title: Effect of aspect ratio on vortex distribution and heat transfer in rotating Rayleigh-Bénard convection.
abstract: Numerical and experimental data for the heat transfer as a function of the Rossby number Ro in turbulent rotating Rayleigh-Bénard convection are presented for the Prandtl number Pr=4.38 and the Rayleigh number Ra=2.91×10(8) up to Ra=4.52×10(9). The aspect ratio Γ≡D/L, where L is the height and D the diameter of the cylindrical sample, is varied between Γ=0.5 and 2.0. Without rotation, where the aspect ratio influences the global large-scale circulation, we see a small-aspect-ratio dependence in the Nusselt number for Ra=2.91×10(8). However, for stronger rotation, i.e., 1/Ro>>1/Ro(c), the heat transport becomes independent of the aspect ratio. We interpret this finding as follows: In the rotating regime the heat is mainly transported by vertically aligned vortices. Since the vertically aligned vortices are local, the aspect ratio has a negligible effect on the heat transport in the rotating regime. Indeed, a detailed analysis of vortex statistics shows that the fraction of the horizontal area that is covered by vortices is independent of the aspect ratio when 1/Ro>>1/Ro(c). In agreement with the results of Weiss et al. [Phys. Rev. Lett. 105, 224501 (2010)], we find a vortex-depleted area close to the sidewall. Here we show that there is also an area with enhanced vortex concentration next to the vortex-depleted edge region and that the absolute widths of both regions are independent of the aspect ratio.
authors.affiliation: Department of Science and Technology, University of Twente, Enschede, The Netherlands.
authors.forename: Richard J A M
authors.initials: RJ
authors.lastname: Stevens
authors.forename: Jim
authors.initials: J
authors.lastname: Overkamp
authors.forename: Detlef
authors.initials: D
authors.lastname: Lohse
authors.forename: Herman J H
authors.initials: HJ
authors.lastname: Clercx
mesh_terms: D001696:Biomechanical Phenomena; D003198:Computer Simulation; D018481:Convection; D004735:Energy Transfer; D006112:Gravitation; D006358:Hot Temperature; D015233:Models, Statistical; D008962:Models, Theoretical; D010825:Physics / Q000379:methods*; D013696:Temperature