Large-scale flow modes in turbulent Rayleigh-Bénard convection

Abstract eng:
The modes of the global flow structure in turbulent Rayleigh-B´enard convection in air (P r = 0.7) at various aspect ratios between 1 ≤ Γ ≤ 4 were studied experimentally. By the use of an infrared camera, high resolution distributions of the local wall heat flux at the surface of the heated bottom plate were measured. The data reveals a spot of enhanced heat flux, which is correlated to the down-welling motion of the fluid. Based on this, the position of the large-scale vortex can be identified. Varying the height of the fluid layer, a critical aspect ratios of Γcrit = 1.65 was found for the transition from a single vortex to a double vortex structure, which agrees very well with previous experimental and numerical investigations if one takes into account a Rayleigh number dependency of that quantity.

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