[Nek5000-users] Qustions about averaging for a 2D case
nek5000-users at lists.mcs.anl.gov
nek5000-users at lists.mcs.anl.gov
Thu May 27 10:34:27 CDT 2010
Hi,
I am running a 2D DNS simulation of backward facing step combustor with a
microjet. The microjet is placed on the step at 0.5H from the bottom wall.
The incoming velocity is U_o = 12.5 m/s and the microjet velocity is 25
m/s.
After running the case for 10 flow throughs, I started averaging over the
next 8 flow throughs. But the results for averaging don't exactly look
right. The geometry used and the averaged x-velocity colorfill contours
can be seen in the image at link below.
http://www2.uic.edu/~hkanch1/avg_mj10000.bmp
I have tried averaging twice, once over 5 flow throughs and other over 8
flow throughs. Both time getting similar results.
Here are the parameters that I am setting in the .rea file.
************************************************************************
103 Parameters from file:/home/harish/nek5_examples/2D_bfs/mj_2d/mj1.rea
1 1.00000 DENSITY
2 1.556e-5 VISCOS
4 1.00000 GTHETA
7 1.00000 RHOCP
8 0.100000E-01 CONDUCT
11 128000.00 NSTEPS
12 -0.0000010 DT
15 128000 IOSTEP
18 0.500000E-01 GRID
19 -1.00000 INTYPE
20 5.00000 NORDER
21 1.000000E-07 DIVERGENCE
22 1.000000E-09 HELMHOLTZ
24 0.100000E-01 TOLREL
25 0.100000E-01 TOLABS
26 2.000000 COURANT
27 3.00000 TORDER
28 0.000000E+00
49 0.000000E+00
66 4.00000 write form (0), unform(1), universal(2)
67 4.00000 read form (0), unform (1), universal(2)
93 20.00000E+00 Number of pressure sol'ns saved
94 5.000000E+00 start saving pressure soln's after this
95 5.000000E+00 start saving pressure soln's after this
99 3.00000 p99 = 3 --> dealias turned on
103 0.01 103 filter weight
IFTRAN = T
IFFLOW = T
IFHEAT = F
IFSPLIT = T
IFLOMACH = F
IFUSERVP = F
IFUSERMV = F
IFSTRS = F
IFCHAR = T
IFCYCLIC = F
IFAXIS = F
IFMVBD = F
IFMELT = F
IFMODEL = F
IFKEPS = F
IFMOAB = F
IFSYNC = T
************************************************************************
At the outflow, I am using the "fill_div(usrdiv)" subroutine provided in
the "peris.usr" example. Is it possible the value of "vnmo_desire = 5.0",
that I set, is too high? I choose this value because at lower values the
simulation would blow up. Is there a way to calculate this value based on
incoming velocity?
Thanks for all the help,
Harish
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