CFD Online Discussion Forums - BC development: how can I access to the patch normal?

Dear Foamer,

I'm currently developing a boundary condition to force a given pressure gradient.

For a gradient boundary condition, OpenFOAM needs the normal gradient, for example, a fixed pressure gradient looks like this (in the p file):

Code:

outlet

    {

        type            fixedValue;

        value           uniform 1;

       //value         uniform (1 0 0); <== this is wrong!

    }

In my new bc, I'm working with the pressure gradient, which is a vector. but at the very end of all my calculations, I need to do the dot product between the pressure gradient and the patch normal, which should lead to something like this:

Code:

Field<scalar>& gradient = this->gradient();

gradient = myGradP*patchNormal  //how to get "patchNormal"?

In this example, "myGradP" is a vectorField with the same size as "gradient".

The problem, I don't now how to access to the patch normal. Any Idea?

Cheers,
Marcel