# psi in compressibleInterFoam (OpenFoam)

 Register Blogs Members List Search Today's Posts Mark Forums Read

 April 4, 2013, 11:36 psi in compressibleInterFoam (OpenFoam) #1 New Member   Clement Olivier Join Date: Mar 2013 Posts: 7 Rep Power: 13 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 New Member   Aaron Join Date: Mar 2013 Posts: 10 Rep Power: 13 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 Member   Rohith Join Date: Oct 2012 Location: Germany Posts: 57 Rep Power: 13 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 Z.Q. Niu, musabai and HenriW like this.

 February 9, 2016, 06:52 totalPressure definition #4 New Member   Join Date: Feb 2016 Posts: 13 Rep Power: 10 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 Member   Rohith Join Date: Oct 2012 Location: Germany Posts: 57 Rep Power: 13 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 New Member   Join Date: Apr 2016 Posts: 4 Rep Power: 10 Hi, everyone, If it still can help anybody, in studying the Programmer's Guide OF v. 3.0.1, I,ve found, in section 3.4, the definition of psi (): which is called the barotropic relationship (compressibility), and its unit is s²/m² (at least for sonicLiquidFoam). saltyFish and Weitao like this.

February 8, 2018, 12:31
#7
Member

Alexander
Join Date: Mar 2009
Posts: 49
Rep Power: 17
Quote:
 Originally Posted by acs Hi, everyone, If it still can help anybody, in studying the Programmer's Guide OF v. 3.0.1, I,ve found, in section 3.4, the definition of psi (): which is called the barotropic relationship (compressibility), and its unit is s²/m² (at least for sonicLiquidFoam).
The problem is that this definition of psi is unambiguous.
It can be

in isothermal case, and

in adiabatic case. Can we be sure that psi is determined by the first formula in all cases?

February 9, 2018, 01:32
#8
Member

Maximus Arelius
Join Date: Jan 2017
Location: Morocco
Posts: 36
Rep Power: 9
Quote:
 Originally Posted by sahas The problem is that this definition of psi is unambiguous. It can be in isothermal case, and in adiabatic case. Can we be sure that psi is determined by the first formula in all cases?
I checked the source code for compressibleInterFoam and based on the thermo library used, I can say that psi is surely 1/RT (at least for a perfect fluid). It may vary according to the the equation of state chosen at runtime.
Please correct me if I am wrong!
ES7

 March 21, 2018, 17:39 OpenFOAM docs #9 New Member   Arpit Join Date: Nov 2015 Posts: 3 Rep Power: 10 This might be useful. You can look up different versions (v3 and above). https://cfd.direct/openfoam/user-gui...hermophysical/

 May 11, 2019, 04:33 Add a non-linear equation of state to foam #10 Senior Member   A. Min Join Date: Mar 2015 Posts: 305 Rep Power: 12 Hi foamers, I want to add a non-linear 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 non-linear 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 Senior Member   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, cochran-chan, 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/synthetik-technologies/blastfoam Hope this helps! Peter Vonk Synthetik Applied Technologies

 Tags compressibility, compressibleinterfoam, openfoam, perfectfluid, psi