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


Stevens, Richard J.A.M. and Overkamp, Jim and Lohse, Detlef and Clercx, Herman J.H. (2011) Effect of aspect ratio on vortex distribution and heat transfer in rotating Rayleigh-Bénard convection. Physical Review E: Statistical, nonlinear, and soft matter physics, 84 (5). 056313. ISSN 1539-3755

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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=2.91×108 up to Ra=4.52×109. 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=2.91×108. 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.

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Copyright:© 2011 American Physical Society
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Link to this item:http://purl.utwente.nl/publications/78796
Official URL:http://dx.doi.org/10.1103/PhysRevE.84.056313
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