TY - JOUR

T1 - Effect of aspect ratio on vortex distribution and heat transfer in rotating Rayleigh-Bénard convection

AU - Stevens, Richard J.A.M.

AU - Overkamp, Jim

AU - Lohse, Detlef

AU - Clercx, Herman J.H.

PY - 2011

Y1 - 2011

N2 - 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=2.91×10^8 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=2.91×10^8. 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.

AB - 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=2.91×10^8 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=2.91×10^8. 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.

KW - IR-78796

KW - METIS-279835

KW - EC Grant Agreement nr.: FP7/222919

KW - EWI-21189

U2 - 10.1103/PhysRevE.84.056313

DO - 10.1103/PhysRevE.84.056313

M3 - Article

VL - 84

JO - Physical review E: covering statistical, nonlinear, biological, and soft matter physics

JF - Physical review E: covering statistical, nonlinear, biological, and soft matter physics

SN - 2470-0045

IS - 5

M1 - 056313

ER -