[ALBATTROSS]

Hello all,


I'm working on problem in which knowing the magnitude of shear rate tensor is important to me. I added these lines to createFields.H file in solver's folder (buoyantBoussinesqPimpleFoam) and recompiled it in order to have the shear rate magnitude in each time step:

volScalarField shearRate
    (
    IOobject 
        (
            "shearRate",
            runTime.timeName(),
            mesh,
            IOobject::NO_READ,
            IOobject::AUTO_WRITE
        ),
        sqrt(2.0f)*mag(symm(fvc::grad(U)))
    );

I used the expression of the shear rate magnitude from the viscosityModel.C in src. and it works I have a file of shear rate in each written time step. the problem is that the output magnitude all over the internal field is zero in every time step and this is wrong, I'm sure about the validity of my results for other parameters though.
is anything wrong with this expression:
shearRate=sqrt(2.0f)*mag(symm(fvc::grad(U)))


or it's a programming problem?


Thank you is advance!
Amir

[giano]

I have the same problem, but so far I did not manage to solve it.

[Kellis]

Amir,

The createFields.H file is only called once, at the beginning of the simulation. Assuming you are starting with a zero or otherwise uniform velocity field, the shear rate will be zero. If you are not updating the shear rate somewhere else in the code, the shear rate will be initialized in createFields and then never updated as the simulation progresses.

To fix this, simply add another line of code (perhaps at the end of pEqn.H, once the velocity field for the timestep is finalized) to recalculate the shear rate with the updated velocity field. Then you should be seeing non-zero values as your case progresses.

Hope this helps.

Kellis