On the 2D behavior of 3D MHD with a strong guiding field

TL;DR

This study uses direct numerical simulations to explore how a strong guiding magnetic field influences the two-dimensional and three-dimensional behaviors of magneto-hydrodynamic flows, revealing inverse cascades and anisotropic effects.

Contribution

It demonstrates the conditions under which a strong magnetic field induces 2D behavior and inverse energy cascades in MHD turbulence, highlighting the effects of various forcing parameters.

Findings

Large-scale flow becomes 2D with inverse cascade under strong magnetic field

Small scales exhibit 3D MHD cascading behavior

Anisotropic forcing induces inverse cascade in parallel direction

Abstract

The Magneto-hydrodynamic (MHD) equations in the presence of a guiding magnetic field are investigated by means of direct numerical simulations. The basis of the investigation consists of 9 runs forced at the small scales. The results demonstrate that for a large enough uniform magnetic field the large scale flow behaves as a two dimensional (non-MHD) fluid exhibiting an inverse cascade of energy in the direction perpendicular to the magnetic field, while the small scales behave like a three dimensional MHD-fluid cascading the energy forwards. The amplitude of the inverse cascade is sensitive to the magnetic field amplitude, the domain size, the forcing mechanism, and the forcing scale. All these dependencies are demonstrated by the varying parameters of simulations. Furthermore, in the case that the system is forced anisotropically in the small parallel scales an inverse cascade in the parallel direction is observed that is feeding the 2D modes.