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Friday 18 May 2018[Seminar] Sub-grid Modelling of Compressible Magnetohydrodynamic Turbulence

Dimitar Vlaykov - Max-Planck Goettingen

4th Floor Physics 11:30-12:30

The range of dynamically active scales in astrophysical plasmas can span tens of orders of magnitude. This precludes direct numerical simulations of such systems from ever being a realistic possibility. In large eddy simulations (LES), instead, only the largest scales are directly simulated, while a closure is used to capture the effect of the unresolved physics occurring at the small, sub-grid scales (SGS).

This talk shall address the problem of the SGS closures in the case of compressible magnetohydrodynamic (MHD) turbulence. The performance of a recently developed non-linear SGS closure is compared to a selection of canonical alternatives. The test cases are that of homogeneous and isotropic turbulence, which is statistically stationary (a priori tests) and decaying (a posteriori tests).

It is found that SGS closures in general have a significant effect specifically on high-order statistics of small-scale fields and only when applied to scales above the grid scale. Furthermore, the structural origins of the proposed closure allow it to surpass all examined alternatives in almost all tests.

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