Francesca Chillà (Laboratoire de Physique, École Normale Supérieure de Lyon). Interaction between large and small scales in turbulent thermal convection.

Turbulent thermal convection is complex problem, the flow is forced at almost all scales because of the presence of both large scale circulation and small scales plumes. Moreover the difference of density induced by temperature add an ingredient in the basic equations, so that turbulence could be different from the mechanical forced one. Mixing is in principle different and probably increased by the structure of the plumes. Moreover the entire flow is not homogeneous (at least at large scales) and the statical behavior can be influenced by the large scale flow. Moreover plumes can influence the large scales flow.
Several points of view can be used to study the interaction. One way is to rough plates to increase the injection of thermal plumes. The other way is to use a lagrangian point of view, measuring, for example, lagrangian transport of velocity and temperature, or heat flux and acceleration.
Because of the difficulty of the problem, these studies are presently in development.
I will present some experimental results obtained at the Laboratoire de Physique of the Ens Lyon.