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Roughness as a Route to the Ultimate Regime of Thermal Convection
KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
2017 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 118, no 7, 074503Article in journal (Refereed) Published
Abstract [en]

We use highly resolved numerical simulations to study turbulent Rayleigh-Benard convection in a cell with sinusoidally rough upper and lower surfaces in two dimensions for Pr = 1 and Ra = [4 x 10(6), 3 x 10(9)]. By varying the wavelength. at a fixed amplitude, we find an optimal wavelength lambda(opt) for which the Nusselt-Rayleigh scaling relation is (Nu - 1 proportional to Ra-0.483), maximizing the heat flux. This is consistent with the upper bound of Goluskin and Doering [J. Fluid Mech. 804, 370 (2016)] who prove that Nu can grow no faster than O(Ra-1/2) as Ra -> infinity, and thus with the concept that roughness facilitates the attainment of the so-called ultimate regime. Our data nearly achieve the largest growth rate permitted by the bound. When lambda << lambda(opt) and lambda >> lambda(opt), the planar case is recovered, demonstrating how controlling the wall geometry manipulates the interaction between the boundary layers and the core flow. Finally, for each Ra, we choose the maximum Nu among all., thus optimizing over all lambda, to find Nu(opt) - 1 = 0.01xRa(0.444).

Place, publisher, year, edition, pages
American Physical Society, 2017. Vol. 118, no 7, 074503
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-204081DOI: 10.1103/PhysRevLett.118.074503ISI: 000394096000007PubMedID: 28256887Scopus ID: 2-s2.0-85013296222OAI: oai:DiVA.org:kth-204081DiVA: diva2:1085472
Note

QC 20170329

Available from: 2017-03-29 Created: 2017-03-29 Last updated: 2017-03-29Bibliographically approved

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