CFD Online Discussion Forums - How to define multiple ranges for JANAF coefficients? (OF5/OF6)

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How to define multiple ranges for JANAF coefficients? (OF5/OF6)

Hello,

I am accessing the CEA database of NASA for JANAF coefficients beyond the typical range of 200-6000 K. CEA data is expressed in 3 different ranges 200-1000, 1000-6000, 6000-20000 (see attached image for H2).

How do I incorporate three ranges in thermodynamics subdictionary? Is there any way? If not is there any alternative?

Does something like this work?

Code:

thermodynamics

    {

        Tlow1            200; 

        Thigh1           1000;

        Tcommon         1000;

        highCpCoeffs    ( 2.5000 0.0000000 0.00000 0.0000 0.0000 -745.37 4.37 );

        lowCpCoeffs     ( 2.5000 0.0000000 0.00000 0.0000 0.0000 -745.37 4.37 );





        Tlow2            1000;

        Thigh2           6000;

        Tcommon         1000;

        highCpCoeffs    ( 2.5000 0.0000000 0.00000 0.0000 0.0000 -745.37 4.37 );

        lowCpCoeffs     ( 2.5000 0.0000000 0.00000 0.0000 0.0000 -745.37 4.37 );





        Tlow3            6000;

        Thigh3           20000;

        Tcommon         1000;

        highCpCoeffs    ( 2.5000 0.0000000 0.00000 0.0000 0.0000 -745.37 4.37 );

        lowCpCoeffs     ( 2.5000 0.0000000 0.00000 0.0000 0.0000 -745.37 4.37 );

    }

hey deepbandivadekar,
Bad news first: I quickly checked the OFv6 implementation of the Janaf polynomials (https://cpp.openfoam.org/v6/janafThermo_8H_source.html) and it doesn't seem compatible.
Now the good news: It shouldn't be too complicated to implement this functionality in an extra class (ThreeRangeJanafThermo - this is the one you need to implement, basically like janafThermo but with some more if-statements and of course one coeffArray more for the mid range). This class and the mandatory myPsiThermos.C-file* (including your new class into the makeThermo-macros) should be compiled into a new library, which can then be linked to your application through your controlDict. I know it is quite vague (I'm super tired) but I think you can make it work by searching a bit through the forums and digging into the code. I wish you good luck!

Cheers
RP

*myPsiThermos.C or myRhoThermos.C, refering to the type of thermodynamics used in your application.

Quote:

Originally Posted by raumpolizei (Post 721942)

Ok, this gives me some hints.
So it'd rather be like this:

Code:

thermodynamics

    {

        Tlow                   200;

        Tcommon1          1000;

        Tcommon2          6000;

        Thigh                  20000;



         highCpCoeffs    ( Coefficients corresponding to 6000 to 20000 );

        midCpCoeffs    ( Coefficients corresponding to 1000 to 6000 );

        lowCpCoeffs     ( Coefficients corresponding to 200 to 1000 );

 }

Right? I'll read more and update if I have more questions/updates.
Thanks!

Yes, something like this is a good starting point, even though the final version will depend on how you implement it.