Three dimensional flow motions in the viscous sublayer

S. Santosh Kumar; Xinyi Huang; Xiang Yang; Jiarong Hong

doi:10.1016/j.taml.2021.100239

Three dimensional flow motions in the viscous sublayer

S. Santosh Kumar, Xinyi Huang, Xiang Yang, Jiarong Hong

Mechanical Engineering

Research output: Contribution to journal › Article › peer-review

3 Scopus citations

Abstract

We employ novel digital Fresnel reflection holography to capture the 3D flows within the viscous sublayer of a smooth-wall turbulent channel flow at Re_τ=400. The measurements reveal unsteady and diverse flow patterns in the sublayer including nearly uniform high and low speed flows and strong small-scale (on the order of viscous wall units) spanwise meandering motions. The probability density functions (PDFs) of wall shear stresses show a clear discrepancy in high stress range with those from direct numerical simulation (DNS), which is attributed to the unresolved streamwise and spanwise motions by DNS. Moreover, the PDF of Lagrangian particle accelerations yields a stretched exponential shape like that in homogenous isotropic turbulence, indicating strong intermittency in the sublayer. We find a significant fraction of high accelerations is associated with the small-scale meandering motions. Our study helps explain the effect of sublayer-scale roughness on reducing drag and flow separation reported in the literature.

Original language	English (US)
Article number	100239
Journal	Theoretical and Applied Mechanics Letters
Volume	11
Issue number	2
DOIs	https://doi.org/10.1016/j.taml.2021.100239
State	Published - Feb 1 2021

Bibliographical note

Funding Information:
Funding for this research was provided by The Office of Naval Research (Grant No. N000141612755). A large part of the computational work was performed using resources at the Minnesota Supercomputing Institute (MSI) at the University of Minnesota ( http://www.msi.umn.edu ) and the Advanced CyberInfrastructure (ACI) at Penn. State which the authors would also like to thank and acknowledge.

Funding Information:
Funding for this research was provided by The Office of Naval Research (Grant No. N000141612755). A large part of the computational work was performed using resources at the Minnesota Supercomputing Institute (MSI) at the University of Minnesota (http://www.msi.umn.edu) and the Advanced CyberInfrastructure (ACI) at Penn. State which the authors would also like to thank and acknowledge.

Publisher Copyright:
© 2021

Keywords

DNS
Digital holography
Meandering motions
Sublayer-scale roughness
Turbulent channel flow
Viscous sublayer

Publisher link

10.1016/j.taml.2021.100239

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abstract = "We employ novel digital Fresnel reflection holography to capture the 3D flows within the viscous sublayer of a smooth-wall turbulent channel flow at Reτ=400. The measurements reveal unsteady and diverse flow patterns in the sublayer including nearly uniform high and low speed flows and strong small-scale (on the order of viscous wall units) spanwise meandering motions. The probability density functions (PDFs) of wall shear stresses show a clear discrepancy in high stress range with those from direct numerical simulation (DNS), which is attributed to the unresolved streamwise and spanwise motions by DNS. Moreover, the PDF of Lagrangian particle accelerations yields a stretched exponential shape like that in homogenous isotropic turbulence, indicating strong intermittency in the sublayer. We find a significant fraction of high accelerations is associated with the small-scale meandering motions. Our study helps explain the effect of sublayer-scale roughness on reducing drag and flow separation reported in the literature.",

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author = "Kumar, {S. Santosh} and Xinyi Huang and Xiang Yang and Jiarong Hong",

note = "Funding Information: Funding for this research was provided by The Office of Naval Research (Grant No. N000141612755). A large part of the computational work was performed using resources at the Minnesota Supercomputing Institute (MSI) at the University of Minnesota ( http://www.msi.umn.edu ) and the Advanced CyberInfrastructure (ACI) at Penn. State which the authors would also like to thank and acknowledge. Funding Information: Funding for this research was provided by The Office of Naval Research (Grant No. N000141612755). A large part of the computational work was performed using resources at the Minnesota Supercomputing Institute (MSI) at the University of Minnesota (http://www.msi.umn.edu) and the Advanced CyberInfrastructure (ACI) at Penn. State which the authors would also like to thank and acknowledge. Publisher Copyright: {\textcopyright} 2021",

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N2 - We employ novel digital Fresnel reflection holography to capture the 3D flows within the viscous sublayer of a smooth-wall turbulent channel flow at Reτ=400. The measurements reveal unsteady and diverse flow patterns in the sublayer including nearly uniform high and low speed flows and strong small-scale (on the order of viscous wall units) spanwise meandering motions. The probability density functions (PDFs) of wall shear stresses show a clear discrepancy in high stress range with those from direct numerical simulation (DNS), which is attributed to the unresolved streamwise and spanwise motions by DNS. Moreover, the PDF of Lagrangian particle accelerations yields a stretched exponential shape like that in homogenous isotropic turbulence, indicating strong intermittency in the sublayer. We find a significant fraction of high accelerations is associated with the small-scale meandering motions. Our study helps explain the effect of sublayer-scale roughness on reducing drag and flow separation reported in the literature.

AB - We employ novel digital Fresnel reflection holography to capture the 3D flows within the viscous sublayer of a smooth-wall turbulent channel flow at Reτ=400. The measurements reveal unsteady and diverse flow patterns in the sublayer including nearly uniform high and low speed flows and strong small-scale (on the order of viscous wall units) spanwise meandering motions. The probability density functions (PDFs) of wall shear stresses show a clear discrepancy in high stress range with those from direct numerical simulation (DNS), which is attributed to the unresolved streamwise and spanwise motions by DNS. Moreover, the PDF of Lagrangian particle accelerations yields a stretched exponential shape like that in homogenous isotropic turbulence, indicating strong intermittency in the sublayer. We find a significant fraction of high accelerations is associated with the small-scale meandering motions. Our study helps explain the effect of sublayer-scale roughness on reducing drag and flow separation reported in the literature.

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Three dimensional flow motions in the viscous sublayer

Abstract

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