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error : invalid use of void expression

hi foamers.

my problem is entrophy Generation shown in following picture :

http://www.cfd-online.com/Forums/att...n-untitled.png
i write a code for of220 & got this error.
code:

Code:

    volVectorField gradT = fvc::grad(T);    

        volScalarField gradTx = gradT.component(0);

        volScalarField gradTy = gradT.component(1);

        

    volScalarField uX = U.component(0);

    volScalarField uY = U.component(1);

    volVectorField graduX = fvc::grad(uX);

    volVectorField graduY = fvc::grad(uY);

        volScalarField dudx = graduX.component(0);

        volScalarField dvdy = graduY.component(1);

        volScalarField dudy = graduX.component(1);

        volScalarField dvdx = graduY.component(0);

   



fvScalarMatrix SEqn

(

          Sgen

        == (k/Foam::pow(T,2))*(Foam::pow(gradTx,2)+Foam::pow(gradTy,2))

         + (mu/T)*(Foam::pow(dudx,2)+Foam::pow(dvdy,2))*2

         + (mu/T)*Foam::pow((dudy+dvdx),2)

); 



SEqn.solve();

error:

Code:

In file included from myPorousSimpleFoam.C:73:0:

SEqn.H: In function ‘int main(int, char**)’:

SEqn.H:21:1: error: invalid use of void expression

make: *** [Make/linux64GccDPOpt/myPorousSimpleFoam.o] Error 1

Which line is number 21?

Quote:

Originally Posted by akidess (Post 453850)

Which line is number 21?

thanks anton. my problem is solved.

using fvc::grad is an explicit operation that actually returns an volScalarFields, not fvScalarMatrix.

Code:

volScalarField Sgen

(

           (k/Foam::pow(T,2))*(Foam::pow(gradTx,2)+Foam::pow(gradTy,2))

         + (mu/T)*(Foam::pow(dudx,2)+Foam::pow(dvdy,2))*2

         + (mu/T)*Foam::pow((dudy+dvdx),2)

);