Turbulence in electromagnetically-driven Keplerian flows

TL;DR

This paper experimentally investigates turbulence in electrically driven Keplerian flows, revealing a new turbulent regime with large fluctuations, a Keplerian profile, and complex cascade behaviors, relevant to astrophysical disk dynamics.

Contribution

It introduces the first experimental observation of turbulence regimes in electromagnetically-driven Keplerian flows, including a fully turbulent state with cascade phenomena and large-scale condensates.

Findings

Identification of a fully turbulent regime with Keplerian rotation profile

Observation of energy cascades characteristic of thin layer turbulence

Detection of a bifurcation to quasi-bidimensional flow with large-scale condensate

Abstract

The flow of an electrically conducting fluid in a thin disc under the action of an azimuthal Lorentz force is studied experimentally. At small forcing, the Lorentz force is balanced by either viscosity or inertia, yielding quasi-Keplerian velocity profiles. For very large current and moderate magnetic field, we observe a new regime, fully turbulent, which exhibits large fluctuations and a Keplerian mean rotation profile $\Omega\sim \frac{\sqrt{IB}}{r^{3/2}}$. In this turbulent regime, the dynamics is typical of thin layer turbulence, characterized by a direct cascade of energy towards the small scales and an inverse cascade to large scale. Finally, at very large magnetic field, this turbulent flow bifurcates to a quasi-bidimensional turbulent flow involving the formation of a large scale condensate in the horizontal plane. These results are well understood as resulting from an instability of the B\"odewadt-Hartmann layers at large Reynolds number and discussed in the framework of similar astrophysical flows.