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snippet for a custom variable which is a product of two variables

Dear Fellows

In my solver, by solving transport equations, I am achieving $\rho_e$ which is bulk charge density and

which is velocity. I have added the following snippet in my createFields.H file:

I want to find the distribution of $\rho_e * U_x$ from my code in which

is the component of velocity in x direction.

I have added the following snippet in my createFields.H file:

Code:

 volScalarField Ux

        (

            IOobject

            (

                "Ux",

                runTime.timeName(),

                mesh,

                IOobject::NO_READ,

                IOobject::NO_WRITE

            ),

            U.component(vector::X)

        );



volScalarField rhoE      

    (

        IOobject

        (

            "rhoE",

            runTime.timeName(),

            mesh,

            IOobject::READ_IF_PRESENT,

            IOobject::AUTO_WRITE

        ),

        mesh

//    dimensionedScalar("rhoE", dimensionSet(0, -3, 1, 0, 0, 1, 0), scalar(0.0))

    );



  volScalarField rhoEUx

    ( 

     IOobject

        (

            "rhoEUx",

             runTime.timeName(),

             mesh,

             IOobject::NO_READ,

             IOobject::AUTO_WRITE

         ),

         rhoE*Ux

     );

And I have added this line to my Ueqn.H

Code:

     rhoEUx = rhoE * Ux;

    

 //     volVectorField temptemp = rhoE*E;





//    volVectorField temptemp = 3e-06*(fvc::grad(UeExt));

    fvVectorMatrix UEqn

    (

        fvm::ddt(rho, U)

      + fvm::div(rhoPhi, U)

      - fvm::laplacian(muEff, U)

      - (fvc::grad(U) & fvc::grad(muEff))

      - tmp2

      - tmp1 

    );



    UEqn.relax();

Everything with the solver is fine, However, although the values for $\rho_e$ and

are calculated correctly, the $\rho_e * U_x$ is not correct from the code,

However if I use calculator filter in paraview, I would be able to create the distribution of $\rho_e * U_x$ . Does any body know, where did I make mistake?

Regards

You have to update the fields rhoE and Ux in every timestep, because at least for Ux in createFields.H you only do this once at the beginning of the simulation.

So your code should look something like this:

Code:

// rhoE = ???; // not sure what this is. Do you set this somewhere else in your solver?

Ux = U.component(vector::X);

rhoEUx = rhoE * Ux;

Many thanks Joachim

I will test it and give the feedback.
This is my main code:

Code:

while (runTime.run()) 

    { 

        #include "readTimeControls.H" 

        #include "CourantNo.H" 

        #include "alphaCourantNo.H" 

        #include "setDeltaT.H" 

 

        runTime++; 

 

        Info<< "Time = " << runTime.timeName() << nl << endl; 

 

        twoPhaseProperties.correct(); 

 

        #include "alphaEqnSubCycle.H" 

        #include "ElectricEqn.H" 

    #include "SourceTerm.H" 

         //Info<< "ElectricEqn over " << nl << endl; 

        // --- Pressure-velocity PIMPLE corrector loop 

        while (pimple.loop()) 

        { 

         

            #include "UEqn.H" 

 

            // --- Pressure corrector loop 

            while (pimple.correct()) 

            { 

                #include "pEqn.H" 

            } 

 

            if (pimple.turbCorr()) 

            { 

                turbulence->correct(); 

            } 

        } 

 

        runTime.write(); 

 

        Info<< "ExecutionTime = " << runTime.elapsedCpuTime() << " s" 

            << "  ClockTime = " << runTime.elapsedClockTime() << " s" 

            << nl << endl; 

    }

$\rho_e$ is calculated in ElectricEqn.H file, and then I need to multiply it with the

which is the x component of momentum equation.

I updated the Ueqn.H file as:

Code:



    Ux = U.component(vector::X);



       rhoEUx = rhoE * Ux;

    

 //     volVectorField temptemp = rhoE*E;





//    volVectorField temptemp = 3e-06*(fvc::grad(UeExt));

    fvVectorMatrix UEqn

    (

        fvm::ddt(rho, U)

      + fvm::div(rhoPhi, U)

      - fvm::laplacian(muEff, U)

      - (fvc::grad(U) & fvc::grad(muEff))

      - tmp2

      - tmp1 

    );



    UEqn.relax();

Regards

Many Thanks Joachim.

It seems that the update of

at each time step was required, Just by adding the line:

Code:

Ux = U.component(vector::X);

In UEqn.H before everything else, Now everything is fine.:)

Regards

Actually, I think, you don't need the Ux field. You could just use U.component(vector::X) in your calculation of rhoEUx. I would even expect the compiler to optimize it away.

Most likely, u are correct, since

Code:

U.component(vector::X)

is known by OpenFOAM. So I just needed to use that instead of U_x.
By invoking

Code:

U.component(vector::X)

in the formulation:

Code:

rhoEUx = rhoE * U.component(vector::X);

it would be updated automatically, too.

Regards

Hey guys,

Do you know how to create custom variables in postprocessing, ie after the simulation has run? in order to say mucking around with the C and H files?