grim: A Flexible, Conservative Scheme for Relativistic Fluid Theories
Abstract
Hot, diffuse, relativistic plasmas such as subEddington blackhole accretion flows are expected to be collisionless, yet are commonly modeled as a fluid using ideal general relativistic magnetohydrodynamics (GRMHD). Dissipative effects such as heat conduction and viscosity can be important in a collisionless plasma and will potentially alter the dynamics and radiative properties of the flow from that in ideal fluid models; we refer to models that include these processes as Extended GRMHD. Here we describe a new conservative code, grim, that enables all of the above and additional physics to be efficiently incorporated. grim combines time evolution and primitive variable inversion needed for conservative schemes into a single step using an algorithm that only requires the residuals of the governing equations as inputs. This algorithm enables the code to be physics agnostic as well as flexibility regarding timestepping schemes. grim runs on CPUs, as well as on GPUs, using the same code. We formulate a performance model and use it to show that our implementation runs optimally on both architectures. grim correctly captures classical GRMHD test problems as well as a new suite of linear and nonlinear test problems with anisotropic conduction and viscosity in special and general relativity. As tests and example applications, we resolve the shock substructure due to the presence of dissipation, and report on relativistic versions of the magnetothermal instability and heat flux driven buoyancy instability, which arise due to anisotropic heat conduction, and of the firehose instability, which occurs due to anisotropic pressure (I.e., viscosity). Finally, we show an example integration of an accretion flow around a Kerr black hole, using Extended GRMHD.
 Publication:

The Astrophysical Journal
 Pub Date:
 March 2017
 DOI:
 10.3847/15384357/aa5f55
 arXiv:
 arXiv:1702.01106
 Bibcode:
 2017ApJ...837...92C
 Keywords:

 accretion;
 accretion disks;
 magnetohydrodynamics: MHD;
 plasmas;
 relativistic processes;
 Astrophysics  Instrumentation and Methods for Astrophysics;
 Astrophysics  High Energy Astrophysical Phenomena
 EPrint:
 doi:10.3847/15384357/aa5f55