Comment on “Evolution of wall shear stress with Reynolds number in fully developed turbulent channel flow experiments”

Direct numerical simulation of a fully developed turbulent channel flow has been carried out at three Reynolds numbers, 180, 395, and 640, based on the friction velocity and the channel half width, in order to investigate very large-scale structures and their effects on the wall shear-stress fluctuations. It is shown that very large-scale structures exist in the outer layer and that they certainly contribute to inner layer structures at high Reynolds number. Moreover, it is revealed that very large-scale structures exist even in the wall shear-stress fluctuations at high Reynolds number, which are essentially associated with the very large-scale structures in the outer layer.

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Wall shear stress modulation in unsteady turbulent channel flow with high imposed frequencies

Physics of Fluids A Fluid Dynamics ◽

10.1063/1.858538 ◽

1993 ◽

Vol 5 (8) ◽

pp. 2028-2037 ◽

Cited By ~ 41

Author(s):

F. Sedat Tardu ◽

Gilbert Binder

Keyword(s):

Shear Stress ◽

Wall Shear Stress ◽

Channel Flow ◽

Turbulent Channel Flow ◽

Wall Shear

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Simultaneous Stereo PIV and MPS3 Wall-Shear Stress Measurements in Turbulent Channel Flow

Optics ◽

10.3390/opt1010004 ◽

2020 ◽

Vol 1 (1) ◽

pp. 40-51

Author(s):

Esther Mäteling ◽

Michael Klaas ◽

Wolfgang Schröder

Keyword(s):

Shear Stress ◽

Wall Shear Stress ◽

Channel Flow ◽

Inclination Angle ◽

Large Scale ◽

Turbulent Channel Flow ◽

Two Dimensional ◽

Velocity Fluctuations ◽

Wall Shear ◽

Near Wall

An extended experimental method is presented in which the micro-pillar shear-stress sensor (MPS 3 ) and high-speed stereo particle-image velocimetry measurements are simultaneously performed in turbulent channel flow to conduct concurrent time-resolved measurements of the two-dimensional wall-shear stress (WSS) distribution and the velocity field in the outer flow. The extended experimental setup, which involves a modified MPS 3 measurement setup and data evaluation compared to the standard method, is presented and used to investigate the footprint of the outer, large-scale motions (LSM) onto the near-wall small-scale motions. The measurements were performed in a fully developed, turbulent channel flow at a friction Reynolds number R e τ = 969 . A separation between large and small scales of the velocity fluctuations and the WSS fluctuations was performed by two-dimensional empirical mode decomposition. A subsequent cross-correlation analysis between the large-scale velocity fluctuations and the large-scale WSS fluctuations shows that the streamwise inclination angle between the LSM in the outer layer and the large-scale footprint imposed onto the near-wall dynamics has a mean value of Θ ¯ x = 16.53 ∘ , which is consistent with the literature relying on direct numerical simulations and hot-wire anemometry data. When also considering the spatial shift in the spanwise direction, the mean inclination angle reduces to Θ ¯ x z = 13.92 ∘ .

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