[papadeiv]

New to OpenFOAM and therefore I might am trying to make this to work out by force whereas there is a much better way to do it.

Basically I want to solve an advection equation for a passive scalar :



scalarTransportFoam is the ideal solver for that by setting the diffusivity to 0, however it lacks the possibility of setting a space-time dependent mathematical expression for the advection field.

So I modified the solver by computing the volVectorField at each step of the simple loop, specifically

while (simple.loop()){  
         #include "updateTransport.H"
         while (simple.correctNonOrthogonal()){
            fvScalarMatrix TEqn
            (
                      fvm::ddt(T)+fvm::div(phi, T)== fvOptions(T)
            );
            TEqn.relax();
            fvOptions.constrain(TEqn);
            TEqn.solve();
            fvOptions.correct(T);
        }
        runTime.write();
}

where in "updateTransport.H" I perform the operation of updating the surfaceScalarField phi modelling the advection

volVectorField U_update = U;
U_update.rename("U");

for(label l=0; l < mesh.C().size(); l++){
    scalar x = mesh.C()[l][0];
    scalar y = mesh.C()[l][1];
    scalar z = mesh.C()[l][2];
    scalar t = runTime.value();

    U_update[l].x() = t+y;
    U_update[l].y() = x*Foam::cos(t);
    U_update[l].z() = z;
}

surfaceScalarField phi
(
    IOobject
    (
        "phi",
        runTime.timeName(),
        mesh,
        IOobject::READ_IF_PRESENT,
        IOobject::AUTO_WRITE
    ),
    fvc::flux(U_update)
);

Now, the solver works just fine however it is not conveniente since I must recompile it everytime I change the mathematical form for the advection field.

Ideally I would like to write the mathematical expression in the case directory (say for example in the constant/transportProperties file) and let the solver read it via an IOdictionary object to update the volVectorField at each time-step.

I am aware of the existance of expressions however my understanding is that they are used to set IC/BCs in setExprFieldsDict and setFieldsDict and not to be used within the solver itself?

Been searching the web and reading both the user and developer's guide for the last 2 days however nothing comes up that brings me closer to achieve what I just described. Any help/suggestion is greatly appreciated.