[Nek5000-users] Using OIFS

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

Thanks for your replies!

I think, it works now. The flow looks good, but there is/was an error
in the post-processing part. The initialization made some problems and
the wrong wall size was in the userfile. I changed the parameters like
Mike suggested and took DT=0.02 what seems to be fine. I'm currently
running a simulation with param(12) = 0.034 so the time step size can
be varied by Nek. I hope the post-processing will do its job this
time.

Alex

2011/8/7 <nek5000-users at lists.mcs.anl.gov>
>
> PS --
>
> In the files I sent, I had a line:
>
>      ubar = glsum(vx,bm1,n)/volvm1
>
> which should read:
>
>      ubar = glsc2(vx,bm1,n)/volvm1
>
>
> Paul
>
>
> On Fri, 5 Aug 2011, nek5000-users at lists.mcs.anl.gov wrote:
>
>>
>> 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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