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- - **psi in compressibleInterFoam (OpenFoam)**
(*https://www.cfd-online.com/Forums/openfoam-solving/115674-psi-compressibleinterfoam-openfoam.html*)

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 ... Edit: Continuing with the dimensional line of thought, so the units work out in that regard. Regards, Aaron |

Hi
I think the compressibility is actually the reverse that is being defined above. It is psi = rho/p which makes it a isothermal compressibility Thanks RR |

totalPressure definitionHi,
In totalPressureFvPatchScalarField.H we can read that for compressible supersonic flow the total pressure is defined as : \f[ p_p = \frac{p_0}{(1 + 0.5 \psi G |U|^2)^{\frac{1}{G}}} \f] where \vartable p_p | pressure at patch [Pa] p_0 | total pressure [Pa] \gamma | ratio of specific heats (Cp/Cv) \psi | compressibility [m2/s2] G | coefficient given by \f$\frac{\gamma}{1-\gamma}\f$ \endvartable What compressibility is ? is its dimension really m2/s2 ? and really not s2/m2 ??. I would expect s2/m2 in order to obtain psi*U^2 as an unidimensional number .. I am also surprised by the G definition. It is really \frac{\gamma}{1-\gamma} ? I would expect the inverse frac{1-\gamma}{\gamma} ? Does someone has an opinion on it? Regards Fanny |

Hi
I see it is s2/m2 because in the above equation it is multiplied by U2 to get a scalar value. Best Regards, RRK |

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