Surface Traction term for Navier Stokes

[Nikhil Vaidya]

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

[Robert Cimrman]

So viscosity * grad(velocity) is known, right? You can use dw_surface_ltr with
the traction vector f = viscosity * grad(velocity) as the material parameter.

r.

> Best regards,
> Nikhil
>

[Nikhil Vaidya]

OK. It is still not completely clear to me. Should I define a user function and then pass it to the terms in the equation?

Best regards,
Nikhil

[Robert Cimrman]

It depends if the given velocity is constant or not. If it is not constant, you
need to define the material parameter using a function [1, 2].

r.

[1] http://sfepy.org/doc-devel/users_guide.html#defining-material-parameters
[2]
http://sfepy.org/doc-devel/examples/linear_elasticity/linear_elastic_tractions.html