Numerical and experimental data for the heat transfer as a function of the Rossby number $\text{Ro}$ in turbulent rotating Rayleigh-Bénard convection are presented for the Prandtl number $\text{Pr}=4.38$ and the Rayleigh number $\text{Ra}=2.91\times {10}^8$ up to $\text{Ra}=4.52\times {10}^9$. The aspect ratio $\Gamma \equiv D/L$, where $L$ is the height and $D$ the diameter of the cylindrical sample, is varied between $\Gamma =0.5$ 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 $\text{Ra}=2.91\times {10}^8$. However, for stronger rotation, i.e., $1/\text{Ro}\gg 1/{\text{Ro}}_c$, 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 $1/\text{Ro}\gg 1/{\text{Ro}}_c$. 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.

• Received 23 May 2011

DOI:https://doi.org/10.1103/PhysRevE.84.056313