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The structure and dynamics of backflow in turbulent channels

Published online by Cambridge University Press:  07 October 2019

J. I. Cardesa Open the ORCID record for J. I. Cardesa [Opens in a new window] ,
J. P. Monty Open the ORCID record for J. P. Monty [Opens in a new window] ,
J. Soria Open the ORCID record for J. Soria [Opens in a new window]  and
M. S. Chong
J. I. Cardesa
Affiliation:
School of Aeronautics, Universidad Politécnica de Madrid, 28040 Madrid, Spain
J. P. Monty
Affiliation:
Department of Mechanical Engineering, University of Melbourne, Victoria 3010, Australia
J. Soria
Affiliation:
Laboratory for Turbulence Research in Aerospace and Combustion, Department of Mechanical and Aerospace Engineering, Monash University (Clayton Campus), Melbourne 3800, Australia
M. S. Chong
Affiliation:
Department of Mechanical Engineering, University of Melbourne, Victoria 3010, Australia
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Abstract

A statistical description of flow regions with negative streamwise velocity is provided based on simulations of turbulent plane channels in the Reynolds number range $547\leqslant Re_{\unicode[STIX]{x1D70F}}\leqslant 2003$. It is found that regions of backflow are attached and their density per surface area – in wall units – is an increasing function of $Re_{\unicode[STIX]{x1D70F}}$. Their size distribution along the three coordinates reveals that, even though in the mean they appear to be circular in the wall-parallel plane, they tend to become more elongated in the spanwise direction after reaching a certain height. Time-tracking of backflow regions in a $Re_{\unicode[STIX]{x1D70F}}=934$ simulation showed they convect downstream at the mean velocity corresponding to $y^{+}\approx 12$, they seldom interact with other backflow events, their statistical signature extends in the streamwise direction for at least $300$ wall units, and they result from a complex interaction between regions of high and low spanwise vorticity far beyond the viscous sublayer. This could explain why some statistical aspects of these near-wall events do not scale in viscous units; they are dependent on the $Re_{\unicode[STIX]{x1D70F}}$-dependent dynamics further away from the wall.

JFM classification

Turbulent Flows: Turbulence simulation Boundary Layers: Boundary layer structure Turbulent Flows: Turbulent boundary layers
Type
JFM Rapids
Information
Journal of Fluid Mechanics , Volume 880 , 10 December 2019 , R3
Copyright
© 2019 Cambridge University Press 

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Footnotes

†

Present address: Institut de Mécanique des Fluides de Toulouse (IMFT), Université de Toulouse, 31400 Toulouse, France. Email address for correspondence: [email protected]

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