Ultimate-state scaling in a shell model for homogeneous turbulent convection
Publication in refereed journal

香港中文大學研究人員

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摘要An interesting question in turbulent convection is how the heat transport depends on the strength of thermal forcing in the limit of very large thermal forcing. Kraichnan predicted [Phys. Fluids 5, 1374 (1962) ] that for fluids with low Prandtl number (Pr), the heat transport measured by the Nusselt number (Nu) would depend on the strength of thermal forcing measured by the Rayleigh number (Ra) as Nu similar to Ra(1/2) with logarithmic corrections at very high Ra. According to Kraichnan, the shear boundary layers play a crucial role in giving rise to this so-called ultimate-state scaling. A similar scaling result is predicted by the Grossmann-Lohse theory [J. Fluid Mech. 407, 27 (2000)], but with the assumption that the ultimate state is a bulk- dominated state in which both the average kinetic and thermal dissipation rates are dominated by contributions from the bulk of the flow with the boundary layers either broken down or playing no role in the heat transport. In this paper, we study the dependence of Nu and the Reynolds number (Re) measuring the root-mean-squared velocity fluctuations on Ra and Pr, for low Pr, using a shell model for homogeneous turbulent convection where buoyancy is acting directly on most of the scales. We find that Nu similar to Ra(1/2)Pr(1/2) and Re similar to Ra(1/2)Pr(-1/2), which resemble the ultimatestate scaling behavior for fluids with low Pr, and show that the presence of a drag acting on the large scales is crucial in giving rise to such scaling. As a large-scale drag cannot exist by itself in the bulk of turbulent thermal convection, our results indicate that if buoyancy acts on most of the scales in the bulk of turbulent convection at very high Ra, then the ultimate state cannot be bulk dominated.
著者Ching ESC, Ko TC
期刊名稱Physical Review E
出版年份2008
月份9
日期1
卷號78
期次3
出版社American Physical Society
國際標準期刊號1539-3755
電子國際標準期刊號1550-2376
語言英式英語
Web of Science 學科類別Physics; Physics, Fluids & Plasmas; PHYSICS, FLUIDS & PLASMAS; Physics, Mathematical; PHYSICS, MATHEMATICAL

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