My question is mainly about whether the tutorial is actually using an outflow condition:
-p \cdot n + \nabla u \cdot n = 0
Because if we were, wouldn’t these terms just be ignored when writing the linear variational formulation:
F1 = rho*dot((u - u_n) / k, v)*dx \
+ rho*dot(dot(u_n, nabla_grad(u_n)), v)*dx \
+ inner(sigma(U, p_n), epsilon(v))*dx \
+ dot(p_n*n, v)*ds - dot(mu*nabla_grad(U)*n, v)*ds \ This line!!!
- dot(f, v)*dx
Why does we instead prescribe a Dirichlet pressure boundary condition:
bcp_outflow = DirichletBC(Q, Constant(0), boundaries, outlet_tag)
Why do we include these terms if it is really an outflow condition? Is it like using the Dirichlet pressure condition to set p=0 to make pn = 0 and then somehow make the other term also zero (someone answered a question like that but it did not make sense to me (Pressure should be a Neumann BC?)
Can someone clarify this?
That is, if it is what the tutorial is doing. If what I’m saying make no sense please educate me.
Thanks in advance.