[Lighto]

Hello everyone.

I'm very new to CFD enviroment and OpenFOAM software. I've managed to implement a lagrangian particle tracker inside pimpleFoam (I don't know if I can post here the reference pdf). Now I need to create an output file just like the one for velocity, pressure etc. but for the shear stress on particles, i.e. I need to output first order derivatives of u1,u2,u3 in x1,x2,x3, and then calculate the scalar stress:



where

This last part I think is easier once I understood how to output the spatial derivatives of the particles' velocities.
How can I implement this in OpenFOAM and in which file of the solver?

Thanks for your help.

Davide

[Lighto]

I've read so many topics in these 24 hours but I didn't managed to solve my problem

However I have done a small progress, that I post here.
In the createFields.H file in the solver folder I've added the following lines to output the gradient of the vector field U (named DUDX):

volTensorField DUDX
(
    IOobject
    (
        "DUDX",
        runTime.timeName(),
        mesh,
        IOobject::NO_READ,
        IOobject::AUTO_WRITE
    ),
    mesh,
    //assign dim of tensor and inizialize it to zero
    dimensionedTensor("DUDX", dimVelocity/dimLength, tensor::zero)
);

and update it at every time step in the solver.C file, after the velocity corrector loop:

while (runTime.run())
    {
        ...
        // --- Pressure-velocity PIMPLE corrector loop
        ...
        DUDX = fvc::grad(U);
        ...
    }

(Note: i'm using a pimple solver with lagrangian particle tracking.)

This should output the gradient of the velocity as a tensor of 9 components du1/dx1, du2/dx1, etc. in the whole domain, but I want it only for the particles (so gradient of U of the particles, not U of the fluid).