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

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

Thanks! Indeed this is what happens, we seem to have mixed up the mean  
flow development and the disturbance development....
So, I am sorry for bothering you but happy that all is correct.
Outi

Quoting Outi Tammisola <outi at mech.kth.se>:

> Hi Paul,
>
> As far as I can see, the userbc is set only at the inlet. The first  
> probe point is at z=3, that is, 6 diameters downstream of the inlet  
> (after transformation in usrdat2 from -3 to 10). What concerns me is  
> that the z-velocity goes up to 0.48e-1 at z=3 at the first time  
> step, when the inflow hasn't reached near this point yet. When I  
> output the whole velocity field at the first time step (as .f00001)  
> and look at it in paraview, the z-velocity has oscillations near the  
> throat. Maybe at the end this is some transient phenomenon which  
> doesn't matter, but I thought it was safest to check with you.
>
> Best,
> Outi
>
> Quoting 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
>>>>>
>>>> _______________________________________________
>>>> Nek5000-users mailing list
>>>> Nek5000-users at lists.mcs.anl.gov
>>>> https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users
>>>
>>> _______________________________________________
>>> Nek5000-users mailing list
>>> Nek5000-users at lists.mcs.anl.gov
>>> https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users
>>>
>> _______________________________________________
>> Nek5000-users mailing list
>> Nek5000-users at lists.mcs.anl.gov
>> https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users