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

Discontinuity B.C UDF on coupled walls (Fluent)

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

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   March 24, 2020, 10:47
Default Discontinuity B.C UDF on coupled walls (Fluent)
  #1
New Member
 
Pablo Pasarín López
Join Date: May 2018
Posts: 7
Rep Power: 4
pablop is on a distinguished road
I have to create a boundary condition PROFILE in UDF, in which I can fix a UDSI value between two adjacent zones (like coupled walls) and at the same time create a discontinuity in the value of its flux. The trouble is that with only one interface (coupled walls) I can only set up one profile for fixing one of them.

I dont know if it is possible to create four adjacent interfaces for that purpose. Anyone has an idea?
pablop is offline   Reply With Quote

Old   March 24, 2020, 11:39
Default Coupled Boundary
  #2
Senior Member
 
vinerm's Avatar
 
Vinerm
Join Date: Jun 2009
Location: Nederland
Posts: 2,948
Blog Entries: 1
Rep Power: 31
vinerm will become famous soon enough
For the coupled walls, Fluent does not enforce conservation of flux. Those are just default conditions, for temperature as well as for UDS. User can choose different flux values on each side and even flux on one side and value on the other. Of course, then those are not coupled anymore.
__________________
Regards,
Vinerm

PM to be used if and only if you do not want something to be shared publicly. PM is considered to be of the least priority.
vinerm is offline   Reply With Quote

Old   March 24, 2020, 11:57
Default
  #3
New Member
 
Pablo Pasarín López
Join Date: May 2018
Posts: 7
Rep Power: 4
pablop is on a distinguished road
Thank you for your message

I know that coupled walls does not mean conservation, what I want to do is set conservation on the scalar and at the same time establish a different flux on the wall but I can only chose between Neumann and Dirichlet b.c condition. It would be like introducing a flux source on the interface
pablop is offline   Reply With Quote

Old   March 24, 2020, 12:06
Default Two Conditions
  #4
Senior Member
 
vinerm's Avatar
 
Vinerm
Join Date: Jun 2009
Location: Nederland
Posts: 2,948
Blog Entries: 1
Rep Power: 31
vinerm will become famous soon enough
You can separate first layer of cells from the interface and apply a source term. Applying both, value and flux, may lead to conservation issues. Assuming this UDS represents energy, then applying a temperature and a heat flux may not maintain flux conservation with the other boundaries. So, source at the cells could be one way.
__________________
Regards,
Vinerm

PM to be used if and only if you do not want something to be shared publicly. PM is considered to be of the least priority.
vinerm is offline   Reply With Quote

Old   March 24, 2020, 13:14
Default
  #5
New Member
 
Pablo Pasarín López
Join Date: May 2018
Posts: 7
Rep Power: 4
pablop is on a distinguished road
To clarify continuing with the energy equation analogy I should multiply the flux with the cell area and apply it as a source in the cell, no?

Thank you.
pablop is offline   Reply With Quote

Old   March 24, 2020, 14:31
Default Flux as source
  #6
Senior Member
 
vinerm's Avatar
 
Vinerm
Join Date: Jun 2009
Location: Nederland
Posts: 2,948
Blog Entries: 1
Rep Power: 31
vinerm will become famous soon enough
Whenever a source is applied, it is always a volumetric source. Fluent will multiply this value with the cell volume and then apply it. A big difference in flux and source is that the flux is a vector while source is not. However, since you will apply source adjacent to the interface, it will automatically create gradient depending upon the field value in the adjacent cells. As far as value is concerned, you may have to iterate over it since you may know the flux value but flux will depend upon gradient. So, you have to try a few values of the source before you get it right.
__________________
Regards,
Vinerm

PM to be used if and only if you do not want something to be shared publicly. PM is considered to be of the least priority.
vinerm is offline   Reply With Quote

Old   March 25, 2020, 04:51
Default
  #7
New Member
 
Pablo Pasarín López
Join Date: May 2018
Posts: 7
Rep Power: 4
pablop is on a distinguished road
I only know the difference in flux between the interface, so introducing this source which would represent the jump, should be sufficient. Ok thank you I will try
pablop is offline   Reply With Quote

Old   March 25, 2020, 04:55
Default The jump
  #8
Senior Member
 
vinerm's Avatar
 
Vinerm
Join Date: Jun 2009
Location: Nederland
Posts: 2,948
Blog Entries: 1
Rep Power: 31
vinerm will become famous soon enough
Yes, the source would create a jump, however, you will have to fine tune the value of the source so that you get the desired jump.
__________________
Regards,
Vinerm

PM to be used if and only if you do not want something to be shared publicly. PM is considered to be of the least priority.
vinerm is offline   Reply With Quote

Old   March 27, 2020, 05:34
Default
  #9
New Member
 
Pablo Pasarín López
Join Date: May 2018
Posts: 7
Rep Power: 4
pablop is on a distinguished road
Hi,
Thank you! It worked, by any chance do you know if it is possible to write a single source for momentum equation so that I can get the equation component from a macro, instead of writing 3 different sources for each component.
pablop is offline   Reply With Quote

Old   March 27, 2020, 06:29
Default Source Function
  #10
Senior Member
 
vinerm's Avatar
 
Vinerm
Join Date: Jun 2009
Location: Nederland
Posts: 2,948
Blog Entries: 1
Rep Power: 31
vinerm will become famous soon enough
Fluent doesn't care about what you write in source function and where do you hook. It will just use the values and apply it as source. So, you can hook same code as mass source, all three momentum source, energy source, etc.
__________________
Regards,
Vinerm

PM to be used if and only if you do not want something to be shared publicly. PM is considered to be of the least priority.
vinerm is offline   Reply With Quote

Reply

Tags
coupled, discontinuity, fluent, flux discontinuity, udf

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
My UDF works well with Fluent 16 but not with Fluent 19 Ahmed A. Serageldin Fluent UDF and Scheme Programming 3 October 19, 2018 11:38
can anyone help me about the udf of dynamic contact angle in FLUENT? Albert Lee FLUENT 0 July 1, 2018 08:21
Fluent UDF for thermal NOx larsschwarzer Fluent UDF and Scheme Programming 1 July 18, 2014 08:39
The fluent stopped and errors with "Emergency: received SIGHUP signal" yuyuxuan FLUENT 0 December 3, 2013 22:56
how to set such B.C. in Fluent? Sherri FLUENT 1 January 12, 2006 12:32


All times are GMT -4. The time now is 16:54.