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clementolivier April 4, 2013 11:36

psi in compressibleInterFoam (OpenFoam)
Hi everyone,

I am currently using the solver compressibleInterFoam (of OpenFoam). I am trying to change the equation of state perfectFluid and therefore, I need to understand what is psi. It seems to be the compressibility defined by
\psi = \left( \frac{\partial \rho}{\partial p} \right)_T
But I am not sure at all.
Moreover, I do not understand the file pEqn.H, and thus it do not help me to understand how psi is used.

If someone could give me some help, I would be very thankful

Best regards


dalaron May 28, 2013 06:44

Hi Clement,

Have you managed to figure this out? I am also looking to implement an equation of state and am not sure what to make of the psi term.

Referring to the documentation for totalPressure boundary condition (which is more in line with my own interests), psi is defined as compressibility and has units m^2/s^2. Beyond that though, I have not seen any documentation about what it actually is ...

Continuing with the dimensional line of thought,
\psi = \frac{P}{\rho} = \frac{kg/ms^2}{kg/m^2}=\frac{m^2}{s^2}
so the units work out in that regard.


RaghavendraRohith April 24, 2014 09:08


I think the compressibility is actually the reverse that is being defined above. It is

psi = rho/p which makes it a isothermal compressibility


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