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Astrophysics, Gravitation and Cosmology Seminar - Philipp Grete (Universität Hamburg) "As a matter of dynamical range – scale-dependent energy dynamics in magnetized turbulence and pushing simulation limits"

Event Type
Department of Physics
Loomis 464
Oct 12, 2022   12:00 pm  
Philipp Grete
Brandy Koebbe
Originating Calendar
Physics - Astrophysics, Relativity, and Cosmology Seminar

Magnetized turbulence is ubiquitous in many astrophysical and terrestrial plasmas but no universal theory exists. Even the detailed energy dynamics in magnetohydrodynamic turbulence are still not well understood. We present a suite of subsonic, super-Alfvénic, high plasma-beta MHD turbulence simulation that only vary in their dynamical range, i.e., in their separation between the large-scale forcing and dissipation scales. From a practical point of view, we show how numerical dissipation can be estimated using an energy transfer analysis framework and that implicit large eddy simulations match direct numerical simulations. From a theoretical point of view, we use the same framework to demonstrate that – contrary to hydrodynamic turbulence – the cross-scale energy fluxes are not constant in MHD turbulence. This applies both to different mediators (such as cascade processes or magnetic tension) for a given dynamical range as well as to a dependence on the dynamical range itself. We do not observe any indication of convergence even at the highest resolution simulation at 2048^3 cells.

This raises the question on whether an asymptotic regime in MHD turbulence exists, and, if yes, what it looks like. Finally, to tackle this question in the future we will introduce Parthenon (a performance portable adaptive mesh refinement framework) and AthenaPK (the MHD application code on top), which recently reached 92% weak scaling parallel efficiency on 73,728 GPUs on Frontier (the first TOP500 exascale supercomputer).

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