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psi in compressibleInterFoam (OpenFoam) 

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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
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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
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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
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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, 06:52 
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, 03:51 

#5 
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Rohith
Join Date: Oct 2012
Location: Germany
Posts: 57
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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, 09:17 
from the Programmer's Guide v 3.0.1

#6 
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February 8, 2018, 12:31 

#7 
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Alexander
Join Date: Mar 2009
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February 9, 2018, 01:32 

#8  
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Maximus Arelius
Join Date: Jan 2017
Location: Morocco
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Quote:
Please correct me if I am wrong! ES7 

March 21, 2018, 17:39 
OpenFOAM docs

#9 
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Arpit
Join Date: Nov 2015
Posts: 3
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This might be useful. You can look up different versions (v3 and above).
https://cfd.direct/openfoam/usergui...hermophysical/ 

May 11, 2019, 04:33 
Add a nonlinear equation of state to foam

#10 
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A. Min
Join Date: Mar 2015
Posts: 305
Rep Power: 12 
Hi foamers,
I want to add a nonlinear equation of state (JWL) to foam to use in sonicFoam. In this equation, I need to calculate rho, Cp, h, s, psi, Z, and cpMcv and some functions such as: correct (which is used in EEqn.H: thermo.correct() ) pThermo(which is used in createFields.H: thermo.pThermo() ) p (which is used in createFields.H: thermo.p() ) rho (which is used in createFields.H: thermo.rho() ) he (which is used in createFieldRefs.H: thermo.he() ) psi (which is used in createFieldRefs.H: thermo.psi() ) But JWL is nonlinear and calculation of parameters are not as easy as perfectGas! However, I have calculated rho using Newton method in rho() function. But I don't know how to calculate the others! Thanks 

May 12, 2019, 09:37 

#11 
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A. Min
Join Date: Mar 2015
Posts: 305
Rep Power: 12 
Dear foamers,
my last problem is not solved yet! In addition I want to know: 1 How can I calculate "h", "Cp" for my new equation of state? why Cp and h are zero for perfectGas model in openFoam? and how did they calculate "s=R*log(p/Pstd)" ? Thanks 

October 30, 2019, 11:32 
JWL implementation that works with OpenFOAM

#12 
Member
Peter
Join Date: Feb 2015
Location: New York
Posts: 73
Rep Power: 11 
Hi,
Yes, we have just released a new solver (blastFoam) which includes the JWL equation of state (an extensions to model afterburn), as well as several other useful and interoperable equations of state (e.g. ideal gas, stiffened gas, tait, cochranchan, van der waals, JWL), flux schemes (HLLC, AUSM+, Kurganov/Tadmor), and multiple examples/tutorial cases. Source, user guide and examples are available here: https://github.com/synthetiktechnologies/blastfoam Hope this helps! Peter Vonk Synthetik Applied Technologies 

Tags 
compressibility, compressibleinterfoam, openfoam, perfectfluid, psi 
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