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The spatial structure of the logarithmic region in very-high-Reynolds-number rough wall turbulent boundary layers

Published online by Cambridge University Press:  26 October 2018

Michael Heisel Open the ORCID record for Michael Heisel [Opens in a new window] ,
Teja Dasari ,
Yun Liu ,
Jiarong Hong Open the ORCID record for Jiarong Hong [Opens in a new window] ,
Filippo Coletti  and
Michele Guala
Michael Heisel*
Affiliation:
St Anthony Falls Laboratory, University of Minnesota, Minneapolis, MN 55414, USA Department of Civil, Environmental, and Geo- Engineering, University of Minnesota, Minneapolis, MN 55455, USA
Teja Dasari
Affiliation:
St Anthony Falls Laboratory, University of Minnesota, Minneapolis, MN 55414, USA Department of Mechanical Engineering, University of Minnesota, Minneapolis, MN 55455, USA
Yun Liu
Affiliation:
Department of Mechanical and Civil Engineering, Purdue University Northwest, Westville, IN 46391, USA
Jiarong Hong
Affiliation:
St Anthony Falls Laboratory, University of Minnesota, Minneapolis, MN 55414, USA Department of Mechanical Engineering, University of Minnesota, Minneapolis, MN 55455, USA
Filippo Coletti
Affiliation:
St Anthony Falls Laboratory, University of Minnesota, Minneapolis, MN 55414, USA Department of Aerospace Engineering and Mechanics, University of Minnesota, Minneapolis, MN 55455, USA
Michele Guala
Affiliation:
St Anthony Falls Laboratory, University of Minnesota, Minneapolis, MN 55414, USA Department of Civil, Environmental, and Geo- Engineering, University of Minnesota, Minneapolis, MN 55455, USA
*
†Email address for correspondence: heise070@umn.edu
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Abstract

Using super-large-scale particle image velocimetry (SLPIV), we investigate the spatial structure of the near-wall region in the fully rough atmospheric surface layer with Reynolds number $Re_{\unicode[STIX]{x1D70F}}\sim O(10^{6})$. The field site consists of relatively flat, snow-covered farmland, allowing for the development of a fully rough turbulent boundary layer under near-neutral thermal stability conditions. The imaging field of view extends from 3 m to 19 m above the ground and captures the top of the roughness sublayer and the bottom of an extensive logarithmic region. The SLPIV technique uses natural snowfall as seeding particles for the flow imaging. We demonstrate that SLPIV provides reliable measurements of first- and second-order velocity statistics in the streamwise and wall-normal directions. Our results in the logarithmic region show that the structural features identified in laboratory studies are similarly present in the atmosphere. Using instantaneous vector fields and two-point correlation analysis, we identify vortex structures sharing the signature of hairpin vortex packets. We also evaluate the zonal structure of the boundary layer by tracking uniform momentum zones (UMZs) and the shear interfaces between UMZs in space and time. Statistics of the UMZs and shear interfaces reveal the role of the zonal structure in determining the mean and variance profiles. The velocity difference across the shear interfaces scales with the friction velocity, in agreement with previous studies, and the size of the UMZs scales with wall-normal distance, in agreement with the attached eddy framework.

JFM classification

Geophysical and Geological Flows: Atmospheric flows Boundary Layers: Boundary layer structure Turbulent Flows: Turbulent boundary layers
Type
JFM Papers
Information
Journal of Fluid Mechanics , Volume 857 , 25 December 2018 , pp. 704 - 747
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Copyright
© 2018 Cambridge University Press 

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Heisel et al. supplementary movie

Time evolution of the vortex structure highlighted in figure 6 of the article. (left) Velocity vector field overlaid on the PIV images. The listed convective velocity is subtracted from the vectors. (middle) Color plot of the streamwise velocity. (right) Color plot of the swirling strength for vortices tracked using the methodology described in Appendix A.

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