Effect of aspect ratio on vortex distribution and heat transfer in rotating Rayleigh-Benard convection

Numerical and experimental data for the heat transfer as a function of the Rossby number Ro in turbulent rotating Rayleigh-Benard convection are presented for the Prandtl number Pr = 4.38 and the Rayleigh number Ra = 2.91 x 10(8) up to Ra = 4.52 x 10(9). The aspect ratio Gamma equivalent to 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 Ra = 2.91 x 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.