[Nek5000-users] Flow Rate Oscillation on 16384 cores

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

Dear All,

I have setup a simulation with Nek's constant flow rate option. The
simulation consisted of a number of restarts, in particular one restart was
carried out on 16384 cores whilst all the other runs where on 8192 cores.
In the plot of flow rate against dump in the following link, which I carry
out with my post-processor, the flow rate oscillates strangely in the
region where the run was on 16384 cores, i.e. between 220 and 343.

https://www.dropbox.com/s/fnfuqhj2nxbh5g5/FlowRate_restart_section.png?dl=0

Any idea on what might be causing this oscillation? All parameters,
geometry, machine settings etc. have been left the same for the run on
16384 cores (except for changing the max no. of processors and max no. of
elements per processor in SIZE).

Regards,
JP
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