Aspect ratio dependence of heat transfer and large-scale flow in turbulent convection

Original · EN

The heat transport and corresponding changes in the large-scale circulation (LSC) in turbulent Rayleigh-Bénard convection are studied by means of three-dimensional direct numerical simulations as a function of the aspect ratio Γ of a closed cylindrical cell and the Rayleigh number Ra. For small and moderate aspect ratios, the global heat transfer law Nu=A× Raβ shows a power law dependence of both fit coefficients A and β on the aspect ratio. A minimum Nusselt number coincides with the point where the LSC undergoes a transition from a single-roll to a double-roll pattern. With increasing aspect ratio, we detect complex multi-roll LSC configurations. The aspect ratio dependence of the turbulent heat transfer for small and moderate Γ is in line with a varying amount of energy contained in the LSC, as quantified by the Proper Orthogonal Decomposition analysis. For Γ 8 the heat transfer becomes independent of the aspect ratio.