[JBUNSW]

Dear FOAMers,

I need to know how the density and compressibility are updated in OpenFOAM? The question has a general scope and applies to many compressible thermophysical models and solvers. I divide my question in two parts:

1. In pEqn.H of all compressible solvers (dieselFOAM, sonicFOAM, reactingFOAM, etc.) there is a line that reads

rho = thermo.rho();

I tracked down this rho() function to see how density is calculated. For the compressible thermophysical models, in the base class that is basicPsiThermo.H, one can find this:

             //- Density [kg/m^3] - uses current value of pressure
             virtual tmp<volScalarField> rho() const
             {
                 return p_*psi();
             }

Is my understanding of how rho_ is updated correct?!

2. Assuming that my impression of rho_ calculation is correct, we need to know psi() to find density, that is we need to know the compressibility. This raises two more questions:

2.1 My survey led to the speculation that psi_ is updated in hsPsiThermo.C.

TCells[celli] = mixture_.THs(hsCells[celli], TCells[celli]);
psiCells[celli] = mixture_.psi(pCells[celli], TCells[celli]);

This is true when sensible enthalpy is used as the basis of thermophysical model. For scenarios where h or e are used similar procedure follows. Is my understanding correct?!

2.2 If above is correct, then I need to know how the psi(p, T) works. I could find THs function in specieThermoI.H which basically updates temperature based on a given sensible ehthalpy and known composition mixture by an iterative method. However, I couldn't locate such a function for psi_ calculation. The only thing I could think of was the equation of state for perfect gas in perfectGasI.H

inline Foam::scalar Foam::perfectGas::psi(scalar, scalar T) const
 {
     return 1.0/(R()*T);
 }

But I'm not sure, and this in itself raises additional questions. Is this where psi_ is calculated or I'm wrong?!

I appreciate it, if you could answer any of the above three questions. Any clue will be of great value to me.

Thanks in advance...