[Nek5000-users] Using OIFS

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

Hi Alex,

Lowering your DT (parameter 12) slightly will keep a more stable courant
number and NEK won't blow up.


-Katie

On Thu, Aug 4, 2011 at 10:18 AM, <nek5000-users at lists.mcs.anl.gov> wrote:

> Alex,
>
> I see that p26 is set to 3 -- this is the target courant number -- which
> should be 2, no?  You might even make it smaller than that to start with.
>
> Also, for my nondimensionalization, I had
>
>  1.000000E+00 p054: direction of flow rate -- 1-X, 2-Y, 3-Z
>  12.56637E+00 p055: volumetric flow rate
>
> whereas you have
>
>   -1.00000     p054 fixed flow rate dir: |p54|=1,2,3=x,y,z
>   1.00000     p055 vol.flow rate (p54>0) or Ubar (p54<0)
>
> finally,  I have
>
>  4.000000E+00     p099 dealiasing
>  0.050            p103 filter weight of last mode
>
> whereas you have
>
>   3.00000     p099 dealiasing: <0--> off/3--> old/4--> new
>  0.100000E-01 p103 weight of stabilizing filter (.01)
>
>
> Let me know if making those changes helps.
>
> --Mike
>
>
>
>
> On Aug 3, 2011, at 3:41 AM, <nek5000-users at lists.mcs.anl.gov<mailto:
> nek5000-users at lists.mcs.anl.gov>> wrote:
>
> Hi neks,
>
> I'm trying to simulate a turbulent channel flow like in the presentation "A
> comparison
> of Nek5000 and OpenFOAM for DNS of turbulent channel flow" of Michael A.
> Sprague from the last
> user meeting (
> http://www.mcs.anl.gov/~fischer/nek5000/sprague_nek5000_dec2010.pdf"mid"-case).
> In the presentation it is mentioned that the CFL number is approx. 2 so I
> have choosen the BDF3/OIFS3
> scheme. However the solution blows up and Nek5000 stops the computation
> after 49 steps.
>
> Are there any parameters I have to set in the rea-file to get it work?
> TCHAR is true and p026 is
> set to 3. Dealiasing is turned on as well, but I'm not sure if the weight
> of the filter may be wrong.
>
> The files of the case are attached.
>
> Thanks!
> Alex
> <sprague3D.tar.gz><ATT00001..txt>
>
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