Vortex development behind a finite porous obstruction in a channel
Name
Nepf_Vortex development.pdf
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1.76 MB
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Adobe PDF
Checksum (MD5)
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Author(s)
Zong, Lijun
Nepf, Heidi
Date Issued
December 2011
Journal
Journal of Fluid Mechanics
Publisher
Cambridge University Press
Citation
Zong, Lijun, and Heidi Nepf. “Vortex Development Behind a Finite Porous Obstruction in a Channel.” Journal of Fluid Mechanics 691 (2011): 368–391. © Cambridge University Press 2011
Version
Final published version
Abstract
This experimental study describes the turbulent wake behind a two-dimensional porous obstruction, consisting of a circular array of cylinders. The cylinders extend from the channel bed through the water surface, mimicking a patch of emergent vegetation. Three patch diameters (D) and seven solid volume fractions (Φ) are tested. Because flow can pass through the patch, directly downstream there is a region of steady, non-zero, streamwise velocity, U[subscript 1], called the steady wake. For the patch diameters and solid volume fractions considered here, U[subscript 1] is a function of Φ only. The length of the steady wake (L[subscript 1]) increases as Φ decreases and can be predicted from the growth of a plane shear layer. The formation of the von-Kármán vortex street is delayed until the end of the steady wake. There are two regions of elevated transverse velocity fluctuation (v[subscript rms]): directly behind the patch, associated with the wake turbulence of individual cylinders; and at the distance L[subscript 1] from the patch, associated with the formation of large-scale wake oscillation. Velocity along the centreline of the wake starts to increase only after the patch-scale vortex street is formed, and it approaches the free-stream velocity over a distance L[subscript 2]. The dimensionless length of the entire wake, L[subscript 1] + L[subscript 2]/ D[subscript 1], increases with patch porosity.
MIT Department
Massachusetts Institute of Technology. Department of Civil and Environmental Engineering
Terms of Use
Article is made available in accordance with the publisher's policy and may be subject to US copyright law. Please refer to the publisher's site for terms of use.
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DOI of Published Version
https://doi.org/10.1017/jfm.2011.479
