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

shadow boundaries?

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

Reply
 
LinkBack Thread Tools Display Modes
Old   June 20, 2003, 12:40
Default shadow boundaries?
  #1
jx
Guest
 
Posts: n/a
Hi, there,

I build a mesh with GMABIT2.0.4, which contains a solid block surrouding by the fluid area (2D).

When exporting the mesh, I found some extra boundaries generated, with "-shadow" suffix for their names. These seem to duplicate the surface of the solid block.

What are those boundaries? How should I treat them? I seem not able to delete them. Should I specify the BC for them in FLUENT?

Many thanks,

jx
  Reply With Quote

Old   June 20, 2003, 13:03
Default Re: shadow boundaries?
  #2
jx
Guest
 
Posts: n/a
Sorry, I just searched the forum and found some explanations for these shadow boundaries.

Now I have one thing not sure about:

What is the point to specify a different BC for a shadow'ed face from its original one, since physically they are the same?

Also, do I have to explicitly specify the same BCs for both the original face and its shadow, if I don't have special need to use different BCs for them?

Thanks,

jx

  Reply With Quote

Old   June 20, 2003, 22:14
Default Re: shadow boundaries?
  #3
lee
Guest
 
Posts: n/a
I think that is because fluent calculate the solution at cell (cubic) center. The wall is located on the face, so there are must 2 cell centers in each side of the face. One is inside of fluid and one is inside of solid. Actually there should be no value calculated on the wall.
  Reply With Quote

Old   June 21, 2003, 04:52
Default Re: shadow boundaries?
  #4
jx
Guest
 
Posts: n/a
Thanks for your time,lee.

Sure I understand the calculation is cell center based. But that does not necessarily mean the actual BC should also be based on cell centers. I am not sure how fluent specify the BCs, but when I do my own coding, I convert the mathematical restraint from faces to the cell center (by interpolations), for both sides of a boundary where appropriate. So essentially the BCs are specified right on the faces, just practically they are implemented on the adjacent cell centers. -- this way, it does not make sense to specify different BCs, in fluent, for those walls and their shadows.

Do I understand this correctly? (or, again, what is the point to specify different BCs for a wall and its shadow?)

Someone enlightens me, please?

jx
  Reply With Quote

Old   June 22, 2003, 04:44
Default Re: shadow boundaries?
  #5
Rahul HIwale
Guest
 
Posts: n/a
Jx what lee said it is correct. I would like to add this to it. Shadow wall will get created only at junction of fluid and solid. If you open that wall in BC panel in Fluent you can see adjacent cell zone (either flid or solid.) As you might be knowing in CHT problems temp on each side (same wall but on fluid or solid face) will be different. This shadow option help us to get it. It can be used for other special cases by removing coupled option and specifying temp or heat flux to either side if you know it. I hope your doubt is clear now. Rahul
  Reply With Quote

Old   June 24, 2003, 12:44
Default Re: shadow boundaries?
  #6
Anton
Guest
 
Posts: n/a
You can also have a shadow zone created when a wall of zero thickness splits a fluid zone. So in this case, you have two fluid zones on either side of the zero thickness wall. In such a problem you may want to have different boundary conditions on each side of that wall. For example, you may want to use a different emissitivity on each side in a radiation problem.
  Reply With Quote

Old   June 29, 2003, 04:44
Default Re: shadow boundaries?
  #7
jx
Guest
 
Posts: n/a
Thanks all for your responses. I get some understanding now.
  Reply With Quote

Reply

Thread Tools
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 On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
[ICEM] Shadow walls in Fluent. ICEM meshes vs Workbench aarvay ANSYS Meshing & Geometry 10 February 5, 2014 12:17
Setting Flow/Pressure Boundaries in Floworks Eran FloEFD, FloWorks & FloTHERM 3 August 11, 2009 04:23
periodic boundaries - flow through a net PK FLUENT 0 July 12, 2007 11:58
Periodic Boundaries in GAMBIT!! swetha FLUENT 1 November 26, 2006 23:02
mass flux correction at outflow boundaries Subhra Datta Main CFD Forum 2 November 24, 2003 14:11


All times are GMT -4. The time now is 21:34.