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Making the density a function additional variab.

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Old   August 5, 2003, 13:09
Default Making the density a function additional variab.
  #1
Sebastien Perron
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Hi All,

I am a CFX 5 user and I am attempting to solve a flow where the "effective density" is a function of an additional variable. I am having all kind of troubles with it (I get by CFX-PRE but CFX-SOLVER crashes). Did anyone ever succesfully implemented such formulation in CFX 5?
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Old   August 6, 2003, 17:05
Default Re: Making the density a function additional varia
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jonathan
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Sebastien,

Doesn't the density have to be a function of the thermodynamic state of the fluid? Are you assuming ideal gas? What exactly do you mean by the "effective density"?

Perhaps I don't properly understand your problem, but maybe I can be of help with more information.

I am a relatively new CFX 5.6 user and am working on a somewhat similar problem (I want the additional variable to contribute to the overall pressure). I might be wrong, but I believe an additional variable is considered massless. Does anyone know if that is correct?

Jonathan
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Old   August 6, 2003, 19:32
Default Re: Making the density a function additional varia
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Sebastien Perron
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Jonathan, when the fluid is an ideal gaz, yes the density is thermodynamic variable and it is not a good idea to change it at will. But In my case, I am considering an incompressible fluid with a constant density. The "effective density" would me defined as rho*add_variable where the add_variable is a volume fraction. It is for a very special model.

I have tried several things with fortran subroutines, but it appears that CFX is in a way very well built: it may even crach when the density is a function of variables that are not built-in. (No there was not any bugs in my routines..).

I am about to consider another approach to implement my physical model.
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Old   August 8, 2003, 07:03
Default Re: Making the density a function additional varia
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Astrid
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Probably not the same, but we have used gases with densities that depended on P and T in a non-ideal way. Then we had to give in that density varied on 'Pressure' and 'Temperature'. I think CFX than makes a look up table for the different states. Just guessing, but could it be that your look up table is not generated automatically. Call your local representative...........

Astrid
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Old   August 8, 2003, 08:03
Default Re: Making the density a function additional varia
  #5
Sebastien Perron
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Hi Astrid,

I have tried making the density of function of pressure and tempereture: it works well. The only problem comes when the density is a function of an additional variable.

Thanks anyways.
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