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  Azimuthal diffusion of the large-scale-circulation plane, and absence of significant non-Boussinesq effects, in turbulent convection near the ultimate-state transition.

He, X., Bodenschatz, E., & Ahlers, G. (2016). Azimuthal diffusion of the large-scale-circulation plane, and absence of significant non-Boussinesq effects, in turbulent convection near the ultimate-state transition. Journal of Fluid Mechanics, 791: R3. doi:10.1017/jfm.2016.56.

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Item Permalink: http://hdl.handle.net/11858/00-001M-0000-002A-297A-3 Version Permalink: http://hdl.handle.net/11858/00-001M-0000-002D-3DE4-9
Genre: Journal Article

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 Creators:
He, X.1, Author              
Bodenschatz, E.1, Author              
Ahlers, G.1, Author              
Affiliations:
1Laboratory for Fluid Dynamics, Pattern Formation and Biocomplexity, Max Planck Institute for Dynamics and Self-Organization, Max Planck Society, ou_2063287              

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Free keywords: Bénard convection; Turbulent convection
 Abstract: We present measurements of the orientation θ0 and temperature amplitude δ of the large-scale circulation in a cylindrical sample of turbulent Rayleigh–Bénard convection (RBC) with aspect ratio Γ≡D/L=1.00 (D and L are the diameter and height respectively) and for the Prandtl number Pr≃0.8. The results for θ0 revealed a preferred orientation with up-flow in the west, consistent with a broken azimuthal invariance due to the Earth’s Coriolis force (see Brown & Ahlers (Phys. Fluids, vol. 18, 2006, 125108)). They yielded the azimuthal diffusivity Dθ and a corresponding Reynolds number Reθ for Rayleigh numbers over the range 2×1012≲Ra≲1.5×1014. In the classical state (Ra≲2×1013) the results were consistent with the measurements by Brown & Ahlers (J. Fluid Mech., vol. 568, 2006, pp. 351–386) for Ra≲1011 and Pr=4.38, which gave Reθ∝Ra0.28, and with the Prandtl-number dependence Reθ∝Pr−1.2 as found previously also for the velocity-fluctuation Reynolds number ReV (He et al., New J. Phys., vol. 17, 2015, 063028). At larger Ra the data for Reθ(Ra) revealed a transition to a new state, known as the ‘ultimate’ state, which was first seen in the Nusselt number Nu(Ra) and in ReV(Ra) at Ra∗1≃2×1013 and Ra∗2≃8×1013. In the ultimate state we found Reθ∝Ra0.40±0.03. Recently, Skrbek & Urban (J. Fluid Mech., vol. 785, 2015, pp. 270–282) claimed that non-Oberbeck–Boussinesq effects on the Nusselt and Reynolds numbers of turbulent RBC may have been interpreted erroneously as a transition to a new state. We demonstrate that their reasoning is incorrect and that the transition observed in the Göttingen experiments and discussed in the present paper is indeed to a new state of RBC referred to as ‘ultimate’.

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Language(s): eng - English
 Dates: 2016-02-172016-03
 Publication Status: Published in print
 Pages: -
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 Table of Contents: -
 Rev. Method: Peer
 Identifiers: DOI: 10.1017/jfm.2016.56
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Title: Journal of Fluid Mechanics
Source Genre: Journal
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Pages: 13 Volume / Issue: 791 Sequence Number: R3 Start / End Page: - Identifier: -