[Nek5000-users] SYM boundary conditions

Wed Feb 10 16:46:11 CST 2016

The flow is turbulent in the real case. It is also an external flow...

About damping the turbulence using a forcing, do you mean that I could 
add something like ffx=-sin(omega*time) in the userf subroutine (being 
ux=sin(omega*time))? Or do you mean that I should use a selective 
frequency damping subroutine?

About turn_outflow() routine, it is working when the flow is external?

Does it make sense using SYM in the sides of the domain and ON in the 
outlet surface? Or the idea is using ON in both, the sides and the 
outlet surface?

Thank you very much for your help.
Cheers
SL

El 10-02-2016 15:36, nek5000-users at lists.mcs.anl.gov escribió:
> Is this an internal flow, or external flow?
> 
> If internal, you can use the turn_outflow() routine with sufficient
> divergence to ensure
> that the flow is always leaving the domain.  We use this for some of
> our moving domain
> simulations.
> 
> Paul
> 
> ________________________________________
> From: nek5000-users-bounces at lists.mcs.anl.gov
> [nek5000-users-bounces at lists.mcs.anl.gov] on behalf of
> nek5000-users at lists.mcs.anl.gov [nek5000-users at lists.mcs.anl.gov]
> Sent: Wednesday, February 10, 2016 8:04 AM
> To: nek5000-users at lists.mcs.anl.gov
> Subject: Re: [Nek5000-users] SYM boundary conditions
> 
> ok, I see. If it is turbulent, then it is a bit more difficult. You can
> try ON, but perhaps it will not work. But in the real case, what type 
> of
> inflow are you going to have, something turbulent? What about damping
> the turbulence before it actually reaches the outflow boundary, e.g.
> using a forcing? ONce it is laminar, I think that ON could work.
> 
> Philipp
> 
> On 2016-02-10 13:02, nek5000-users at lists.mcs.anl.gov wrote:
>> Yes, it is turbulent...
>> 
>> I will try to use ON. Please, could you help me to understand a bit 
>> more
>> why it could work?
>> 
>> Thanks again!
>> Cheers
>> SL
>> 
>> 
>> El 10-02-2016 12:17, nek5000-users at lists.mcs.anl.gov escribió:
>>> one initial suggestion would be to use ON at the outflow. Is the flow
>>> turbulent at the outflow boundary?
>>> Philipp
>>> 
>>> On 2016-02-10 11:45, nek5000-users at lists.mcs.anl.gov wrote:
>>>> Hi,
>>>> 
>>>> Thank you. I am trying to simulate a flow whose inlet boundary 
>>>> condition
>>>> is time periodic ux=sin(omega*time). Since there is an injection and 
>>>> a
>>>> suction, and the mean flow is zero, I think that the boundary 
>>>> conditions
>>>> should let the transpiration/penetration of the flow... (I have 
>>>> tried to
>>>> run the simulation using outflow BC but it crashes). Is there any BC
>>>> condition in Nek5000 that suits to this problem?
>>>> 
>>>> Thank you for your help in advance.
>>>> Best regards,
>>>> SL
>>>> 
>>>> El 10-02-2016 10:20, nek5000-users at lists.mcs.anl.gov escribió:
>>>>> Hi,
>>>>> SYM is essentially means that the velocity through the interface is
>>>>> zero and for the inplane velocities that the normal gradients 
>>>>> vanish.
>>>>> So it does not allow transpiration/penetration through the 
>>>>> boundary.
>>>>> So I suspect that this condition is not what you are looking for.
>>>>> 
>>>>> However, I am not exactly sure what you really mean. Perhaps you 
>>>>> can
>>>>> say a bit more about your case?
>>>>> 
>>>>> Best regards,
>>>>> Philipp
>>>>> 
>>>>> On 2016-02-10 08:02, nek5000-users at lists.mcs.anl.gov wrote:
>>>>>> Hi Neks,
>>>>>> 
>>>>>> I am looking for a boundary condition that leads the flow to go 
>>>>>> out or
>>>>>> to go into the domain.
>>>>>> 
>>>>>> Is 'SYM' valid for this purpose?
>>>>>> 
>>>>>> 
>>>>>> I think that what I am looking for is, in the outlet surface:
>>>>>> 
>>>>>>    - If the velocity vector at the outlet points out of the 
>>>>>> domain,
>>>>>> then
>>>>>> the boundary condition for the velocity will be of the Neumann 
>>>>>> type
>>>>>> 
>>>>>>    - However, if the velocity at the outlet points into the 
>>>>>> domain,
>>>>>> then
>>>>>> we can imagine that the outflow is no longer an outflow, but an
>>>>>> inflow,
>>>>>> and that we therefore would like to specify a Dirichlet boundary
>>>>>> condition for velocity
>>>>>> 
>>>>>> 
>>>>>> Thanks in advance
>>>>>> SL
>>>>>> 
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