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

stoopid discontinuity

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

Reply
 
LinkBack Thread Tools Display Modes
Old   October 10, 2006, 07:04
Default stoopid discontinuity
  #1
Matthew R
Guest
 
Posts: n/a
Hi all, i'm quite the novice at CFD. I've used Gambit to generate my mesh but i have a really frustrating problem. When i import the mesh to Fluent and run a few iterations i see that flow does not occur across the boundarys of different volumes. ie flow goes into one section and stops as if it thinks it is a solid wall. For the life of me i can't determine how to fix this! I don't think i need to Fuse in Fluent. Strangely, if i do a little test in a new file with 2 simple volumes with different meshing and run it in Fluent this type of discontinuity doesn't exist, so why in my big mesh? It is very very frustrating...

Regards, Matt
  Reply With Quote

Old   October 10, 2006, 07:34
Default Re: stoopid discontinuity
  #2
manoj
Guest
 
Posts: n/a
it is possible bcz of wall between two volume u can ensure same by checking grid in fluent. how to slove it? 1) u can unite all geometry mesh it get the result 2)if u have used split command then check whether connected option is ON or not. hope this may be useful.
  Reply With Quote

Old   October 10, 2006, 07:54
Default Re: stoopid discontinuity
  #3
Jason
Guest
 
Posts: n/a
The faces between the geometry aren't connected... you have two options...

1) connect all the overlapping faces (i.e. the faces where the two volumes should share)... if you have all real geometry, you can highlight everything and hit connect... then manually check each face to make sure it's connected (i.e., there is only one face where the two volumes come together). You'll have to remesh, because currently the faces that you're going to connect have different meshes, so when you connect the faces, one of the face meshes will be destroyed

2) use non-conformal interfaces. That's the simplest. But non-conformal interfaces pose their own problems (i.e. numerical problems).

Hope this helps, and good luck, Jason
  Reply With Quote

Old   October 10, 2006, 22:42
Default Re: stoopid discontinuity
  #4
Matthew R
Guest
 
Posts: n/a
Hi guys thanks for the replies. Still battling with it however. I have tried the connect faces thing, but it hasn't worked. I think it's due to the nature of my geometry. Basically the problem occurs at the boundary of two cubes with the same dimensions, except the bottom cube has beveled corners. This mean that there are two faces at the interface: one square face and one square with the corners cut off. Can't Gambit connect these (connect the parts that do overlap) someway?

Also, why can't we attach a picture!

Regards, Matt
  Reply With Quote

Old   October 11, 2006, 01:42
Default Re: stoopid discontinuity
  #5
sach
Guest
 
Posts: n/a
I think your problem is; you have virtual volumes so it may not split in gambit the best way is non confirmal interfaces. do one check I think there may be omore than two volumes or dummy faces one should do the following once complete the volume mesh its best practice to confirm the 1) no of volumes present 2) delete the faces from entire geometry this will delete the hanging faces
  Reply With Quote

Old   October 11, 2006, 04:31
Default Re: stoopid discontinuity
  #6
Matthew R
Guest
 
Posts: n/a
Hmmm, i'm learning a lot..

What i was doing was meshing a volume, and then meshing the volume on top of it and thinking they would be connected...but i was using two different faces at the interface! I needed to construct the top volume using the face from the bottom for them to connect.

Of course once i figured this out, i found that the nice quad mesh that i could previously use would not work, since the mesh now had to work with the meshed face on the other volume.

What i have done is used a small amount of tet mesh as an interface between the two volumes, this enables me to use quad mesh for the rest of the shape...is this valid? Is this a better way than using something like Tgrid or the non-conformal meshes i've read about to make the interface?

Thanks again for the replies...i'm such a novice!

regards, -matt
  Reply With Quote

Old   October 11, 2006, 07:56
Default Re: stoopid discontinuity
  #7
Jason
Guest
 
Posts: n/a
I guess I should've asked for more details when telling you to connect faces, but I assumed that you had identical faces where the volumes come together.

Gambit can only connect faces if they are coincident, have coincident edges, and coincident vertices (i.e. are copies of one another within the tolerance).

If the faces are different, then use the non-conformal interface. If your mesh size is refined enough and consistent across the boundary (you can even use tet on one side and hex on the other... as long as they're of similar size).

The only other option is to split the larger face with the smaller one. Now the large face has a chunk cut from it that looks exactly like the small face. You can connect these, and then mesh.

There's a lot of other information on the forum about connected geometry, non-conformal meshes, etc. Do a search and see what you find.

Good luck, Jason
  Reply With Quote

Old   October 11, 2006, 09:37
Default Re: stoopid discontinuity
  #8
Matthew R
Guest
 
Posts: n/a
thanks for the help..looks like its finally working, -matt
  Reply With Quote

Old   October 11, 2006, 22:49
Default Re: stoopid discontinuity
  #9
sach
Guest
 
Posts: n/a
one more suggestion; its not so that you have to extrude the same face please see the details of volume split operation (its a binary operation )
  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
Rotor stator problem: Discontinuity across the interface Bubka CFX 2 November 11, 2009 08:57
Density discontinuity! Ilias FLUENT 0 September 17, 2004 08:04
My patch causes a discontinuity in the mesh Aline CD-adapco 5 July 7, 2004 07:45
Stepwise Discontinuity problem Alan Kang Main CFD Forum 1 February 23, 2000 00:46
Solid-Solid Heat Transfer with Contact Discontinuity Jonas Larsson Main CFD Forum 9 September 10, 1999 15:46


All times are GMT -4. The time now is 04:34.