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Old   March 2, 2001, 14:49
Default negative scalars !
  #1
Ossi Kaario
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Hi,

I observe very often in transient engine runs that I have negative scalar values for the injected fuel, CO2, and H2O ! This, of course, does not stabilize the runs...

I use the switch 78 to eliminate them but I think it does not help.

Any comments or suggestions ?

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Old   March 5, 2001, 08:45
Default Re: negative scalars !
  #2
allan
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are you using mars or ud to solve the scalers? I've had problems with scalers > 1 using mars, ud appeared to clear it. Also what are your inlet boundary conditions? If they are fixed mass try fixed velocity.
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Old   March 5, 2001, 10:09
Default Re: negative scalars !
  #3
stefan
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Try using constant 64: Setting rcon 64 to 1 clips the scalars between 0 and 1 for density calculation only, rcon 64 2 additionally clips the scalar values. (This seems to work only for active scalars.)
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Old   March 8, 2001, 15:36
Default Re: negative scalars !
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Ossi Kaario
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Thanks for your suggestions.

I do not have an inlet or outlet. To change from MARS to UD is maybe not so good because then you also decrease the accuracy of your solution.

Stefan, do you mean that the rcon 64 2 clips active scalars that are transported ? I.e. scalars defined as 'off' are not clipped ?

Regards,

Ossi
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Old   March 9, 2001, 02:14
Default Re: negative scalars !
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stefan
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I had a passive scalar and it was not clipped. I switched to active, and then it worked.
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Old   March 13, 2001, 14:51
Default Re: negative scalars !
  #6
Ossi Kaario
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I currently use the rcon 64 2 but it still give me warnings all the time in the *.info file that some of the scalars have values less than zero !?? (WARNING #009 ***THE VALUE OF SCALAR SC4 IN CELL 30609 ( -3.2635E-05) IS BELOW THE MINIMUM ( 0.0000E+00) )

I wonder why is it not working ?

Regards,

Ossi
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Old   March 13, 2001, 15:33
Default Re: negative scalars !
  #7
Ossi Kaario
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I just figured out that it might be that only the Transported scalars are limited between zero and one. The scalar I mentioned in the earlier mail was Active but not Transported (it was Internal).

Consequently, I wonder how could I limit the Internal scalars (which are Active) ?

Regards,

Ossi
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Old   March 14, 2001, 02:26
Default Re: negative scalars !
  #8
stefan
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Sorry, I don't know. You should call the CD hotline.
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