CFX Additional Variable Transport Equation

Scott Nordsen · January 27, 2010, 17:32

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

Thanks
Scott

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).

January 27, 2010, 17:32	CFX Additional Variable Transport Equation	#1
Scott Nordsen New Member Join Date: Jun 2009 Posts: 13 Rep Power: 17	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 Thanks Scott

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Is it possible to use divergence in the source term of an scalar transport equation?	jannnesss	CFX	0	January 8, 2010 20:53
Turbulent Heat Transfer Transport Equation	Flo.duck	Main CFD Forum	0	May 6, 2009 04:37
CFX - how to define custom scalr transport equatio	CFD user	CFX	0	February 20, 2009 14:09
Additional variable - wall boundary condition	flga	CFX	2	May 30, 2007 04:14
GETVAR SUBROUTINE for additional variable in CFX	Tuks	Main CFD Forum	0	November 8, 2005 07:13

January 28, 2010, 17:33		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,871 Rep Power: 144	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.

January 29, 2010, 15:05		#3
Scott Nordsen New Member Join Date: Jun 2009 Posts: 13 Rep Power: 17	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?

January 30, 2010, 06:36		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,871 Rep Power: 144	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).