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Turbulence intensity in wall-bounded and wall-free flows

Turbulence intensity in wall-bounded and wall-free flows
Turbulence intensity in wall-bounded and wall-free flows

Turbulence intensity variations in the outer region of turbulent shear flows are considered, in the context of the diagnostic plot first introduced by Alfredsson et al. (Phys. Fluids, vol. 23, 2011, 041702) and for both (smooth and rough) wall-bounded flows and classical free shear flows. With U Udefined as the mean velocity within the flow, U e  Ueas a suitable reference velocity and u ′  u′as the root mean square of the fluctuating velocity, it is demonstrated that, for wall flows, the attached eddy hypothesis yields a closely linear diagnostic plot ( u ′ /U u′/Uversus U/U e  U/Ue) over a certain Reynolds number range, explaining why the relation seems to work well for both boundary layers and channels despite its lack of any physical basis (Castro et al., J. Fluid Mech., vol. 727, 2013, pp. 119–131). It is shown that mixing layers, jets and wakes also exhibit linear variations of u ′ /U u′/Uversus U/U e  U/Ueover much of the flows (starting roughly from where the turbulence production is a maximum), with slopes of these variations determined by the total mean strain rate, characterised by Townsend’s flow constant R s  Rs. The diagnostic plot thus has a wider range of applicability than might have been anticipated.

shear layer turbulence, turbulent boundary layers, wakes/jets
0022-1120
289-304
Castro, Ian P.
66e6330d-d93a-439a-a69b-e061e660de61
Castro, Ian P.
66e6330d-d93a-439a-a69b-e061e660de61

Castro, Ian P. (2015) Turbulence intensity in wall-bounded and wall-free flows. Journal of Fluid Mechanics, 770, 289-304. (doi:10.1017/jfm.2015.168).

Record type: Article

Abstract

Turbulence intensity variations in the outer region of turbulent shear flows are considered, in the context of the diagnostic plot first introduced by Alfredsson et al. (Phys. Fluids, vol. 23, 2011, 041702) and for both (smooth and rough) wall-bounded flows and classical free shear flows. With U Udefined as the mean velocity within the flow, U e  Ueas a suitable reference velocity and u ′  u′as the root mean square of the fluctuating velocity, it is demonstrated that, for wall flows, the attached eddy hypothesis yields a closely linear diagnostic plot ( u ′ /U u′/Uversus U/U e  U/Ue) over a certain Reynolds number range, explaining why the relation seems to work well for both boundary layers and channels despite its lack of any physical basis (Castro et al., J. Fluid Mech., vol. 727, 2013, pp. 119–131). It is shown that mixing layers, jets and wakes also exhibit linear variations of u ′ /U u′/Uversus U/U e  U/Ueover much of the flows (starting roughly from where the turbulence production is a maximum), with slopes of these variations determined by the total mean strain rate, characterised by Townsend’s flow constant R s  Rs. The diagnostic plot thus has a wider range of applicability than might have been anticipated.

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More information

Accepted/In Press date: 12 March 2015
e-pub ahead of print date: 31 March 2015
Published date: May 2015
Keywords: shear layer turbulence, turbulent boundary layers, wakes/jets
Organisations: Aeronautics, Astronautics & Comp. Eng

Identifiers

Local EPrints ID: 382866
URI: http://eprints.soton.ac.uk/id/eprint/382866
ISSN: 0022-1120
PURE UUID: 7c0971d2-5277-421d-814b-6c108b77ea80

Catalogue record

Date deposited: 03 Nov 2015 15:47
Last modified: 06 Aug 2019 18:36

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