Title : Radiative heating as a gateway to the fully turbulent regimes of convection
Contact : Nicolas Mordant
Abstract : Every abstract about convection has to start with this mandatory sentence: convection is ubiquitous in nature as it drives winds in the atmosphere, currents in the ocean, generates magnetic fields inside astrophysical objects and triggers supernova explosions.
In this talk, we will focus on rotating and non rotating convection forced by a radiative heat source. Radiative heating is relevant to stellar and planetary interiors, where the main question is to quantify the transport of heat and tracers by turbulent convection, including the crucial impact of global rotation. The observation of fully turbulent regimes, known as the « ultimate regime » and the « geostrophic turbulence regime » for non rotating and rotating convection, respectively, has remained a challenge in the literature where the standard configuration of the experiments leads to systems constrained by the existence of boundary layers, hence preventing the observation of those extreme regimes, predicted more than 40 years ago.
After a quick introduction to turbulent convection studies, I will show how we can realize radiatively driven convection in the laboratory by using a powerful spotlight shining at a tank filled with a mixture of water and carbon black dye, and how it can bypass the constraining boundary layers. I will then provide experimental and numerical evidences that radiative forcing led to the first clear experimental observation of a fully turbulent regime of convection, with and without rotation.
