Journal Article

FZJ-2026-03013

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png No sustained mean velocity in the boundary region of plane thermal convection

Samuel, R. J. ; Bode, M.FZJ* ; Scheel, J. D. ; Sreenivasan, K. R. ; Schumacher, J. (Corresponding author)

2024
Cambridge Univ. Press Cambridge [u.a.]

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Please use a persistent id in citations: doi:10.1017/jfm.2024.853  doi:10.34734/FZJ-2026-03013

Abstract: We study the dynamics of thermal and momentum boundary regions in three-dimensionaldirect numerical simulations of Rayleigh–Bénard convection for the Rayleigh-numberrange $105 ≤ Ra ≤ 1011$ and $Pr = 0.7$. Using a Cartesian slab with horizontal periodicboundary conditions and an aspect ratio of 4, we obtain statistical homogeneity in thehorizontal x- and y-directions, thus approximating best an extended convection layerrelevant for most geo- and astrophysical flow applications. We observe upon canonical useof combined long-time and area averages, with averaging periods of at least 100 free-falltimes, that a global coherent mean flow is practically absent and that the magnitude ofthe velocity fluctuations is larger than the mean by up to 2 orders of magnitude. Thevelocity field close to the wall is a collection of differently oriented local shear-dominatedflow patches interspersed by extensive shear-free incoherent regions which can be aslarge as the whole cross-section, unlike for a closed cylindrical convection cell of aspectratio of the order 1. The incoherent regions occupy a 60 % area fraction for all Rayleighnumbers investigated here. Rather than resulting in a pronounced mean flow with smallfluctuations about such a mean, as found in small-aspect-ratio convection, the velocityfield is dominated by strong fluctuations of all three components around a non-existent orweak mean. We discuss the consequences of these observations for convection layers withlarger aspect ratios, including boundary layer instabilities and the resulting turbulent heattransport.

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Contributing Institute(s):

1. Jülich Supercomputing Center (JSC)

Research Program(s):

1. 5112 - Cross-Domain Algorithms, Tools, Methods Labs (ATMLs) and Research Groups (POF4-511) (POF4-511)
2. MesoComp - Order at the Mesoscale: Connecting supercomputing of compressible convection to classical and quantum machine learning (101052786) (101052786)
3. Novel System Architectures Design (NOVAS)

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Database coverage:
; ; ; Clarivate Analytics Master Journal List ; Current Contents - Engineering, Computing and Technology ; Current Contents - Physical, Chemical and Earth Sciences ; Essential Science Indicators ; IF < 5 ; JCR ; Nationallizenz ; SCOPUS ; Science Citation Index Expanded ; Web of Science Core Collection

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