[TeddyL]

Hi, everyone!

I'm trying to update the boundary condition as the mesh moves using #codeStream, here is a more detailed description for my problem:

I managed to make my own outlet poiseuille flow boundary condition, which gives a parabolic velocity distribution using #codeStream, the codes are like this in 0/U:

outlet
    {
        type                fixedValue;
        value               #codeStream
        {
            codeInclude
            #{
                #include "fvCFD.H"
            #};

            codeOptions
            #{
                -I$(LIB_SRC)/finiteVolume/lnInclude \
                -I$(LIB_SRC)/meshTools/lnInclude
            #};

            codeLibs
            #{
                -lmeshTools \
                -lfiniteVolume
            #};

            code
            #{
                const IOdictionary& d = static_cast<const IOdictionary&>
                (
                    dict.parent().parent()
                );
                const fvMesh& mesh = refCast<const fvMesh>(d.db());
                label id = mesh.boundary().findPatchID("outlet");
                if (id ==-1)
                {
                    FatalError << "patch not found!" << exit(FatalError);
                }

                const fvPatch& patch = refCast<const fvPatch>(mesh.boundary()[id]);

                vectorField NF(patch.nf());

                vectorField U(NF); 

                const scalar pi = constant::mathematical::pi;

                const vector patch_Center = vector(1,0.25,0);
                const scalar patch_R = 0.1;

                const scalar flow_Flux = 0.1; 
                const scalar U_max = 2 * flow_Flux / (pi * pow(patch_R,4));

                forAll(U, i)
                {
                    const scalar x = patch.Cf()[i][0];
                    const scalar y = patch.Cf()[i][1];
                    U[i] = (U_max*(pow(patch_R,2)-pow(x-patch_Center[0],2)-pow(y-patch_Center[1],2)))*NF[i];
                }

                const scalarField area = patch.magSf();
                vectorField pointed_area = patch.Sf();
                scalar areaTotal = gSum(area);
                scalar realize_Flux = mag(gSum((U & pointed_area)()));

                vectorField U_fix(U);
                forAll(U_fix, i)
                {
                    U_fix[i] = U_fix[i] - ((flow_Flux - realize_Flux)/areaTotal)*NF[i];
                }
                
                U_fix.writeEntry("", os);
            #};
        };
    }

I did a kind of fixing to the velocity to make sure the flow flux is consistent with the intended one, i.e. 0.1. It worked well in steady cases where the mesh does't move, and gives a parabolic velocity at the outlet patch that is normal to the patch surface.

The problem occurred when I tried to set the whole mesh to an oscillatingRotatingMotion centered at the outlet patch center. I monitored the outlet flow from the outlet patch, and it gave a sinusoidal curve in a period:

flux.png

which means that the velocity at the patch is no longer normal to the patch face. I checked it in paraView, and it obviously is not normal to the patch according to a closer look around the outlet patch:

detail.png

So the problem here is:

How can I set this boundary condition to get a parabolic velocity field at the patch that is always normal to the patch face? I firstly wanted to realize it with #codeStream, or do I have to use high-level programming? Because I noticed there is a function called "updateCoeffs()" I wondered if it has anything to do with my problem.

This is my first thread here, and sorry for this long story. And any suggestions will be appreciated!

Regards,
Teddy