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

equivalencing trouble

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

Reply
 
LinkBack Thread Tools Display Modes
Old   August 20, 2001, 23:32
Default equivalencing trouble
  #1
Steve Collie
Guest
 
Posts: n/a
I'm currently performing a 2D grid convergence study using cfx4.3. I'm having trouble generating fine grids in build. When I get down to around y+=1 equivalencing misses out a lot of nodes. Then when I try to manually equivalence I just end up collapsing near-wall elements. I've tried working in a larger scale but without any success. Any tips?

Cheers, Steve
  Reply With Quote

Old   August 21, 2001, 09:38
Default Re: equivalencing trouble
  #2
cfd guy
Guest
 
Posts: n/a
Steve,
Perhaps you should take a look at your global tolerance value in the geometry. If it is too large, build adjusts it automaticly for you, otherwise usually you get errors like those you mentioned.
Regards,
cfd guy
  Reply With Quote

Old   August 21, 2001, 18:04
Default Re: equivalencing trouble
  #3
Steve Collie
Guest
 
Posts: n/a
I've played around with the tolerance quite a bit and the adjusted tolerance (by build) is always very very small since my grid is small. As a consequence some nodes are not deleted during equivalencing. I had thought that rounding errors were my problem but when I redraw the block structure in micrometres instead of metres I get the same problem.

Thanks for your help, steve
  Reply With Quote

Old   August 21, 2001, 22:12
Default Re: equivalencing trouble
  #4
John C. Chien
Guest
 
Posts: n/a
(1). I had a lot of problems when using commercial codes to generate fine meshes, this included Fluent family, CFX-TASCflow family, ICEMCFD. (2). Since I don't know exactly how these codes create meshes from the geometry, it is hard for me to give advices. (3). My feeling is: the mesh is not created directly from known geometry, and there are some kinds of interpolation used in the process. (4). In principle, if you generate the geometry and the mesh together, you should be able to create mesh with no problem at all. (5). But if you create the geometry separately, and then try to generate a mesh, it is likely that you will have to use some kind of projection or interpolation. In many cases, the grid cross-over will result in mesh failure, if the two mesh line are very close together. (6). This is the place where users should try to write his own code to model the geometry and the mesh at the same time. (easy to say but hard to do I guess) In other words, mapping a mesh onto a geometry will likely create troubles,while it should be all right, if you calculate the mesh directly on the geometry.
  Reply With Quote

Old   August 22, 2001, 02:25
Default Re: equivalencing trouble
  #5
Astrid
Guest
 
Posts: n/a
When your geometry is simple, define your geometry in USRGRD. Then there is no limit but, yes I know, there is some work to do.

Astrid
  Reply With Quote

Old   August 22, 2001, 11:42
Default Re: equivalencing trouble
  #6
Jon
Guest
 
Posts: n/a
I think your problem is that you have some regions of very small cells in a relatively large geometry.

To get around this problem you should equivalence the problem area manually with a large tolerance, EXCLUDING the nodes which will be collapsed (the smallest cells).

This should get around your problem.
  Reply With Quote

Old   August 22, 2001, 18:26
Default Re: equivalencing trouble
  #7
Steve Collie
Guest
 
Posts: n/a
I agree, and have been equivalencing manually. Using this method I can equivalence the coarse cells OK. However equivalencing still fails when I try to equivalence the near-wall cells - where of course I need a small tolerance. Perhaps I need to try a different grid generator.

Thanks for your help, Steve
  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] trouble with mesh quality from ICEM in CFX Solver escher25 ANSYS Meshing & Geometry 0 February 28, 2011 08:38
[GAMBIT] Trouble meshing complex VOF geometry RPJones ANSYS Meshing & Geometry 2 February 14, 2011 19:54
Trouble migrating oodles to pisoFoam while changing from OF 1.5 to 1.7 sebi OpenFOAM 0 December 7, 2010 10:00
Parallel startup trouble! John CFX 9 April 22, 2005 20:17
trouble with fluxsum Jordi CD-adapco 2 September 29, 2000 03:57


All times are GMT -4. The time now is 10:18.