Flow organisation in laterally unconfined Rayleigh–Bénard turbulence

Alexander Blass, Roberto Verzicco, Detlef Lohse, Richard J. A. M. Stevens, Dominik Krug*

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

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We investigate the large-scale circulation (LSC) of turbulent Rayleigh–Bénard convection in a large box of aspect ratio Γ=32Γ=32 for Rayleigh numbers up to Ra=109Ra=109 and at a fixed Prandtl number Pr=1Pr=1 . A conditional averaging technique allows us to extract statistics of the LSC even though the number and the orientation of the structures vary throughout the domain. We find that various properties of the LSC obtained here, such as the wall-shear stress distribution, the boundary layer thicknesses and the wind Reynolds number, do not differ significantly from results in confined domains ( Γ≈1Γ≈1 ). This is remarkable given that the size of the structures (as measured by the width of a single convection roll) more than doubles at the highest RaRa as the confinement is removed. An extrapolation towards the critical shear Reynolds number of Recrits≈420Rescrit≈420 , at which the boundary layer (BL) typically becomes turbulent, predicts that the transition to the ultimate regime is expected at Racrit≈O(1015)Racrit≈O(1015) in unconfined geometries. This result is in line with the Göttingen experimental observations (He et al., Phys. Rev. Lett., vol. 108, 2012, 024502; New J. Phys., vol. 17, 2015, 063028). Furthermore, we confirm that the local heat transport close to the wall is highest in the plume impacting region, where the thermal BL is thinnest, and lowest in the plume emitting region, where the thermal BL is thickest. This trend, however, weakens with increasing RaRa .
Original languageEnglish
Article numberA26
JournalJournal of fluid mechanics
Early online date16 Nov 2020
Publication statusPublished - 10 Jan 2021


  • atmospheric flows
  • Rayleigh-Bénard convection
  • turbulent convection
  • Rayleigh-Benard convection
  • UT-Hybrid-D


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