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Transfer of mass and momentum at rough and porous surfaces
KTH, School of Engineering Sciences (SCI), Engineering Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.ORCID iD: 0000-0003-3094-0848
KTH, School of Engineering Sciences (SCI), Engineering Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. School of Mechanical Sciences, Indian Institute of Technology Goa, Ponda, 403401, India.
KTH, School of Engineering Sciences (SCI), Engineering Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.ORCID iD: 0000-0003-0229-8878
KTH, School of Engineering Sciences (SCI), Engineering Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.ORCID iD: 0000-0002-8209-1449
2020 (English)In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 884, article id A21Article in journal (Refereed) Published
Abstract [en]

The surface texture of materials plays a critical role in wettability, turbulence and transport phenomena. In order to design surfaces for these applications, it is desirable to characterise non-smooth and porous materials by their ability to exchange mass and momentum with flowing fluids. While the underlying physics of the tangential (slip) velocity at a fluid-solid interface is well understood, the importance and treatment of normal (transpiration) velocity and normal stress is unclear. We show that, when the slip velocity varies at an interface above the texture, a non-zero transpiration velocity arises from mass conservation. The ability of a given surface texture to accommodate a normal velocity of this kind is quantified by a transpiration length. We further demonstrate that normal momentum transfer gives rise to a pressure jump. For a porous material, the pressure jump can be characterised by so-called resistance coefficients. By solving five Stokes problems, the introduced measures of slip, transpiration and resistance can be determined for any anisotropic non-smooth surface consisting of regularly repeating geometric patterns. The proposed conditions are a subset of the effective boundary conditions derived from formal multi-scale expansion. We validate and demonstrate the physical significance of the effective conditions on two canonical problems - a lid-driven cavity and a turbulent channel flow, both with non-smooth bottom surfaces.

Place, publisher, year, edition, pages
Cambridge University Press, 2020. Vol. 884, article id A21
Keywords [en]
porous media, flow-structure interactions
National Category
Mechanical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-266245DOI: 10.1017/jfm.2019.897ISI: 000501702400001OAI: oai:DiVA.org:kth-266245DiVA, id: diva2:1382462
Note

QC 20200103

Available from: 2020-01-03 Created: 2020-01-03 Last updated: 2020-01-03Bibliographically approved

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Lacis, UgisPasche, SimonBagheri, Shervin

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Lacis, UgisSudhakar, Y.Pasche, SimonBagheri, Shervin
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