[FLASH-USERS] Error of physical units in the eos_idealGamma implementation

[acreyes acreyes]

Hi Gabriel,

"eos_singleSpeciesA" is a runtime parameter so you can specify its value
inside of your "flash.par" to match the physics of the gas you're
simulating as well as the system of units for your simulation. You may
verify that it changes in your simulation from the default value by
checking the "*.log".

Adam

On Mon, Feb 15, 2021 at 5:57 AM RIGON Gabriel <gabriel.rigon at nagoya-u.jp>
wrote:

> Hi,
>
> I found what seems to be an error in the eos_idealGamma subroutine
> (physics/Eos/EosMain/Gamma/eos_idealGamma.F90).
>
> In the case of (mode == MODE_DENS_TEMP), the energy is defined as :
> Eint = Na k / (gamma - 1) * T / A
> this is the same formula as the one in the user guide - formula 16.6  p.236
>
> If we look at its units, we have :
> Na k : in cm^2 g / (s^2 K mol)
> T : in Kelvin
> Eint : in cm^2 / s^2
> so A should be in g / mol
> According to the user guide: "A is the average atomic mass", actually it
> should be the average molar mass (but the value is the same in cgs).
>
> The problem here is the actual definition of A in the code.
> A is defined using the eos_singleSpeciesA variable which is initialized
> in rp_initParameters to a dimensionless constant "1". The problem is the
> absence of dimension.
> If you choose to change your units system with "pc_unitsbase" going from
> CGS to MKS (in PhysicalConstant), the value of Na and k will change as
> well as the unit of Eint but not the unit of A. As a results you will
> obtain a Eint 10^3 to low compare to its actual value.
>
> Best regards,
> Gabriel Rigon
>
> --
> Gabriel Rigon
> Laboratory for Theoretical Astronomy & Astrophysics (TA-Lab)
> Graduate School of Science
> Division of Particle and Astrophysical Science
> Nagoya University, Japan
>
>
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