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On the departure of near-wall turbulence from the quasi-steady state

Published online by Cambridge University Press:  20 May 2019

Lionel Agostini Open the ORCID record for Lionel Agostini [Opens in a new window]  and
Michael Leschziner Open the ORCID record for Michael Leschziner [Opens in a new window]
Lionel Agostini*
Affiliation:
Department of Aeronautics, Imperial College London, London SW7 2AZ, UK
Michael Leschziner
Affiliation:
Department of Aeronautics, Imperial College London, London SW7 2AZ, UK
*
†Email address for correspondence: [email protected]
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Abstract

An examination is undertaken of the validity and limitations of the quasi-steady hypothesis of near-wall turbulence. This hypothesis is based on the supposition that the statistics of the turbulent fluctuations are universal if scaled by the local, instantaneous, wall shear when its variations are determined from footprints of large-scale, energetic, structures that reside in the outer part of the logarithmic layer. The examination is performed with the aid of direct numerical simulation data for a single Reynolds number, which are processed in a manner that brings out the variability of locally scaled statistics when conditioned on the local value of the wall friction. The key question is to what extent this variability is insignificant, thus reflecting universality. It is shown that the validity of the quasi-steady hypothesis is confined, at best, to a thin layer above the viscous sublayer. Beyond this layer, substantial variations in the conditioned shear-induced production rate of large-scale turbulence cause substantial departures from the hypothesis. Even within the wall-proximate layer, moderate departures are provoked by large-scale distortions in the conditioned strain rate that result in variations in small-scale production of turbulence down to the viscous sublayer.

JFM classification

Turbulent Flows: Turbulence modelling Turbulent Flows: Turbulent boundary layers
Type
JFM Rapids
Information
Journal of Fluid Mechanics , Volume 871 , 25 July 2019 , R1
Copyright
© 2019 Cambridge University Press 

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References

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