Ultimate regimes of turbulent convection in nonideal fluids revisited

Rayleigh-Bénard convection (RBC) at high Rayleigh (Ra) numbers represents perhaps the most important model system to study heat and momentum transport by turbulent convection. Experiments reaching very high Ra, approaching values relevant for convective systems in Nature (like the flows in Earth's atmosphere or oceans), were performed using various working fluids, like cryogenic helium 4, or sulphur hexafluoride, in different laboratories, and provide unique insights into the dynamics of this `archetype of complex dynamical systems''. Nevertheless, the experiments up to this date lack unambiguous interpretation. The current project addresses the notorious difficulties of experimental distinction of transfer enhancement in the high-Ra regimes of RBC as being due to either hydrodynamic, thermodynamic (fluid property) or geometric (aspect ratio) factors. We propose here a systematic statistical analysis of data from (existing and new) experiments and numerical simulations, supported by interpretation by Grossmann-Lohse-type models.