Search for the "ultimate state" in turbulent Rayleigh-B\'enard convection

TL;DR

This study measures heat transfer and temperature variations in turbulent Rayleigh-Bénard convection over a wide range of Rayleigh numbers, finding no evidence of the transition to an 'ultimate regime' as previously reported.

Contribution

It provides extensive experimental data on turbulent convection at high Rayleigh numbers, challenging prior claims of an 'ultimate regime' transition.

Findings

No observed transition to the 'ultimate regime' in the measured data.

Results are consistent with Niemela et al.'s measurements.

Data covers a broad range of Prandtl numbers and pressures.

Abstract

Measurements of the Nusselt number $Nu$ and of temperature variations $\Delta T_b$ in the bulk fluid are reported for turbulent Rayleigh-B\'enard convection of a cylindrical sample. They cover the Rayleigh-number range $10^{9} \alt Ra \alt 3\times 10^{14}$ using He (Prandtl number $Pr = 0.67$), N$_2$ ($Pr = 0.72$) and SF$_6$ ($Pr = 0.79$ to 0.84) at pressures up to 15 bars and near-ambient temperatures. The sample had a height $L=2.24$m and diameter $D = 1.12$m and was located in a new High-Pressure Convection Facility (HPCF) at the Max Planck Institute for Dynamics and Self-Organization in G\"ottingen, Germany. The data do not show the transition to an "ultimate regime" reported by Chavanne et al. and are consistent with the measurements of Niemela et al.