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

R.J.A.M. Stevens, J.V. Overkamp, D. Lohse, H.J.H. Clercx

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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=2.91×108 up to Ra=4.52×109. The aspect ratio G=D/L, where L is the height and D the diameter of the cylindrical sample, is varied between G=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=2.91×108. However, 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 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/Roc. 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.
Originele taal-2Engels
Pagina's (van-tot)056313-1/10
Aantal pagina's10
TijdschriftPhysical Review E - Statistical, Nonlinear, and Soft Matter Physics
Nummer van het tijdschrift5
StatusGepubliceerd - 2011


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