[Nek5000-users] convective boundary conditions

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

SL,

I had the same problem before. I've had to set rq = 200. If your flow is very turbulent, just turn up that value a lot.

No, it's not physical because you're imposing a divergence on the last layer of elements. You can just exclude that part of your solution in your post processing. 

Regards,

Goran


> On Mar 9, 2016, at 21:58, "nek5000-users at lists.mcs.anl.gov" <nek5000-users at lists.mcs.anl.gov> wrote:
> 
> 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
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