[Nek5000-users] Flow Rate Oscillation on 16384 cores

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

Hi JP,

Are you using p54 and p55 in the .rea file to set the flow rate to a fixed value?

This is by far the best approach to doing so for periodic bcs.

Paul

________________________________________
From: nek5000-users-bounces at lists.mcs.anl.gov [nek5000-users-bounces at lists.mcs.anl.gov] on behalf of nek5000-users at lists.mcs.anl.gov [nek5000-users at lists.mcs.anl.gov]
Sent: Saturday, March 28, 2015 2:10 PM
To: nek5000-users at lists.mcs.anl.gov
Subject: Re: [Nek5000-users] Flow Rate Oscillation on 16384 cores

Hi JP,
Yes, but I was just thinking that the fact that you do not recover an
exactly constant flow rate, while the algorithm in Nek in principle
assures exact constancy, might have something to do with your problem.
If you check the output of Nek (the logfile), there should be a line
with the computed flow rates and the forcing amplitude (the line ends
with something like "volflow"). Could it be that your postprocessing
routines are somehow affected by the different numbers of processors?

philipp

On 2015-03-28 20:01, nek5000-users at lists.mcs.anl.gov wrote:
> Dear Philipp,
>
> The slight flow rate variations are probably due to quick way we
> calculate the flow rate.. this is calculated on custom files that
> contain data which was converted from the original nek dumps.. the mesh
> spacing is not constant in the y direction and probably causes some
> oscillations.. what I cannot understand is how changing the number of
> cores affects this oscillation so much in the region where more cores
> were used...
>
> Regards,
> JP
>
>
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