Universal scaling laws in turbulent Rayleigh-Bénard convection with and without roughness
Résumé
Experimental heat-transfer measurements published in the literature seem to be contradictory, some showing a transition at Ra≈1011, some showing a delayed transition at higher Ra, or no transition at all. New experimental and numerical heat-flux and velocity measurements, both reaching Ra up to \num{e12}, are reported on a wide range of operating conditions.
In the new measurements in the rough cell which reaches Rayleigh numbers, Ra, up to 2.5e12, the Nusselt number show a clear Ra1/2 scaling, hinting a fully turbulent regime. In contrast to the Nu vs Ra relationship, we evidence that the dimensionless heat-flux, expressed as RaNu, recovers a universal scaling with Reynolds number, collapses all data and highlights a universal critical Reynolds number.
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