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Scott Nordsen January 27, 2010 17:32

CFX Additional Variable Transport Equation
I am interested in implementing a turbulence model into CFX.

I have done so in Fluent using UDFs and UDSs and found it somewhat easy.

In CFX, it appears that I need to use Additional variables and Junction Boxes.

CFX help has nothing like the UDF manual in Fluent. So I am trying to piece together.

One issue was the junction box implementation. It seems there used to be a tutorial with mesh deformation and FSI that had this. But I do not see the files for CFX.

Any guidance on examples for this would be appreciated


ghorrocks January 28, 2010 17:33

Are you sure you can't do your model in CEL? The CEL in CFX is much more powerful than what is available in Fluent.

Scott Nordsen January 29, 2010 15:05

perhaps that would be best?

with fluent I am used to using a hook function that fills 30+ UDMs that are then used in the source calculations for my UDS

with CELs, I assume I would have to do a little more work in the setup portion (i.e. setup the expression for each "UDM")

if CELs are used for the additional variables are these updated in sequence after each iteration?

ghorrocks January 30, 2010 06:36

You have not described what you are modelling so I cannot say whether you can do it in CEL.

The Fluent UDM and UDS are additional variables in CFX. You have a few different options for how they are calculated - either an expression, a diffusion equation, a convection equation or diffusion/convection (there may be others but these are the ones I have used). At first glance a UDM is equivalent to an additional variable set by an expression, and a UDS is equivalent to an additional variable with a convection/diffusion equation.

From memory the CEL is updated before the coefficient loops. The CEL is not coupled into the equation solver, but any additional variables are (through a segregated solver).

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