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Turbulent channel flow over an anisotropic porous wall - drag increase and reduction
KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre.
KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre.
2018 (English)In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 842, p. 381-394Article in journal (Refereed) Published
Abstract [en]

The effect of the variations of the permeability tensor on the close-to-the-wall behaviour of a turbulent channel flow bounded by porous walls is explored using a set of direct numerical simulations. It is found that the total drag can be either reduced or increased by more than 20% by adjusting the permeability directional properties. Drag reduction is achieved for the case of materials with permeability in the vertical direction lower than the one in the wall-parallel planes. This configuration limits the wall-normal velocity at the interface while promoting an increase of the tangential slip velocity leading to an almost 'one-component' turbulence where the low- and high-speed streak coherence is strongly enhanced. On the other hand, strong drag increase is found when high wall-normal and low wall-parallel permeabilities are prescribed. In this condition, the enhancement of the wall-normal fluctuations due to the reduced wall-blocking effect triggers the onset of structures which are strongly correlated in the spanwise direction, a phenomenon observed by other authors in flows over isotropic porous layers or over ribletted walls with large protrusion heights. The use of anisotropic porous walls for drag reduction is particularly attractive since equal gains can be achieved at different Reynolds numbers by rescaling the magnitude of the permeability only.

Place, publisher, year, edition, pages
Cambridge University Press, 2018. Vol. 842, p. 381-394
Keywords [en]
drag reduction, mixing enhancement, turbulence simulation
National Category
Other Physics Topics
Identifiers
URN: urn:nbn:se:kth:diva-225188DOI: 10.1017/jfm.2018.152ISI: 000427267100001OAI: oai:DiVA.org:kth-225188DiVA, id: diva2:1194609
Funder
Swedish Research Council, 2014-5001Swedish e‐Science Research Center
Note

QC 20180403

Available from: 2018-04-03 Created: 2018-04-03 Last updated: 2018-04-03Bibliographically approved

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Rosti, Marco E.Brandt, Luca
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