Absence of evidence for transition to the 'ultimate' regime of Rayleigh-Bénard convection

There are several distinct predictions for the asymptotic behavior of heat transport Nu as the Rayleigh number Ra → ∞ in thermal turbulence described by the fundamental model of Rayleigh-Bénard convection. One is Nu = O(Ra^1/3) and another is the so-called 'ultimate' scaling Nu = O(Ra^1/2) possibly modified by logarithmic corrections to Ra^1/2/(log Ra)^3/2 or Ra^1/2/(log Ra)². Recently reported experimental and direct numerical simulation measurements of Nu as a function of Ra have been cited as evidence of transition to the 'ultimate' state. In this talk, without questioning the veracity of the Nu-Ra data reported therein, we show that the data do not support the claims.