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Outer layer turbulence intensities in smooth- and rough-wall boundary layers

Outer layer turbulence intensities in smooth- and rough-wall boundary layers
Outer layer turbulence intensities in smooth- and rough-wall boundary layers
Clear differences in turbulence intensity profiles in smooth, transitional and fully rough zero-pressure-gradient boundary layers are demonstrated, using the diagnostic plot introduced by Alfredsson, Segalini & Örlü (Phys. Fluids, vol. 23, 2011, p. 041702) – u?/U versus U/Ue, where u? and U are the local (root mean square) fluctuating and mean velocities and Ue is the free stream velocity. A wide range of published data are considered and all zero-pressure-gradient boundary layers yield outer flow u?/U values that are roughly linearly related to U/Ue, just as for smooth walls, but with a significantly higher slope which is completely independent of the roughness morphology. The difference in slope is due largely to the influence of the roughness parameter (?U+ in the usual notation) and all the data can be fitted empirically by using a modified form of the scaling, dependent only on ?U/Ue. The turbulence intensity, at a location in the outer layer where U/Ue is fixed, rises monotonically with increasing ?U/Ue which, however, remains of O(1) for all possible zero-pressure-gradient rough-wall boundary layers even at the highest Reynolds numbers. A measurement of intensity at a point in the outer region of the boundary layer can provide an indication of whether the surface is aerodynamically fully rough, without having to determine the surface stress or effective roughness height. Discussion of the implication for smooth/rough flow universality of differences in outer-layer mean velocity wake strength is included
0022-1120
119-131
Castro, Ian P.
66e6330d-d93a-439a-a69b-e061e660de61
Segalini, Antoni
99c2765e-2f5e-43f3-a2f2-ef0572052bad
Alfredsson, Henrik
e3e00627-5498-4862-911e-ec78105e8f16
Castro, Ian P.
66e6330d-d93a-439a-a69b-e061e660de61
Segalini, Antoni
99c2765e-2f5e-43f3-a2f2-ef0572052bad
Alfredsson, Henrik
e3e00627-5498-4862-911e-ec78105e8f16

Castro, Ian P., Segalini, Antoni and Alfredsson, Henrik (2013) Outer layer turbulence intensities in smooth- and rough-wall boundary layers. Journal of Fluid Mechanics, 727, 119-131. (doi:10.1017/jfm.2013.252).

Record type: Article

Abstract

Clear differences in turbulence intensity profiles in smooth, transitional and fully rough zero-pressure-gradient boundary layers are demonstrated, using the diagnostic plot introduced by Alfredsson, Segalini & Örlü (Phys. Fluids, vol. 23, 2011, p. 041702) – u?/U versus U/Ue, where u? and U are the local (root mean square) fluctuating and mean velocities and Ue is the free stream velocity. A wide range of published data are considered and all zero-pressure-gradient boundary layers yield outer flow u?/U values that are roughly linearly related to U/Ue, just as for smooth walls, but with a significantly higher slope which is completely independent of the roughness morphology. The difference in slope is due largely to the influence of the roughness parameter (?U+ in the usual notation) and all the data can be fitted empirically by using a modified form of the scaling, dependent only on ?U/Ue. The turbulence intensity, at a location in the outer layer where U/Ue is fixed, rises monotonically with increasing ?U/Ue which, however, remains of O(1) for all possible zero-pressure-gradient rough-wall boundary layers even at the highest Reynolds numbers. A measurement of intensity at a point in the outer region of the boundary layer can provide an indication of whether the surface is aerodynamically fully rough, without having to determine the surface stress or effective roughness height. Discussion of the implication for smooth/rough flow universality of differences in outer-layer mean velocity wake strength is included

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Published date: July 2013
Organisations: Aerodynamics & Flight Mechanics Group

Identifiers

Local EPrints ID: 354304
URI: http://eprints.soton.ac.uk/id/eprint/354304
ISSN: 0022-1120
PURE UUID: 5e9accbc-53df-45f0-b77b-6791ea71c935

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Date deposited: 08 Jul 2013 08:53
Last modified: 14 Mar 2024 14:16

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Contributors

Author: Ian P. Castro
Author: Antoni Segalini
Author: Henrik Alfredsson

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