An insight in turbulent thermal convection

Francesca CHILLA

ENS Lyon

The Rayleigh-­‐Bénard convection is in principle one of simplest convective systems to be studied. Turbulent thermal convection is often present in common geophysical or industrial situation, at the same time the turbulent state of Rayleigh Bénard convection is less understood and more difficult to achieve in controlled laboratory condition. To study turbulent state is necessary to explore Rayleigh numbers larger then 106 and several order of magnitude in Ra are necessary. In the last 20 years improvements have be done thanks to new experimental techniques (as PIV measurements) and the use of “exotic fluids” as gases near the critical point that allows to reach Ra=1016. Improvements in computation power also allow presently to run numerical simulations till Ra=1012. Nevertheless lot of points remain unclear, the behaviours of Nusselt number as function of Rayleigh number is not completely elucidated, particularly for Ra>1012. A situation of multistability seems to appear, but the mechanism of selection of every particular state is not clear. The role of the boundary layer and its interaction with the turbulent bulk seems to be key points for the comprehension of the problem. A point will be done on the recent results and present axes of research.



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