3D global simulations of RIAFs: convergence, effects of azimuthal extent, and dynamo

Dhang, Prasun and Sharma, Prateek (2019) 3D global simulations of RIAFs: convergence, effects of azimuthal extent, and dynamo. In: MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 482 (1). pp. 848-869.

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Abstract

We study the long-term evolution of non-radiative geometrically thick (H/R approximate to 0.5) accretion flows using 3D global ideal magnetohydrodynamic simulations and a pseudo-Newtonian gravity. We find that resolving the scale height with 42 grid points is adequate to obtain convergence with the product of quality factors similar to << Q(theta)>><< Q(phi)>> >= 300 and magnetic tilt angle theta(B) similar to 13 degrees-14 degrees. Like previous global isothermal thin disc simulations, we find stronger mean magnetic fields for the restricted azimuthal domains. Imposing periodic boundary conditions with the azimuthal extent smaller than 2 pi makes the turbulent field at low m appear as a mean field in the runs with smaller azimuthal extent. But unlike previous works, we do not find a monotonic trend in turbulence with the azimuthal extent. We conclude that the minimum azimuthal extent should be >= pi/2 to capture the flow structure, but a full 2 pi extent is necessary to study the dynamo. We find an intermittent dynamo cycle, with alpha-quenching playing an important role in the non-linear saturated state. Unlike previous local studies, we find almost similar values of kinetic and magnetic alpha-s, giving rise to an irregular distribution of dynamo-alpha. The effects of dynamical quenching are shown explicitly for the first time in global simulations of accretion flows.

Item Type:	Journal Article
Publication:	MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
Publisher:	OXFORD UNIV PRESS
Additional Information:	Copyright of this article belongs to OXFORD UNIV PRESS
Keywords:	accretion; accretion discs; dynamo; instabilities; magnetic fields; MHD; turbulence; methods: numerical
Department/Centre:	Division of Physical & Mathematical Sciences > Joint Astronomy Programme Division of Physical & Mathematical Sciences > Physics
Date Deposited:	29 Jan 2019 08:52
Last Modified:	30 Jan 2019 12:01
URI:	http://eprints.iisc.ac.in/id/eprint/61533

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