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Fire Dynamics Simulator
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Increasing of temperatur in eddies #2366

Closed gforney closed 9 years ago

gforney commented 9 years ago 
Please complete the following lines...

FDS Version:6.1.2
SVN Revision Number:20564
Compile Date:Fri, 26 Sep 2014
Smokeview Version/Revision:6.1.12
Operating System:Linux/Ubuntu 14.04

Describe details of the issue below:

A flow of air coming from the left side circulates around an obstruction. This leads
to the formation of eddies. As seen in the enclosed figure the temperature in the eddies
is unrealistic high although there is no heat source.

Herbert

Original issue reported on code.google.com by he.tauber on 2015-04-20 10:32:38

gforney commented 9 years ago 
I do not see this behavior with the current release (6.2.0).

Original issue reported on code.google.com by drjfloyd on 2015-04-20 12:12:26

gforney commented 9 years ago 
Now with the current release (6.2.0) it does work. But at parallel running I still see
this behavior (fds_mpi)

Original issue reported on code.google.com by he.tauber on 2015-04-21 05:50:41

gforney commented 9 years ago 
Your domain is 30 m high. By default, FDS assumes that the atmosphere is stratified.
That is, the pressure and density decrease with altitude. This causes small temperature
fluctuations, as would be expected in an outdoor flow. If you don't want this effect,
set STRATIFICATION=.FALSE. on the MISC line.

Original issue reported on code.google.com by mcgratta on 2015-04-21 18:23:33

gforney commented 9 years ago 
I set STRATIFICATION=.FALSE. on the MISC line, but the behavior still remains. This
effect starts at a wind velocity of about 0.7 m/s. When I set the temperature range
from 19.99 to 20.01 the effect starts at about 127 s and builds up. As seen in the
attached file you get a strange pattern.

This effect I noticed in some other simulations when the mesh cells were on the order
of a millimeter. By setting DNS=.TRUE. the behaviour was not seen anymore.

Original issue reported on code.google.com by he.tauber on 2015-04-22 08:13:19

gforney commented 9 years ago 
In any numerical solution of partial differential equations there will be some numerical
error. The error in FDS is second order in space. An error on the order of 0.01 K given
a 0.5 m grid size does not seem unreasonable.

Original issue reported on code.google.com by drjfloyd on 2015-04-22 12:29:49

gforney commented 9 years ago 
The file Eddies_0637.jpg shows only the beginning of the strange behavior but as you
can see in figure Eddies2.jpg it grows to an error on the order of about 15°C (17 to
32°C).

Original issue reported on code.google.com by he.tauber on 2015-04-23 05:56:27

gforney commented 9 years ago 
Running with the release version of 6.2.0 on Windows I cannot reproduce this. For the
case in comment #4 I show temperatures = 20 C for the length of the simulation for
both serial (1 process 4 threads) and mpi (2 processes 4 threads/process).

Original issue reported on code.google.com by drjfloyd on 2015-04-23 13:30:15

gforney commented 9 years ago 
I get this problem only at parallel running (fds_mpi) in Windows as well in Linux. In
the attached file you see the recorded min and max temperatures from the total area.

Original issue reported on code.google.com by he.tauber on 2015-04-24 06:01:51

gforney commented 9 years ago 
After studying User's Guide about "Numerical Stability Parameters" I tested a few parameters.
By changing the following parameters the problem was solved:

CFL_VELOCITY_NORM=1 or
FLUX_LIMITER=0 or
FLUX_LIMITER=5

Could you please confirm (correct) that I have to consider anyone of these parameters
for the parallel running.

Original issue reported on code.google.com by he.tauber on 2015-04-24 08:47:18

gforney commented 9 years ago 
There is no fds_mpi for FDS 6.2.0, there is only one executable for FDS now.  If you
are running fds_mpi, then you are using 6.1.2 or earlier.  I cannot replicate your
issue with FDS 6.2.0.

Original issue reported on code.google.com by drjfloyd on 2015-04-24 11:16:59

gforney commented 9 years ago 
If 6.2.0 was properly installed, fds_mpi.exe will be the same as fds.exe. It is just
a pointer. We did this to prevent old versions of fds_mpi from running. In any case,
type 

fds

or 

fds_mpi

to see what version you have.

Original issue reported on code.google.com by mcgratta on 2015-04-24 12:32:08

gforney commented 9 years ago 
I think one of the things you are experience is that you haven't changed the default
lapse rate from 0 C/m.  In typical usage, how we base our defaults, where one is dealing
with flows in buildings, there isn't a temperature lapse as heating and cooling systems
prevent it.  In atmospheric flows there is a drop in temperature with height.  The
attached images are your eddies2 case with the default LAPSE_RATE=0 (eddies2) and setting
an adiabatic lapse (eddies3) [LAPSE_RATE=-0.0098].  Note with the adiabatic lapse that
you don't see odd temperature behavior.  With no lapse, when higher density air at
the bottom is forced up into a lower pressure region it expands and cools (and vice
versa).  This causes what you saw in comment 2.  With  an adiabatic lapse, the cooling
by expansion is match by the drop in temperature with height and the temperature profile
remains constant.

Original issue reported on code.google.com by drjfloyd on 2015-04-24 14:13:11

gforney commented 9 years ago 
Now I see the problem. Last week I updated to the latest release. When I type fds I
get the version 6.2.0 and when I type fds_mpi I get the version 6.1.2. That means that
I always did the parallel run with the back version (fds_mpi). Now, when I do a parallel
run by typing: "mpiexec -n 2 fds Eddies.fds" I get the right result according to your
figures. If I got you right I do not have to use the fds_mpi file anymore. Am I right?

Original issue reported on code.google.com by he.tauber on 2015-04-27 13:59:58

gforney commented 9 years ago 
Yes. I suggest that you uninstall FDS, and then reinstall 6.2.0. This will remove old
executables. Or just type the name of the executable before running a job to ensure
you have the right version.

Original issue reported on code.google.com by mcgratta on 2015-04-27 14:02:51

gforney commented 9 years ago 
I uninstalled FDS and reinstalled 6.2.0 as you suggested. As far as I can see the wrong
version was the only reason for the behaviour. Finally I thank you for your help to
find out the answer.

Original issue reported on code.google.com by he.tauber on 2015-05-04 04:35:59

gforney commented 9 years ago 
Thanks for letting us know.

Original issue reported on code.google.com by mcgratta on 2015-05-04 12:04:06