Experimental study of boundary layers in turbulent convection by Diffusive Waves Spectroscopy

The aim of this thesis is to carry out the first experimental measurement of the energy dissipated in the boundary layers during turbulent convection in the Rayleigh-Bénard configuration. Indeed, some theories assert that this quantity controls the heat flux transported from the hot wall to the cold wall, while the efficiency of turbulent transport in convection is the subject of debate. Yet the properties of turbulent transport are essential to understanding the dynamics of climate and many astrophysical objects.

To estimate the energy dissipated, we need to be able to measure the norm of the velocity gradient. This quantity is difficult to access with conventional anemometry techniques, which measure velocity fields with limited resolution. These gradients are also expensive to obtain numerically over long time scales. But we have developed a technique for directly measuring the norm of velocity gradients using Multiple Scattering Spectroscopy. This will enable us to measure dissipative structures and the rate of energy dissipation in boundary layers.