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Old   May 27, 2004, 02:25
Default error in LES simulation
  #1
natesan
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When I try to run a LES problem I am getting run time error messages as follows;

START WALL DISTANCE CALCULATION CPU TIME IS 3.61 ELAPSED TIME IS 3.57 BEGINNING CELL TO WALL DISTANCE CALCULATION *** ERROR: NPEAK: 132 In box 4 3 1

SET MAXSC2 to atleast 132000

*** ERROR #020 *** TOO MANY CELLS IN NEAR-WALL LAYER.

SELECT A SMALLER SET OR INCREASE PARAMETER MAXSC2 IN parm.inc AND RELINK STAR.

The surprising fact is that dimension of the parameter MAXSC2 is about three orders higher than the value demanded in the above message. Can anybody help me in this problem. Can this problem be resolved by reducing the size of near wall set. If so, how can I achive it? Thanks in advance Natesan
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Old   May 27, 2004, 13:40
Default Re: error in LES simulation
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yacine
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Yea I had this problem some time ago I am not sure if it is a bug or not it usually happend when you hav some symmetry boundary in the case. The way around it is just to keep increasin the value of MAXSC2 till it accept it ! by the way are you using the new version 3.2 ? or an old version and what patch??
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Old   May 28, 2004, 01:34
Default Re: error in LES simulation
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natesan
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Yes I do have a symmetry boundary in my problem. The value of maxsc2 is already 110000000 and I am not able to increase it further. I am using 3.15 version of star cd. I tried the same case by coasrsening the mesh by increasing the size of two layers of cells near the walls to 10 mm size from the old 2 mm size. It is running successfully. Is this the right approach of solving this problem? I am solving the LES problem with fluid temperature calculation and without conjugate heat transfer and buoyancy. I am getting some unrealistic temperatures at few meshes during the transient. Is it because "star cd LES: is applicable for isothermal flow only? Please help me.
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Old   May 30, 2004, 22:30
Default Re: error in LES simulation
  #4
azmir
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Can't promise this will work but this has worked in my situation before. You were saying u can't increase the maxsc2 anymore, correct?

Try to delete your existing param.prp file. Make totally new param.prp file, increase the params gradually and resubmit. Sometimes, when I accidentally over-increased the maxsc2, star gave me this kind of error. When you re-make the param.prp this time, try to increase it gradually -- so that it will not overshoot some memory that your machine can't allocate.

I don't think this problem is LES-specific. Anyway, you can try but I can't promise success.
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Old   June 1, 2004, 06:22
Default Re: error in LES simulation
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Yacine
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The unrealistic values for the temperature are due to the convection scheme specially if you are using the centred scheme. If this values are bigger/smaller than the max/min values of about 30 % then you should use the MARS scheme but only for the temperature and central for the velocities. after the avereging you should be aible to check if this scalar overshout are afecting the flow by visualising the mean field. Notice that *.lesc *.lesr provide only mean and fluctuating variables for the velocities if you need the same for the tmeperature you'll hav to use postdat subroutine. If you need any more help on the matter email me and i can send you fortrans examples. good luck
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Old   June 1, 2004, 06:25
Default Re: error in LES simulation
  #6
Yacine
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I forgot to mention that with the version 3.15 basic the vandarist dampic function don't work and you may find stability problems with C-N scheme. try to get a newer patch like 35 or more.
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Old   June 2, 2004, 04:01
Default Re: error in LES simulation
  #7
alex
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You should upgrade to V3.2, since LES has been improved. The problem you are having sounds like a bug (which I am pretty sure has been fixed). Either, upgrade to the latest patch or V3.2.
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