Entropyconserving Scheme for Modeling Nonthermal Energies in Fluid Dynamics Simulations
Abstract
We compare the performance of energybased and entropyconserving schemes for modeling nonthermal energy components, such as unresolved turbulence and cosmic rays, using idealized fluid dynamics tests and isolated galaxy simulations. While both methods are aimed to model advection and adiabatic compression or expansion of different energy components, the energybased scheme numerically solves the nonconservative equation for the energy density evolution, while the entropyconserving scheme uses a conservative equation for modified entropy. Using the standard shock tube and Zel'dovich pancake tests, we show that the energybased scheme results in a spurious generation of nonthermal energy on shocks, while the entropyconserving method evolves the energy adiabatically to machine precision. We also show that, in simulations of an isolated L _{⋆} galaxy, switching between the schemes results in ≈20%30% changes of the total star formation rate and a significant difference in morphology, particularly near the galaxy center. We also outline and test a simple method that can be used in conjunction with the entropyconserving scheme to model the injection of nonthermal energies on shocks. Finally, we discuss how the entropyconserving scheme can be used to capture the kinetic energy dissipated by numerical viscosity into the subgrid turbulent energy implicitly, without explicit source terms that require calibration and can be rather uncertain. Our results indicate that the entropyconserving scheme is the preferred choice for modeling nonthermal energy components, a conclusion that is equally relevant for Eulerian and movingmesh fluid dynamics codes.
 Publication:

The Astrophysical Journal Supplement Series
 Pub Date:
 August 2022
 DOI:
 10.3847/15384365/ac69e1
 arXiv:
 arXiv:2107.14240
 Bibcode:
 2022ApJS..261...16S
 Keywords:

 Hydrodynamical simulations;
 Galaxy evolution;
 Stellar feedback;
 Interstellar dynamics;
 Cosmic rays;
 Shocks;
 767;
 594;
 1602;
 839;
 329;
 2086;
 Astrophysics  Astrophysics of Galaxies;
 Astrophysics  High Energy Astrophysical Phenomena;
 Astrophysics  Instrumentation and Methods for Astrophysics;
 Physics  Computational Physics
 EPrint:
 19 pages + appendix, 10 figures