[FLASH-USERS] How to properly calculate sound speed

[Klaus Weide]

On Wed, 3 Feb 2010, Seyit Hocuk wrote:

> Very basic question maybe, but does one have to use Helmholtz eos to get that
> gamma? 

Seyit,

If you are not using the Helmholtz EOS then I assume you are using either 
the Gamma EOS or the Multigamma EOS.  In both of those cases, the 
adiabatic index gamma already has a well-defined meaning, so it would not 
make sense for the FLASH Eos unit to provide a different (and conflicting)
way to compute gamma.

> Is it simple to switch from multigamma (for multispecies) to Helmholtz
> gamma.

The Helmholtz EOS is quite different from the others, and you cannot in 
general just replace Gamma or Multigamma with Helmholtz in an arbitrary
simulation.  For one thing, temperature and density have to be within
a certain range (e.g., 10^4 K < temperature < 10^{11} K), and you
have to use physically meaningful (cgs) units for your data.

Klaus