Reversals of the large-scale circulation in quasi-2D Rayleigh–Bénard convection. (4th August 2015)

• Record Type: Journal Article
• Authors: Ni, Rui; Huang, Shi-Di; Xia, Ke-Qing
• Is Part Of: Journal of fluid mechanics. Volume 778(2015:Sep.)
• Publication Date: 2015-08-04
• Subjects: Bénard convection, -- plumes/thermals, -- turbulent convection; Fluid mechanics -- Periodicals; 532.005
• DOI: 10.1017/jfm.2015.433
• Languages: English
• ISSNs: 0022-1120

Abstract

Abstract : We report an experimental study of the large-scale circulation (LSC) reversal in quasi-2D turbulent thermal convection, in which the aspect ratio ${\it\Gamma}$ ( $=\text{height}/\text{length}$ of a rectangular box) is used as a parameter to perturb the stability of the LSC. It is found that the mean time interval $\langle {\it\tau}\rangle$ between two successive reversals increases strongly with increasing ${\it\Gamma}$ . A stochastic model is proposed to incorporate the effect of the corner rolls. In the model, the aspect ratio serves as a tuning parameter for the relative weight of the corner rolls that damp the LSC. The model predictions for the shape of the bistable states of the system and $\langle {\it\tau}\rangle$ agree excellently with the experimental results, with $\langle {\it\tau}\rangle$ having an unexpected stretched exponential Rayleigh number dependence, ${\sim}\!\exp (Ra^{{\it\alpha}})$ . We further show quantitatively that the main damping force of the LSC in a quasi-2D system is from the corner rolls rather than the viscous drag from the sidewalls, which bridges the difference found in quasi-2D and 3D systems.