An Extension of the Athena++ Framework for General Equations of State. (arXiv:1909.05274v1 [astro-ph.IM])

An Extension of the Athena++ Framework for General Equations of State. (arXiv:1909.05274v1 [astro-ph.IM])
<a href="http://arxiv.org/find/astro-ph/1/au:+Coleman_M/0/1/0/all/0/1">Matthew S. B. Coleman</a>

We present modifications to the Athena++ framework to enable use of general
equations of state (EOS). Part of our motivation for doing so is to model
transient astrophysics phenomena, as these types of events are often not well
approximated by an ideal gas. This necessitated changes to the Riemann solvers
implemented in Athena++. We discuss the adjustments made to the HLLC, and HLLD
solvers and EOS calls required for arbitrary EOS. For the first time, we
demonstrate the reliability of our code in a number of tests which utilize a
relatively simple, but non-trivial EOS based on hydrogen ionization,
appropriate for the transition from atomic to ionized hydrogen. Additionally,
we perform tests using an electron-positron Helmholtz EOS, appropriate for
regimes where nuclear statistical equilibrium is a good approximation. These
new complex EOS tests overall show that our modifications to Athena++
accurately solve the Riemann problem with the expected linear convergence. We
provide our test solutions as a means to check the accuracy of other
hydrodynamic codes. Our tests and additions to Athena++ will enable further
research into (magneto)hydrodynamic problems where realistic treatments of the
EOS are required.

We present modifications to the Athena++ framework to enable use of general
equations of state (EOS). Part of our motivation for doing so is to model
transient astrophysics phenomena, as these types of events are often not well
approximated by an ideal gas. This necessitated changes to the Riemann solvers
implemented in Athena++. We discuss the adjustments made to the HLLC, and HLLD
solvers and EOS calls required for arbitrary EOS. For the first time, we
demonstrate the reliability of our code in a number of tests which utilize a
relatively simple, but non-trivial EOS based on hydrogen ionization,
appropriate for the transition from atomic to ionized hydrogen. Additionally,
we perform tests using an electron-positron Helmholtz EOS, appropriate for
regimes where nuclear statistical equilibrium is a good approximation. These
new complex EOS tests overall show that our modifications to Athena++
accurately solve the Riemann problem with the expected linear convergence. We
provide our test solutions as a means to check the accuracy of other
hydrodynamic codes. Our tests and additions to Athena++ will enable further
research into (magneto)hydrodynamic problems where realistic treatments of the
EOS are required.

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