Large-Eddy Simulations of Magnetohydrodynamic Turbulence in Heliophysics and Astrophysics

TL;DR

This paper reviews the current state of Large Eddy Simulation modeling for magnetohydrodynamic turbulence in space physics and astrophysics, emphasizing the challenges of representing subgrid scales and magnetic effects.

Contribution

It provides a comprehensive overview of LES/SGS modeling techniques for MHD turbulence, highlighting recent advances and future research directions in heliophysics and astrophysics.

Findings

Summarizes the nature of MHD turbulence and energy dissipation processes.

Discusses how magnetic fields influence turbulence modeling.

Assesses the successes and challenges of current LES approaches in astrophysical contexts.

Abstract

We live in an age in which high-performance computing is transforming the way we do science. Previously intractable problems are now becoming accessible by means of increasingly realistic numerical simulations. One of the most enduring and most challenging of these problems is turbulence. Yet, despite these advances, the extreme parameter regimes encountered in space physics and astrophysics (as in atmospheric and oceanic physics) still preclude direct numerical simulation. Numerical models must take a Large Eddy Simulation (LES) approach, explicitly computing only a fraction of the active dynamical scales. The success of such an approach hinges on how well the model can represent the subgrid-scales (SGS) that are not explicitly resolved. In addition to the parameter regime, heliophysical and astrophysical applications must also face an equally daunting challenge: magnetism. The presence of magnetic fields in a turbulent, electrically conducting fluid flow can dramatically alter the coupling between large and small scales, with potentially profound implications for LES/SGS modeling. In this review article, we summarize the state of the art in LES modeling of turbulent magnetohydrodynamic (MHD) flows. After discussing the nature of MHD turbulence and the small-scale processes that give rise to energy dissipation, plasma heating, and magnetic reconnection, we consider how these processes may best be captured within an LES/SGS framework. We then consider several specific applications in heliophysics and astrophysics, assessing triumphs, challenges, and future directions.