CFD Online Discussion Forums - varying cp with temperature .

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- - varying cp with temperature . (https://www.cfd-online.com/Forums/openfoam-programming-development/84704-varying-cp-temperature.html)

It means that you are trying to solve for two variables within one equation.

Thanks. That is clear . However a formulation like below ,

Code:

fvScalarMatrix hEqn

    (

        fvm::ddt(rho, h)

      + fvm::div(phi, h)

      - fvm::laplacian(turbulence->alphaEff(), h)

     ==

        DpDt

    );

assumes constant k . How does one program without the constant k assumption ?

Hi BalKrishna

Have you found the solution for this problem. How can some body solve 2 variables here.

Regards
Rohith

Dear sir,
I am getting the error after using Foam::tanh(...)

The error is: call of overloaded ‘tanh(const int&)’ is ambiguous
c[ignCell] =1-Foam::tanh(ignSite.cells()[icelli]);

The code is:

forAll(ign.sites(), i)
{
const ignitionSite& ignSite = ign.sites()[i];

if (ignSite.igniting())
{
forAll(ignSite.cells(), icelli)
{
label ignCell = ignSite.cells()[icelli];

c[ignCell] =1-Foam::tanh(ignSite.cells()[icelli]);
}
}
}

Hi Sandip,

I hope tanh in openfoam takes only a value i.e if you define a dimensionedScalar then please define its value. See that there exists no Fields. I See Ignsites is a constant, i am not sure. If you can define it so.

Best Regards,
Rohith

Thanks Raghavendra

I have tried with the interger value 5,
but still i am getting the same error:

call of overloaded ‘tanh(int)’ is ambiguous
c[ignCell] =Foam::tanh(5);

Hello friends,
I am compile the below mention code and i am getting the error

error: ‘distance’ was not declared in this scope
c = Foam::tanh[distance];

Code:

 

pointField meshPoints(mesh.points());

       label i(0);

       

       forAll( meshPoints, kk)

       {   

        vector curPoint = meshPoints[kk];

        vector distance = curPoint - vector(0, 0, 0);

     

        i++;

    scalar dis = mag(distance);    

        Info<< "distance = " << dis << endl;

  

      }

      Info << i << "  Points are changed" << endl;

       

    volScalarField  c = Foam::tanh[distance];

Quote:

Originally Posted by balkrishna (Post 296408)

When i rewrite the enthalpy equation as :

Code:

fvScalarMatrix hEqn

          (

           fvm::ddt(rho, h)

           + fvm::div(phi, h)

           ==

            fvm::laplacian(k,T)

           + DpDt + heatSource

           );

//In the above , k is thermal conductivity , T is temperature , h is enthalpy .

I get the following error :

Code:

incompatible fields for operation 

    [h] == [T]



    From function checkMethod(const fvMatrix<Type>&, const fvMatrix<Type>&)

    in file /home/ifmg/OpenFOAM/OpenFOAM-1.7.0/src/finiteVolume/lnInclude/fvMatrix.C at line 1181.

How to overcome it ?

Hi i knw this post is old but i need help on this problem :D
in my case Cp varies in different locations, so I need to write energy equation with enthalpy. I wrote it like this:

Code:

   fvScalarMatrix EEqn

    (

        fvm::div(phi, E)

      - fvm::laplacian(k_n/cp, E)

     ==

        fvOptions(rho,E)

    );



    EEqn.relax();



    fvOptions.constrain(EEqn);



    EEqn.solve();



    fvOptions.correct(E);

    T=E/cp;

    rhok = (1.0 - beta*(T - TRef));

but I got unrealistic solution that diverges!
can u help me?:confused:

Hi,

The only error i see is that you have defined enthalpy as E=cp*T But it is
deltaE = cp*deltaT.

Hope it helps

Regards,
Rohith

Quote:

Originally Posted by RaghavendraRohith (Post 607515)

Hi,

The only error i see is that you have defined enthalpy as E=cp*T But it is
deltaE = cp*deltaT.

Hope it helps

Regards,
Rohith

HI!
thank u for ur response:) but I didnt get it!:confused: if we replace E with cp*T in

Code:

    (

        fvm::div(phi, E)

      - fvm::laplacian(k_n/cp, E)

     ==

        fvOptions(rho,E)

    );

the result would be like:

Code:

    (

        fvm::div(phiCp, T)

      - fvm::laplacian(k_n, T)

     ==

        fvOptions(rhoCp,T)

    );

so isnt EEqn correct?

actually first I tried TEqn like this:

Code:

    (

        fvm::div(phiCp, T)

      - fvm::laplacian(k_n, T)

     ==

        fvOptions(rhoCp,T)

    );

but I didnt get correct results!
but when I assume that cp is constant! like this:

Code:

    (

        cp*fvm::div(phi, T)

      - fvm::laplacian(k_n, T)

     ==

        fvOptions(rhoCp,T)

    );

I get good results! although the variation of cp is not very significant!
so I tried EEqn :D