[Nek5000-users] Mass flow rate and averages

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

If you set the mass flow (p54-55) in your periodic channel, the forcing as a function of time
can be found via:

grep vol logfile

will show lines like:


    1989 0.1989000E+01  3.72046E-02  3.99058E-05  1.99996E+00  2.00000E+00 volflow X

Column 1 is step number,
Column 2 is time.

Column 3 is the mean (in space) pressure gradient, as function of time.

This is the pressure gradient required to sustain a fix mass flow rate.

If you wish to instead prescribe mean pressure gradient, set p54 and 55 = 0 in the .rea
file and set ffx = 1 (say) in the .usr file.

To get the volumetric flow rate, you can do the following in userchk:

      n = nx1*ny1*nz1*nelv
      volf = glsc3(vx,bm1,n)/xlength

     where xlength is the domain length.  (This example assumes your
flow is in the x direction.

You can get xlength via:

      call domain_size(xmin,xmax,ymin,ymax,zmin,zmax)

     xlength = xmax-xmin

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: Wednesday, February 17, 2016 8:14 AM
To: nek5000-users at lists.mcs.anl.gov
Subject: [Nek5000-users] Mass flow rate and averages

Hi neks,
maybe my, will be noob questions, but i am a nek noob.
I am running a DNS of channel with riblets, now i  need to know the
averages fields and the mass flow rate.
For the averages fields i have seen in turbChannel example folder, and i
have seen in turbchannel.usr that there is a subroutine that do it.
But i didn't understand, if i set fintime(P10) and iotime(P14) and P68
in rea file, have i always the output?Because in turbchannel example, if
i set how i already told, i have errors in compilation.
And the second question is related to the mass flow rate.
If i set forcing, can i know the relative mass flow rate? Or viceversa,
if i set the mass flow rate in .rea file, can i know the forcing? Where
can i read or compute it?

Best regards
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