): namely that higher relative population densities of spanwise vortices are observed than are seen at equivalent positions in turbulent boundary layers. The presence of additional retrograde spanwise vortices in OCFs throughout the region $y/h>0.2$ (where $y$ is the distance to the wall and $h$ is the water depth) prompts us to re-examine the wall-normal extent that the free-surface effect can reach, which is classically expected to be limited within the surface and blockage layers. Finally, possible mechanisms for the phenomenon of additional spanwise vortices in OCFs are provided.

JFM classification

Waves/Free-surface Flows: Channel flow Turbulent Flows: Turbulent boundary layers
Type
JFM Rapids
Information
Journal of Fluid Mechanics , Volume 924 , 10 October 2021 , R3
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Copyright
© The Author(s), 2021. Published by Cambridge University Press

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