Self-organisation and non-linear dynamics in driven magnetohydrodynamic turbulent flows

TL;DR

This paper uses direct numerical simulations to show that magnetohydrodynamic turbulent flows with non-helical forcing can self-organize into laminar helical states, influenced by external force correlation times, impacting turbulence statistics and relevant for plasma and astrophysics.

Contribution

It reveals how non-helical forcing in MHD turbulence leads to self-organized helical states, controlled by external force correlation times, affecting turbulence behavior and statistical measurements.

Findings

Flows self-organize into laminar helical states despite non-helical forcing.

Correlation time of external forces determines the duration of self-organized states.

Time-averaged statistics are significantly influenced by the system's state durations.

Abstract

Magnetohydrodynamic turbulent flows driven by random mechanical and electromagnetic external forces of zero helicities are investigated by means of direct numerical simulations. It is shown that despite the absence of helicities in the forcing, the system is attracted to self-organized helical states that exhibit laminar behaviour despite the large value of the Reynolds numbers examined. We demonstrate that the correlation time of the external forces is controlling the time spent on these states, i.e. for short correlation times the system remains in the turbulent state while as the correlation time is increased the system spends more and more time in the self-organised states. As a result, time averaged statistics can significantly be affected by the time spent on these states. These results have important theoretical implications for the understanding of the suppression of non-linearities in plasma fusion devises as well as in astrophysical observations.