Surface Traction term for Navier Stokes

Hello,

I need to use a surface traction term, because I want to apply a pressure dirichlet boundary condition at the inlet for channel flow. In the SfePy term overview page, I can see the term dw_surface_ltr. In my weak form for the Navier Stokes equations, I will need two such terms. One for the stress tensor and one for the pressure. I got the pressure term using the dw_surface_ndot term. I do not understand how to represent the viscosity*vel_test_func.grad(velocity).n term.

Best regards, Nikhil