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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