Transition on local temperature fluctuations in highly turbulent convection

¹  Institut Néel, CNRS/UJF - BP 166, F-38042 Grenoble cedex 9, France, EU
²  Technische Universität Ilmenau - Ehrenbergstraße 29, D-98693 Ilmenau, Germany, EU

Received: 15 April 2009
Accepted: 13 August 2009

Abstract

In 1997, a new turbulent regime has been observed in a Rayleigh-Bénard cell and has been interpreted as the “Ultimate Regime” of convection. This observation was based on global heat transfer measurements at very high Rayleigh numbers (Ra). Using a set-up similar to the one used in 1997, we examine the signature of this regime from within the flow itself. A systematic study of probe-size corrections shows that the earlier local temperature measurements within the flow were altered by an excessive size of thermometer, but not according to a theoretical model proposed in the literature. Using a probe one order of magnitude smaller than the one used previously, we find evidence that the transition to the very-high-Ra regime is indeed accompanied with a clear change in the statistics of temperature fluctuations in the flow.