[Nek5000-users] Writing data files with lower lx during runtim e

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

Hi,

To dump out files on a coarser GLL mesh during runtime, I modified subroutine
mfo_outfld in prepost.f (find attached), and use map_m_to_n to interpolate.
Then I add these lines to usrchk:

      common lxnew
      integer useriostep,lxnew
      lxnew=8
c---  If lxnew is common, integer and > 2, and if param(66)=6, and
ifreguo=.false., a modification in subroutine mfo_outfld(prefix)
c---  in prepost.f will be activated when dumping data (either through iostep,
outpost or prepost) that maps all fields onto a coarser
c---  GLL mesh where lxnew-1 is the new polynomial order.

      useriostep=10 !Delta time step for interpolated output
      param(66)=6

c-----Parameters for IO, etc.
      if ((modulo(istep,useriostep).eq.0.).and.(istep.gt.1.)) then
        if (istep.gt.useriostep) ifxyo = .false.  ! Turn off xyz output
        ifreguo= .false. ! Maintain GLL mesh for later (spectral) post
processing.
        ! dump results into file
         call prepost(.true.,'coa') !
      endif
c-----The following is done for the last dump
      iostep = param(11) ! Dump on original grid at very last time step (to have
a restart solution)
      ifxyo = .true. !To ensure that geometry is dumped with restart file after
last time step
      param(66)=4. !To output last file on uncoarsened grid

The last 3 lines will ensure that at the end of the run, a data file is dumped
with the "original"/fine resolution to serve as a restarting point.

The attached pictures show a comparison of the stagnation region of an internal
flow (temperature contour and velocity vectors) on the original and a coarser
(lx1=8 instead of 14) grid. The vectors are interpolated on an evenly spaced
grid in both cases by VisIt.

As far as the motivation for this goes, I'd like to give some background info on
what we intend to do ("we" is Dr. Andrew Duggleby's research group (FT2L) at
Texas
A&M). We are running simulations of high Reynolds number, high free stream
turbulence intensity flow in complex geometries (turbine blades) with heat
transfer. The grid size for my problem is about 250 Mio points. In order to
analyze the data, we have a set of in house proper orthogonal decomposition
routines. They all require time correlations of snapshots (up to 1000 data
samples), to be read into memory multiple times. Since we only look at the lower
order
representation, a coarser grid than the simulation is running on supposedly
suffices for
that and makes these many file reading operations feasible on the resources we
have.
Since I intend to do the post processing with Nek, I wanted to maintain the GLL
mesh distribution.

I would be happy to hear any comments,
Markus Schwaenen

http://www1.mengr.tamu.edu/FT2L
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