Problem with definition of normal gradient to a surface
 

Hi guys!

I'm experiencing some troubles with the definition of the normal gradient of the velocity to a patch. What I need to obtain is the normal gradient to the patch of the normal component of the velocity and the tangential component of the velocity separately.

So I've tried so implement this piece of code:

word patchName1 = "foil";
label patchID1 = mesh.boundary().findPatchID(patchName1);
vectorField UN((mesh.boundary()[patchID1].nf() & U.boundaryField()[patchID1]) * mesh.boundary()[patchID1].nf());
vectorField UT(U.boundaryField()[patchID1] - UN);
vectorField gradUT(fvc::snGrad(UT));

But it doesn't work. Do you have any ideas? I really don't know what to do.

Cheers
Simone

There isn't anyone who can give me a suggestion?