[lukeweaver]

I'm trying to use an arbitrary "box" to calculate the flux around an actuator disc (reduced-order wind turbine model). However, the calculation for massflow over each surface is not being conserved.

The domain is a rectangular box with axial flow over a plane. The solver is simpleFoam.

The interior box is 80 x 160 x 160 m, and the surfaces are selected using the topoSet with slave cells and faceset as follows:

{
        name    north1SlaveCells;
        type    cellSet;
        action  new;
        source expressionToCell;
        sourceInfo
        {
            expression "(pos().x<=60 && pos().y>=20 && pos().y<=180 && pos().z>=20 && pos().z<=180)";
        }
}
{
        name    north1;
        type    faceSet;
        action  new;
        source  expressionToFace;
        sourceInfo
        {
            expression "(pos().x<=60 && pos().y>=20 && pos().y<=180 && pos().z>=20 && pos().z<=180)";
        }
}

This is done for all six sides (top, bottom,south,east,west). Here's three of the faceSets shown in paraView.

faceSet.jpg

Imagine the box fitting inside these three with the other three faceSets filling in the open space.

In the controlDict, I calculate the massflow:

PhiNorth1
        {
                type swakExpression;
                valueType faceSet;
                variables "direction=vector(0,1,0);dir=direction/mag(direction);";
                setName north1;
                //expression "U & Sf()";
                //expression "phi * flip()";
                expression "(U & direction) * area()";
                autoInterpolate true;
                accumulations (
                        sum
                        min //just for reference
                        max //just for reference
                );
                outputControlMode timeStep;
                outputInterval 10;
                verbose true;
        }

I used the swak tutorial angledDuctImplicitTransient files to build my topoSetDict and controlDict files.

I calculated the mass flow on each faceSet, and summing them should give Phi_In - Phi_Out = 0. After summing up the phi values on all faceSets, the values were Phi_In = 203,860 and sumPhi_Out 206,270, for a total difference of -2410.7 kg/s.

Any help/tips/explanations for this error?

EDIT: For the upstream and downstream faces, I use the U & Sf(). The phi*flip() condition didn't seem to work.