[Nek5000-users] convective boundary conditions

[nek5000-users at lists.mcs.anl.gov]

Hi Neks,

regarding my question about convective boundary conditions:

In the problem that I am solving, there are vortex traveling across the 
boundary. Using O boundary conditions, the solution blows up (due to the 
negative flux of the vortex). On the contrary, if I use ON, the 
simulation continues running, but I get very strong reflections.

In addition, although my flow is laminar, if I use turb_outflow 
subroutine (with O boundary conditions) with rq=2, the simulation works 
better, but at a certain moment, it also crashes. I am wondering if I 
should increase rq to, let say 3, or maybe I should use a different 
boundary condition, i.e. non reflective.

I would like to ask, if I am using turb_outflow subroutine I am imposing 
grad U>0 in the boundary (please correct me if I am wrong). The question 
is, is it physical? What I am doing is
-pn+(1/Re)(n*grad(U))>0 ? What does it mean?

Finally, I have seen that in 2015 you implemented some non-reflective 
boundary conditions and they were working very well. Please, could you 
help me with this issue? (i.e.: a piece of advise or some procedure to 
follow...)

Thank you very much in advance.
SL