Numerous natural systems organise into a turbulent layer adjacent to a stably stratified one: examples include stellar interiors divided into a convective zone and a radiative zone, and lower planetary atmospheres divided into a troposphere and a stratosphere. Capturing the coupled dynamics of such systems and understanding the exchanges of energy and momentum at the interface between the two layers are challenging, because of the large range of involved time- and length-scales: indeed, the rapid small-scale turbulence excites waves at intermediate scale, which propagate and interact non-linearly to generate mixing and largescale circulations. It is thus a highly complex fluid mechanics problem that pushes towards the limit of theoretical and numerical modelling.
In this context, model laboratory experiments are extremely useful in deciphering the various ongoing processes, because they naturally englobe all scales without relying on simplification or hypothesis for closure. I will present the results of experimental investigations of two idealised configurations: a turbulent jet impinging a density interface with the associated mixing mechanism, and the convection in water around its density maximum at 4 degree Celsius. I will review our recent progress in terms of wave excitation and selection, as well as in terms of their non-linear interactions. Consequences for climate and stellar modelling will also be discussed.
Organizer: Matteo BUGLI
Local contact: Thierry FOGLIZZO