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Luigi July 20, 2012 08:07

Additional variable
I should run simulations in which the kinematic diffusivity is a function of the additional variable itself. In particular, the concentration of a solute is the additional variable, of which I have to solve the transport equation, and its diffusivity is a function of the concentration itself. The Solver reports this error message:
Error processing expression 'Kinematic Diffusivity'.
The expression is invalid because:
Concentration is not available for use in this term

Error processing expression: Kinematic Diffusivity = D.

Does it mean that is impossible to set the kinematic diffusivity as a function of the additional variable??
If not, how can I avoid this error?
If so, is there any chance to solve the problem?

Felggv July 20, 2012 14:07

Hi there,

I had the same message but with a different variable.

I wanted to calculate Temperature using the Mass Fraction, but in CFX, the mass fraction of a component cannot be used to calculate temperature in the default configurations of the CFX.

What I was told to do was to add this variable to the "default" by modifying the RULES file in CFX>etc folder, and I was properly warned by people here that mf was not set as default for a good reason, so if that's your solution for the problem, you should backup this file and monitor the results.

Here's the topic where they've helped me:

There's another way to solve the problem by adding a line of CCL command instead of modifying the RULES, it's post #15 there.

I'm not sure, but I think you don't have to create another variable since concentration is already there. If your problem is like mine, you should just enable it to use for you purpose.

Sorry for the long text

ghorrocks July 20, 2012 18:16

You can work around this by editting the rules file (see Felipe's link for this) but be aware that it is not supported by default because something is missing - it might not work at all, it might be completely wrong or it might give incorrect results in a very specific setup. What I am trying to say is it is not supported and you have to do your own checks to make sure it is working correctly.

Luigi July 22, 2012 14:46

Where is the RULES file?
Thanks for your help,

but where can I find the RULES file??

Felggv July 22, 2012 16:35

It should be here:

C:\Program Files\ANSYS Inc\v130\CFX\etc

Luigi July 23, 2012 06:45

Simulation is running
Thank you,
I have modified the RULES file and the simulation run, but this message appears:
Invalid entries in Dependency List for Kinematic Diffusivity have been found. Please ensure entries are defined in the VARIABLES file

I think that it is not a problem.

Anyway, thanks a lot! Now I can carry out my simulations!!

Felggv July 23, 2012 09:28


As some guys have warned me here, check out the results to see if they're not absurd because of the modification.

Hope it works well

Luigi July 23, 2012 09:52

As I can see from preliminary results, it semms to work well!

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