Application of the diffusing wave spectroscopy to the study of boundary layers in turbulent convection

Full description

Turbulent thermal convection is one of the driving forces behind most geo- and astrophysical flows, so it’s vital to account for it accurately in climate models. It is also involved in many industrial processes. It is therefore important to know whether the heat transport laws obtained in well-controlled laboratory experiments can be transposed to natural flows, where the scales are much larger. Indeed, transport efficiency can be strongly affected by the nature of the boundary layers, which can differ greatly in these different flows. It is therefore important to gain a better understanding of the nature of these boundary layers, and of the transfer processes at their level. There are theories, for example, that the fraction of energy dissipated in the boundary layers has an impact on the overall heat flux transported from the hot wall to the cold wall. The aim of this internship is to set up a device enabling the first experimental measurement of the energy dissipated in the boundary layers of turbulent convection in the Rayleigh-Bénard configuration.

To estimate the energy dissipated, we need to be able to measure the norm of the velocity gradient. This quantity is difficult to obtain with conventional anemometry techniques, which measure velocity fields with limited resolution. These gradients are also costly to obtain numerically over long time scales. But we have developed a technique for directly measuring the norm of velocity gradients using the Diffusing Wave Spectroscopy. We have already qualified this method on model flows and successfully applied it to turbulent flows. This has enabled us to study the dynamics of dissipative structures at the wall of a turbulent flow. In convection, it will enable us to measure the dissipative structures and the dissipated energy rate in order to estimate the nature of the boundary layers (laminar or turbulent?) as a function of the forcing.

The internship will take place within the SPEC SPHYNX team at CEA-Saclay, where we are interested in the fundamental aspects of turbulence and their application to geophysical flows.

Location

CEA-Saclay, (91) Essonne, France

Internship conditions

• Internship duration: 6 months
• Level of study: Bac+5
• Training: Master 2
• Continuation in PhD thesis: Yes
• Application deadline: January 2025, 10^th

Supervisor

Sébastien Aumaître
Phone: 01 69 08 74 37
Email :