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

Adding extra terms in governing equations

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

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   January 30, 2014, 11:21
Default Adding extra terms in governing equations
  #1
New Member
 
Smith
Join Date: Jan 2014
Posts: 9
Rep Power: 12
Alek is on a distinguished road
Dear friends,
Is it possible in CFX to add one or two extra terms in to governing equations? for example adding pressure gradient term to energy equation and CFX solves the modified energy equation containing pressure gradient term.

Sincerely
Alek is offline   Reply With Quote

Old   January 30, 2014, 18:02
Default
  #2
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 cannot modify the underlying equations. Your options are:
* If you can write it as a source term then use a source term
* Find an existing CFX physical model which is close and use that.
ghorrocks is offline   Reply With Quote

Old   January 30, 2014, 23:26
Default
  #3
New Member
 
Smith
Join Date: Jan 2014
Posts: 9
Rep Power: 12
Alek is on a distinguished road
Thank you Glenn,
In your idea can we present the pressure gradient as a source term ?

Sincerely
Alek is offline   Reply With Quote

Old   January 31, 2014, 00:05
Default
  #4
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
Yes, you certainly can use the pressure gradient in a source term. You can get the gradient of the pressure field with p.grad, and I think to get the components it is p.grad_x.
ghorrocks is offline   Reply With Quote

Old   January 31, 2014, 17:51
Default
  #5
Senior Member
 
Join Date: Jun 2009
Posts: 1,788
Rep Power: 31
Opaque will become famous soon enough
Dear Alek,

I am bit puzzled by your question. What heat transfer model are you using Thermal Energy, or Total Energy ?

If you are using the Thermal Energy model, I wonder what are you trying to achieve? What type of material are you using ? incompressible ? I would suggest to contact ANSYS support and check if there is already a mechanism to activate such term.

In the case of the Total Energy model, CFX already include the pressure gradient term; therefore, you may be double accounting such effect.

Still puzzled
Opaque is offline   Reply With Quote

Old   January 31, 2014, 23:26
Default
  #6
New Member
 
Smith
Join Date: Jan 2014
Posts: 9
Rep Power: 12
Alek is on a distinguished road
Dear opaque
In fact I want to add pressure gradient term to species transport equation. My problem is compressible.

Sincerely
Alek is offline   Reply With Quote

Old   February 10, 2014, 13:21
Default
  #7
Senior Member
 
Join Date: Jun 2009
Posts: 1,788
Rep Power: 31
Opaque will become famous soon enough
Dear Alek,

CFX nor FLUENT include the pressure gradient term in the species diffusion flux. FLUENT includes the thermal diffusion gradient though.

Keep in mind these additional terms are not trivial volumetric sources, but fluxes about the control volumes and must be discretized accordingly.

You may need to contact ANSYS (CFX / FLUENT) for support on how to implement such terms.
Opaque is offline   Reply With Quote

Reply

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
chtMultiRegionSimpleFoam samiam1000 OpenFOAM Running, Solving & CFD 39 March 31, 2016 09:43
Adding two Energy Equations to Porous Solver Filankes OpenFOAM Programming & Development 2 December 3, 2013 06:20
Axi-Symmetric governing equations Cary Turangan Main CFD Forum 0 November 25, 1999 16:44
Turbulent terms in the MRF equations Francisco Saldarriaga Main CFD Forum 1 July 22, 1999 17:49
1D governing equations Andrei Chernousov Main CFD Forum 5 July 13, 1999 16:06


All times are GMT -4. The time now is 05:48.