[FLASH-USERS] questions on RHD solver

[Salvatore Cielo]

Dear FLASH users,

I have been having a look for the first time at the RHD split hydro
solver (in FLASH 4.2.2)  with the relativsitic ideal gamma EOS, and I
have a few questions that maybe you can answer.
I would like to simulate astrophysical relativistic jets, but so far I
have not used the RHD in a setup of mine, I just had a look at the
source code.

The Eos_wrapped subroutine seems to still use the non-relativistic
definitions of internal energy and kinetic energy, in sharp contrast
with what is reported in the user guide (eqs. 14.13-14.16).
(the Eos itself is still the same as the classic ideal gamma).

Also, it seems to accept only the MODE_DENS_EI, while the user guide
reports that MODE_DENS_PRES should be allowed too (page 210, sec.
14.2.3).
Actually Eos_wrapped calculates the internal energy from density and
pressure, so it does not make a big difference. I am fine with this
approach, but it could be a bit cleaner.

My question is: is it supposed to work like that? Are the density and
internal energy that the hydro solver expects to find still the ones
with the non-relativistic definition?
If not, it will be better to implement eq. 14.13 and 14.14 (3) for the
energy, as for instance is done in the Simulation_initBlock of the
RHD_riemann2D test problem.

Then, that energy  in eq. 14.14 contains a term proportional to
density * lorentz_gamma^2. That should be kinetic+rest-mass energy.
But as it is, it seems to contain an extra lorentz factor.
This should depend on whether FLASH is using the proper relativistic
"specific" energy density or something else (not really clear from the
RHD section of the user guide)...

I will now take a look at the hydro solver source code to find out,
but if someone has already some experience with it, any advice will be
appreciated!

Thank you very much!

Best regards,

Salvatore
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Salvatore Cielo

Max-Planck-Institute for Astronomy
Koenigstuhl 17
D-69117 Heidelberg

Tel.: (++49|0) 6221 - 528-203
E-mail:  cielo at mpia.de
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