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April 4, 2013, 11:36 
psi in compressibleInterFoam (OpenFoam)

#1 
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Clement Olivier
Join Date: Mar 2013
Posts: 7
Rep Power: 6 
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 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 Clément 

May 28, 2013, 06:44 

#2 
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Aaron
Join Date: Mar 2013
Posts: 10
Rep Power: 6 
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 Last edited by dalaron; May 28, 2013 at 06:57. Reason: Forgot to add something 

April 24, 2014, 09:08 

#3 
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Rohith
Join Date: Oct 2012
Location: Germany
Posts: 57
Rep Power: 7 
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 

February 9, 2016, 07:52 
totalPressure definition

#4 
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Join Date: Feb 2016
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Hi,
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 

February 12, 2016, 04:51 

#5 
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Rohith
Join Date: Oct 2012
Location: Germany
Posts: 57
Rep Power: 7 
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 

November 21, 2016, 10:17 
from the Programmer's Guide v 3.0.1

#6 
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Join Date: Apr 2016
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Tags 
compressibility, compressibleinterfoam, openfoam, perfectfluid, psi 
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