24/02/2015 - Nathaniel Baker (Coventry University & CRETA-LNCMI)
Turbulence displays radically opposite dynamics whether it is three-dimensional (3D) or two-dimensionnal (2D). The former is characterized by a direct energy cascade where energy transits from the injection scale down to the small dissipative scales, while the latter features an inverse energy cascade characterized by energy moving up from the injection scale to the larger scales. The goal of this project is to study the dynamics of a turbulent flow, which features at the same time
scales that are "topologically" 2D and 3D, and see how its dynamics is impacted by no-slip boundaries. This problem is tackled within the framework of low-Rm magnetohydrodynamics (MHD), which is particularly suited in this case. Indeed, one of the main features of low-Rm MHD is the diffusion of momentum by the Lorentz force along the magnetic field.
In this talk, we will discuss how the topological dimensionality of a low-Rm MHD flow confined between two walls depends on the the diffusion length associated to the rotational part of the Lorentz force, and how it can introduce three-dimensionality in the case of a weakly inertial flow. The experimental setup that is used to investigate fully turbulent flows will also be presented.