Effect of aspectratio on vortex distribution and heat transfer in rotating Rayleigh-Bénard convection

Numerical and experimental data for the heat transfer as function of the Rossby number Ro in rotating Rayleigh-Benard are presented for Pr = 4.38 and up to Ra = 4.52 × 109 . The aspect ratio is varied between G = 0.5 and G = 2.0. Without rotation, where the aspect ratio influences the global flow structure, we see a small aspect-ratio dependence in the Nusselt number. For stronger rotation, i.e. 1/Ro 1/Roc, 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 these vortices are local, the aspect ratio has a negligible effect on the heat transport in the rotating regime. Indeed, an analysis of the vortex statistics shows that the fraction of the horizontal area that is covered by vortices is aspect-ratio independent when 1/Ro 1/Roc. In agreement with the results of Weiss & Ahlers (2011) 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.