Skin-friction generation by attached eddies in turbulent channel flow
File(s)
Accepted version
Author(s)
de Giovanetti, M
Hwang, Y
Choi, H
Type
Journal Article
Abstract
Despite a growing body of recent evidence on the hierarchical organization of the selfsimilar
energy-containing motions in the form of Townsend’s attached eddies in wallbounded
turbulent flows, their role in turbulent skin-friction generation is currently
known very little. In this paper, the contribution of each of these self-similar energycontaining
motions to turbulent skin friction is explored up to Reτ ≃ 4000. Three
different approaches are employed to quantify the skin-friction generation by the motions,
the spanwise length scale of which is smaller than a given cut-off wavelength: 1) FIK
identity in combination with the spanwise wavenumber spectra of the Reynolds shear
stress; 2) confinement of the spanwise computational domain; 3) artificial damping of
the motions to be examined. The near-wall motions are found to continuously lose their
role in skin-friction generation on increasing the Reynolds number, consistent with the
previous finding at low Reynolds numbers. The largest structures given in the form of
very-large-scale and large-scale motions are also found to be of limited importance: due
to a non-trivial scale-interaction process, their complete removal yields only 5 ∼ 8% of
skin-friction reduction at all the Reynolds numbers considered, although they are found
to be responsible for 20 ∼ 30% of total skin friction at Reτ ≃ 2000. Application of all the
three approaches consistently reveals that the largest amount of skin friction is generated
by the self-similar motions populating the logarithmic region. It is further shown that
the contribution of these motions to turbulent skin friction gradually increases with the
Reynolds number, and that these coherent structures are eventually responsible for most
of turbulent skin-friction generation at sufficiently high Reynolds numbers.
energy-containing motions in the form of Townsend’s attached eddies in wallbounded
turbulent flows, their role in turbulent skin-friction generation is currently
known very little. In this paper, the contribution of each of these self-similar energycontaining
motions to turbulent skin friction is explored up to Reτ ≃ 4000. Three
different approaches are employed to quantify the skin-friction generation by the motions,
the spanwise length scale of which is smaller than a given cut-off wavelength: 1) FIK
identity in combination with the spanwise wavenumber spectra of the Reynolds shear
stress; 2) confinement of the spanwise computational domain; 3) artificial damping of
the motions to be examined. The near-wall motions are found to continuously lose their
role in skin-friction generation on increasing the Reynolds number, consistent with the
previous finding at low Reynolds numbers. The largest structures given in the form of
very-large-scale and large-scale motions are also found to be of limited importance: due
to a non-trivial scale-interaction process, their complete removal yields only 5 ∼ 8% of
skin-friction reduction at all the Reynolds numbers considered, although they are found
to be responsible for 20 ∼ 30% of total skin friction at Reτ ≃ 2000. Application of all the
three approaches consistently reveals that the largest amount of skin friction is generated
by the self-similar motions populating the logarithmic region. It is further shown that
the contribution of these motions to turbulent skin friction gradually increases with the
Reynolds number, and that these coherent structures are eventually responsible for most
of turbulent skin-friction generation at sufficiently high Reynolds numbers.
Date Issued
2016-12-10
Date Acceptance
2016-10-09
Citation
Journal of Fluid Mechanics, 2016, 808, pp.511-538
ISSN
1469-7645
Publisher
Cambridge University Press (CUP)
Start Page
511
End Page
538
Journal / Book Title
Journal of Fluid Mechanics
Volume
808
Copyright Statement
© 2016 Cambridge University Press. This paper has been accepted for publication and will appear in a revised form, subsequent to peer-review and/or editorial input by Cambridge University Press. Journal of Fluid Mechanics: https://doi.org/10.1017/jfm.2016.665
Sponsor
Engineering and Physical Sciences Research Council
Engineering & Physical Science Research Council (EPSRC)
Identifier
https://www.cambridge.org/core/journals/journal-of-fluid-mechanics/article/skinfriction-generation-by-attached-eddies-in-turbulent-channel-flow/41EACC90D8139214012C7FD1F26E4969
Grant Number
EP/N019342/1
EP/N019342/1
Subjects
Science & Technology
Technology
Physical Sciences
Mechanics
Physics, Fluids & Plasmas
Physics
turbulence simulation
turbulence theory
turbulent boundary layers
DIRECT NUMERICAL-SIMULATION
OSCILLATORY WALL-MOTION
DRAG-REDUCTION
COHERENT STRUCTURES
LOGARITHMIC REGION
SCALE STRUCTURES
BOUNDARY-LAYERS
SHEAR-STRESS
FLUCTUATIONS
STATISTICS
Fluids & Plasmas
01 Mathematical Sciences
09 Engineering
Publication Status
Published
Date Publish Online
2016-11-03