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2.8 Some caveats with hydrocodes

2.8.1 Consistent advection of chemical abundances grid codes

See dedicated consistent advection section.

2.8.2 Variable adiabatic index

KROME is internally using a variable adiabatic index, consistent with the chemical abundances, density and temperature of a given cell in the code. For consistency, the fluid dynamics code should likewise support a variable adiabatic index. At the very least, authors using KROME should record the adiabatic indices that are output from KROME and adapt a reasonable compromise for the external adiabatic index used in e.g. the Riemann solver in a supporting finite volume code.

Having a variable adiabatic index also implies that the conversion from internal energy to pressure and temperature is non-trivial. In codes that consistently uses an equation of state module, this may be a simple change, while for codes that computes pressures and temperatures inline all over the code it is more involved and may require many changes throughout the code base.

More details on the adiabatic index calculation here.