[Nek5000-users] Pipe example - Strange velocity/pressure signals

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

Hi Outi,

This looks ok to me... I see in your userbc file:

       xp  = x/0.5
       yp  = y/0.5
       rr  = xp*xp + yp*yp

       ux  = 0.0
       uy  = 0.0
       uz  = 1 - rr   ! Hagen-Poiseiulle flow, pipe diamter = 1.

which would give a nonzero velocity after Step 1 ?

Best, Paul






On Sun, 2 Mar 2014, nek5000-users at lists.mcs.anl.gov wrote:

> Dear Paul,
>
> Thank you very much for looking into this. My parameters are as in the repository example, I didn't change them:
> lx1=6,
> lxd=10,
> lx2=lx1-2
> lx3=lx1
>
> The output after the first time step (dt=2.5e-2) of hpts.out is attached below. Please note the third column (z-velocity).
>
>  2.5000000E-02 -4.7626817E-05 -4.4872405E-05  4.8233404E-01  1.3486090E+02
>  2.5000000E-02 -6.0842050E-05 -1.8870027E-02  5.9476094E-01  1.7381205E+02
>  2.5000000E-02  2.0295515E-07 -1.5249089E-02  4.8242873E-01  1.3487912E+02
>  2.5000000E-02 -1.5349154E-02 -1.1545977E-05  4.8241771E-01  1.3487899E+02
>  2.5000000E-02  9.8682769E-03 -1.7779070E-02  5.7201214E-01  1.7367640E+02
>
> Best regards,
> Outi
>
>
>
> On Mar 2, 2014, at 9:02 PM, nek5000-users at lists.mcs.anl.gov wrote:
>
>>
>> Dear Outi,
>>
>> What value of lx1 and lx2 were you using?
>>
>> I'm not observing the phenomenon you report.
>> I have:
>>
>> lx1=6
>> lxd=9
>> lx2=lx1-2
>> lx3=lx2
>>
>> ...
>>
>> Once I know your SIZE parameters I can retry.
>>
>> Best, Paul
>>
>>
>> On Sun, 2 Mar 2014, nek5000-users at lists.mcs.anl.gov wrote:
>>
>>> Dear Neks,
>>> We are interested to do a smoothly deformed axisymmetric geometry, much
>>> like the pipe/stenosis example in the repository.
>>> So, we added hpts probes in the pipe example, and modified nothing else,
>>> but this turns out to give strange values initially. The first probe sits
>>> 3 diameters downstream of the stenosis throat (z=3), and gives U=0.48 at
>>> the first time step, despite zero initial condition. The pressure in this
>>> position shoots up to very high values too, so maybe a spurious pressure
>>> peak is the cause?
>>> Could you please help us to understand/prevent this phenomenon? The .usr,
>>> hpts.in and essential parts of .rea are attached. We are using revision
>>> 1008.
>>> This would be important for us as we aim to use Nek5000 to study
>>> transient as well as steady state dynamics of similar flows.
>>> Thank you in advance!
>>> Outi
>>> _______________________________________________
>>> Nek5000-users mailing list
>>> Nek5000-users at lists.mcs.anl.gov
>>> https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users
>>>
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