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On the decay of dispersive motions in the outer region of rough-wall boundary layers

On the decay of dispersive motions in the outer region of rough-wall boundary layers
On the decay of dispersive motions in the outer region of rough-wall boundary layers
In rough-wall boundary layers, wall-parallel non-homogeneous mean-flow solutions existthat lead to so-called dispersive velocity components and dispersive stresses. They play asignificant role in the mean-flow momentum balance near the wall, but typically disappearin the outer layer. A theoretical framework is presented to study the decay of dispersivemotions in the outer layer. To this end, the problem is formulated in Fourier space,and a set of governing ordinary differential equations per mode in wavenumber space isderived by linearizing the Reynolds-averaged Navier–Stokes equations around a constantbackground velocity. With further simplifications, analytically tractable solutions arefound consisting of linear combinations of exp(−kz) and exp(−Kz), with z the walldistance, k the magnitude of the horizontal wavevector k, and where K(k, Re) is afunction of k and the Reynolds number Re. Moreover, for k → ∞ or k1 → 0 (withk1 the stream-wise wavenumber), K → k is found, in which case solutions consist of alinear combination of exp(−kz) and z exp(−kz), and are Reynolds number independent.These analytical relations are compared in the limit of k1 = 0 to the rough boundarylayer experiments by Vanderwel and Ganapathisubramani (J. Fluid Mech. 774, R2, 2015)and are in reasonable agreement for `k/δ 6 0.5, with δ the boundary-layer thickness and 'k = 2π/k.
0022-1120
1-13
Meyers, Johan
0e2a737d-b393-43b2-8e55-e6829fd6e25e
Ganapathisubramani, Bharathram
5e69099f-2f39-4fdd-8a85-3ac906827052
Cal, Raul Bayoan
d864c46a-9df6-4ad7-bcbc-a7543e48d52f
Meyers, Johan
0e2a737d-b393-43b2-8e55-e6829fd6e25e
Ganapathisubramani, Bharathram
5e69099f-2f39-4fdd-8a85-3ac906827052
Cal, Raul Bayoan
d864c46a-9df6-4ad7-bcbc-a7543e48d52f

Meyers, Johan, Ganapathisubramani, Bharathram and Cal, Raul Bayoan (2019) On the decay of dispersive motions in the outer region of rough-wall boundary layers. Journal of Fluid Mechanics, 862, 1-13. (doi:10.1017/jfm.2018.1019).

Record type: Article

Abstract

In rough-wall boundary layers, wall-parallel non-homogeneous mean-flow solutions existthat lead to so-called dispersive velocity components and dispersive stresses. They play asignificant role in the mean-flow momentum balance near the wall, but typically disappearin the outer layer. A theoretical framework is presented to study the decay of dispersivemotions in the outer layer. To this end, the problem is formulated in Fourier space,and a set of governing ordinary differential equations per mode in wavenumber space isderived by linearizing the Reynolds-averaged Navier–Stokes equations around a constantbackground velocity. With further simplifications, analytically tractable solutions arefound consisting of linear combinations of exp(−kz) and exp(−Kz), with z the walldistance, k the magnitude of the horizontal wavevector k, and where K(k, Re) is afunction of k and the Reynolds number Re. Moreover, for k → ∞ or k1 → 0 (withk1 the stream-wise wavenumber), K → k is found, in which case solutions consist of alinear combination of exp(−kz) and z exp(−kz), and are Reynolds number independent.These analytical relations are compared in the limit of k1 = 0 to the rough boundarylayer experiments by Vanderwel and Ganapathisubramani (J. Fluid Mech. 774, R2, 2015)and are in reasonable agreement for `k/δ 6 0.5, with δ the boundary-layer thickness and 'k = 2π/k.

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On the decay of dispersive motions in the outer region of rough - Accepted Manuscript
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Accepted/In Press date: 11 December 2018
e-pub ahead of print date: 25 January 2019
Published date: 10 March 2019

Identifiers

Local EPrints ID: 426776
URI: https://eprints.soton.ac.uk/id/eprint/426776
ISSN: 0022-1120
PURE UUID: e4560967-6bff-4e0f-b291-f2121cd2bab5
ORCID for Bharathram Ganapathisubramani: ORCID iD orcid.org/0000-0001-9817-0486

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Date deposited: 12 Dec 2018 17:30
Last modified: 14 Mar 2019 01:37

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