CFD Online Discussion Forums - how to output a solved parameter of an equation?

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how to output a solved parameter of an equation?

hello everyone,

Let's say i want to write each writeInterval the Nusselt number for every cell (or the average Nu number for the whole domain, even better), which is solved in the heatTransferModels/RanzMarshall/RanzMarshall.C let's say, in the twoPhaseEulerFoam solver.

How does somebody do that?
Thank you

One option is to modify the solver, look in "createFields.H" and add a new volScalarField here for Nu. With the AUTO_WRITE option this will be written when the other fields are written. Then add the code to calculate the Nusselt number at a suitable place in the solver, and recompile the solver. To get the average number you can then use the normal function object functionality to calculate averages.

It's a bit cumbersome, but should teach you a bit about the inner workings of OpenFOAM for further development later :)

thanx for the "espresso" reply!

I 've tried your way, but it did not work. What you are saying may seem to work (it's a guess of mine) in cases like the wall heat flux. I'm modeling heat transfer in solid/gas fluidized beds, where the Nusselt number is between particle and gas.

The particle Nusselt number is calculated inside the twoPhaseEulerFoam's code and is used in the enthalpy equation, i think.
I am giving you the location in the solver:
applications/solvers/multiphase/myTwoPhaseEulerFoam/interfacialModels/heatTransferModels/RanzMarshall/RanzMarshall.C

Code:

Foam::tmp<Foam::volScalarField>

Foam::heatTransferModels::RanzMarshall::K() const

{

    volScalarField Nu(scalar(2) + 0.6*sqrt(pair_.Re())*cbrt(pair_.Pr()));



    return

        6.0

       *max(pair_.dispersed(), residualAlpha_)

       *pair_.continuous().kappa()

       *Nu

       /sqr(pair_.dispersed().d());

}

So i need to extract this "Nu", besides the function does not return it (and the "Re" also).

I have also tried unsuccessfully to extract by modifying my controlDict like that:

Code:

functions {     

name4me     {         

type writeRegisteredObject;         

functionObjectLibs ( "libIOFunctionObjects.so" );         

objectNames ("Nu");         

outputControl outputTime;         

outputInterval       1;     } }

but i can't find why it's not detecting it.

Regards

Code:

Foam::tmp<Foam::volScalarField>

Foam::heatTransferModels::RanzMarshall::K() const

{

    volScalarField Nu(scalar(2) + 0.6*sqrt(pair_.Re())*cbrt(pair_.Pr()));



    return

        6.0

       *max(pair_.dispersed(), residualAlpha_)

       *pair_.continuous().kappa()

       *Nu

       /sqr(pair_.dispersed().d());

}

So i need to extract this "Nu", besides the function does not return it (and the "Re" also).

I have also tried unsuccessfully to extract by modifying my controlDict like that:

Code:



functions

{

    name4me

    {

        type writeRegisteredObject;

        functionObjectLibs ( "libIOFunctionObjects.so" );

        objectNames ("Nu");

        outputControl outputTime;

        outputInterval       1;

    }

}

but i can't find why it's not detecting it.

Regards

I din't know whether you really need each cell. Ususally, I work with sample, which is called afterwards.