Dynamics of the large-scale circulation in high-Prandtl-number turbulent thermal convection
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AbstractWe report experimental investigations of the dynamics of the large-scale circulation (LSC) in turbulent Rayleigh-Benard convection at high Prandtl number Pr = 19.4 (and also Pr = 7.8) and Rayleigh number Ra varying from 8.3 x 10(8) to 2.9 x 10(11) in a cylindrical convection cell with aspect ratio unity. The dynamics of the LSC is measured using the multithermal probe technique. Both the sinusoidal-fitting (SF) and the temperature-extrema-extraction (TEE) methods are used to analyse the properties of the LSC. It is found that the LSC in high-Pr regime remains a single-roll structure. The azimuthal motion of the LSC is a diffusive process, which is the same as those for Pr around 1. However, the azimuthal diffusion of the LSC, characterized by the angular speed Omega is almost two orders of magnitude smaller when compared with that in water. The non-dimensional time-averaged amplitude of the angular speed T-d (T-d = L-2/kappa is the thermal diffusion time) of the LSC at the mid-height of the convection cell increases with R a as a power law, which is T-d alpha Ra-0.36 +/- 0.01. The Re number based on the oscillation frequency of the LSC is found to scale with Ra as Re = 0.13Ra(0.43 +/- 0.01). It is also found that the normalized flow strength /Delta T x Ra/Pr alpha Re-1.5 +/- 0.1, with the exponent in good agreement with that predicted by Brown & Ahlers (Phys. Fluids, vol. 20, 2008, p. 075101). A wealth of dynamical features of the LSC, such as the cessations, flow reversals, flow mode transitions, torsional and sloshing oscillations are observed in the high-Pr regime as well.
All Author(s) ListXie YC, Wei P, Xia KQ
Journal nameJournal of Fluid Mechanics
Volume Number717
PublisherCambridge University Press (CUP): STM Journals
Pages322 - 346
LanguagesEnglish-United Kingdom
KeywordsBenard convection; plumes/thermals; turbulent convection
Web of Science Subject CategoriesMechanics; MECHANICS; Physics; Physics, Fluids & Plasmas; PHYSICS, FLUIDS & PLASMAS

Last updated on 2020-29-07 at 01:30