CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Software User Forums > ANSYS > CFX

Additional variable

Register Blogs Members List Search Today's Posts Mark Forums Read

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   July 20, 2012, 09:07
Default Additional variable
  #1
New Member
 
Luigi Gurreri
Join Date: Jul 2012
Posts: 18
Rep Power: 13
Luigi is on a distinguished road
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?
Luigi is offline   Reply With Quote

Old   July 20, 2012, 15:07
Default
  #2
Member
 
Felggv's Avatar
 
Felipe Gobbi
Join Date: Apr 2012
Location: Brazil
Posts: 76
Rep Power: 13
Felggv is on a distinguished road
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: http://www.cfd-online.com/Forums/cfx...ple-solve.html

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
Felggv is offline   Reply With Quote

Old   July 20, 2012, 19:16
Default
  #3
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,665
Rep Power: 143
ghorrocks is just really niceghorrocks is just really niceghorrocks is just really niceghorrocks is just really nice
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.
ghorrocks is offline   Reply With Quote

Old   July 22, 2012, 15:46
Default Where is the RULES file?
  #4
New Member
 
Luigi Gurreri
Join Date: Jul 2012
Posts: 18
Rep Power: 13
Luigi is on a distinguished road
Thanks for your help,

but where can I find the RULES file??
Luigi is offline   Reply With Quote

Old   July 22, 2012, 17:35
Default
  #5
Member
 
Felggv's Avatar
 
Felipe Gobbi
Join Date: Apr 2012
Location: Brazil
Posts: 76
Rep Power: 13
Felggv is on a distinguished road
It should be here:

C:\Program Files\ANSYS Inc\v130\CFX\etc
Felggv is offline   Reply With Quote

Old   July 23, 2012, 07:45
Default Simulation is running
  #6
New Member
 
Luigi Gurreri
Join Date: Jul 2012
Posts: 18
Rep Power: 13
Luigi is on a distinguished road
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!!
Luigi is offline   Reply With Quote

Old   July 23, 2012, 10:28
Default
  #7
Member
 
Felggv's Avatar
 
Felipe Gobbi
Join Date: Apr 2012
Location: Brazil
Posts: 76
Rep Power: 13
Felggv is on a distinguished road
Luigi,

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
Felggv is offline   Reply With Quote

Old   July 23, 2012, 10:52
Default
  #8
New Member
 
Luigi Gurreri
Join Date: Jul 2012
Posts: 18
Rep Power: 13
Luigi is on a distinguished road
As I can see from preliminary results, it semms to work well!
Luigi is offline   Reply With Quote

Old   March 26, 2019, 15:29
Default
  #9
New Member
 
Join Date: Oct 2018
Posts: 17
Rep Power: 7
NewToAnsys is on a distinguished road
In such a case, where one of the material properties of the domain is dependent on another variable (which has been added to the dependency list of the property in the RULES file), an analysis that normally could be run at steady state would have to be transient right? Since the material property of the domain is changing, at least initially?
NewToAnsys is offline   Reply With Quote

Old   March 26, 2019, 17:51
Default
  #10
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,665
Rep Power: 143
ghorrocks is just really niceghorrocks is just really niceghorrocks is just really niceghorrocks is just really nice
As discussed on the other thread - no, changing material properties does not mean you need a transient simulation.
__________________
Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.
ghorrocks is offline   Reply With Quote

Reply

Tags
additional variable, kinematic diffusivity

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Condensation as an additional variable Clark Griswold CFX 2 April 21, 2012 08:20
emag beta feature: charge density charlotte CFX 4 March 22, 2011 10:14
Problems with additional variable Krishna Premi CFX 1 October 29, 2007 09:19
Multi_component Vs Additional Variable Anurag CFX 2 February 4, 2005 17:45
Replace periodic by inlet-outlet pair lego CFX 3 November 5, 2002 21:09


All times are GMT -4. The time now is 13:10.