[Nek5000-users] convective boundary conditions

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

Hi Goran,

thank you for your answer. However I still not understand very well what 
happens in your simulation if you are using unphysical boundary 
conditions... Activating turb_outflow subroutine, are you emulating a 
suction (from the boundary to the inner domain)? In this case, is it not 
affecting your physical results from your numerical simulation? Please, 
correct me if I am wrong...

One more question, the effect that you are producing with the 
turb_outflow subroutine, is it similar to applying convective boundary 
condition?

Thanks again.
SL



El 10-03-2016 04:27, nek5000-users at lists.mcs.anl.gov escribió:
> 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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