Search for the "ultimate state" in turbulent Rayleigh-Bénard convection.

Measurements of the Nusselt number Nu and of temperature variations DeltaTb in the bulk fluid are reported for turbulent Rayleigh-Bénard convection of a cylindrical sample. They cover the Rayleigh-number range 10(9) less than or similar to Ra less than or similar to 3x10(14) using He (Prandtl number Pr=0.67), N2 (Pr=0.72) and SF6 (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 Göttingen, 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.