[Nek5000-users] Using OIFS

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

Hi Alex,

The issue seems to be that the given initial conditions lead
to high CFL numbers at early times, which is why the code
was blowing up.

It looks like your case will work if you just set dt > 0,
(param 12 in the .rea file).

This will allow the variable dt to kick in and will keep
the CFL number in the proper range, and at all times will
keep dt =< .034, your chosen value.

Also, I noticed a small bug in the .usr file, which I have
now fixed in the examples/ directory.  There should be no
call of the form:

    call avg1(ffx_avg,ffx_new,alpha,beta,1,'ffxa',ifverbose)

The routine avg1() is designed to work on arrays, whereas
ffx_avg and ffx_new are scalars.

It's unclear what the consequences of the call are -- they
would vary from one platform to the next, but could result
in undesirable memory overwrites.

Paul

PS - attached is a set of files that should work.

On Wed, 3 Aug 2011, 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
>
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