Quantifying energetics and dissipation in magnetohydrodynamic turbulence

Abstract

We perform a suite of two- and three-dimensional magnetohydrodynamic (MHD) simulations with the Athena code of the non-driven Kelvin-Helmholtz instability in the subsonic, weak magnetic field limit. Focusing the analysis on the non-linear turbulent regime, we quantify energy transfer on a scale-by-scale basis and identify the physical mechanisms responsible for energy exchange by developing the diagnostic known as spectral energy transfer function analysis. At late times when the fluid is in a state of MHD turbulence, magnetic tension mediates the dominant mode of energy injection into the magnetic reservoir, whereby turbulent fluid motions twist and stretch the magnetic field lines. This generated magnetic energy turbulently cascades to smaller scales, while being exchanged backwards and forwards with the kinetic energy reservoir, until finally being dissipated. Incorporating explicit dissipation pushes the dissipation scale to larger scales than if the dissipation were entirely numerical. For scales larger than the dissipation scale, we show that the physics of energy transfer in decaying MHD turbulence is robust to numerical effects.

23 pages, 20 figures, 4 tables, Accepted for publication in MNRAS

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• Energy dynamics and current sheet structure in fluid and kinetic simulations of decaying magnetohydrodynamic turbulence
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• Exact relations for energy transfer in self-gravitating isothermal turbulence
• Extension of the sub-grid-scale gradient model for compressible magnetohydrodynamics turbulent instabilities
• Impact of magneto-rotational instability on grain growth in protoplanetary disks: I. Relevant turbulence properties
• Global simulations of magnetorotational turbulence II: turbulent energetics
• As A Matter of State: The role of thermodynamics in magnetohydrodynamic turbulence
• Nonlinear mode coupling and energetics of driven magnetized shear-flow turbulence
• Magnetising galaxies with cold inflows
• Scale-by-scale energy transfers in bubbly flows