CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > ANSYS Meshing & Geometry

2D Meshing - No matter how thin my model is, it is still 2 elements thick

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

Reply
 
LinkBack Thread Tools Display Modes
Old   March 30, 2010, 00:44
Default 2D Meshing - No matter how thin my model is, it is still 2 elements thick
  #1
Member
 
Join Date: Feb 2010
Location: Australia
Posts: 65
Rep Power: 7
RossFS is on a distinguished road
Context: Ansys Workbench, meshing for use with ANSYS CFX

With the default settings the mesh is all made of hexahedra elements and the model is 1 cell/element thick. As soon as I use inflation (which I need in the boundary layer) the elements above the inflation layers become tetrahedra elements and end up making the model 2 elements thick (as can be seen in an image below). This is definitely not a 1 cell thick model as I'm getting momentum and velocity components being calculated in the z direction during the solution.

I've even had the model 0.01mm thick and the mesh still ends up being 2 cells thick (like in the image below).

The cells above my inflation layers can be either tetrahedra or hexahedra in shape, but I have to have the model run as a 2D simulation.

Side on:



Iso view - red indicates location of close up that follows this


Close up:
RossFS is offline   Reply With Quote

Old   March 30, 2010, 13:16
Default Method?
  #2
Senior Member
 
PSYMN's Avatar
 
Simon Pereira
Join Date: Mar 2009
Location: Ann Arbor, MI
Posts: 2,662
Blog Entries: 1
Rep Power: 35
PSYMN has a spectacular aura aboutPSYMN has a spectacular aura about
What method are you using? You should be using something like the sweep method...

Note, if you do use the sweep method, the inflation setup is a little odd. Start with creating the sweep method, the "inflate this method" rather than creating a separate inflation. Also, when inflating a sweep, you pick the edges on the sweep face rather than the side surfaces.

Simon
PSYMN is offline   Reply With Quote

Old   March 31, 2010, 21:21
Default
  #3
Member
 
Join Date: Feb 2010
Location: Australia
Posts: 65
Rep Power: 7
RossFS is on a distinguished road
Thanks Simon.

Just to clarify the steps suggested by Simon for anyone looking at this thread from a search:

*bring up the mesh editing program/section in Workbench
*right click on mesh in the tree on the LHS of screen and click on: insert-> method
*select sweep from the 'Method' list that is in amongst the settings on the screen.
*follow the instructions for 'Inflation Controls with Sweeper' in the "Inflation Controls" help article [for meshing]
RossFS is offline   Reply With Quote

Old   March 31, 2010, 22:03
Default
  #4
Member
 
Join Date: Feb 2010
Location: Australia
Posts: 65
Rep Power: 7
RossFS is on a distinguished road
Any idea why I can't set the first layer thickness (when setting up the inflation) to be any lower than 4e-5m in height?
The mesh won't get created/an error occurs if I go any smaller than this.

Other settings for inflation are: 100 layers and a growth ratio of 1.032.

The smallest first layer thickness in a journal article I'm comparing against is something like 2.411e-7m high, with growth ratio of 1.032. Is that sort of size smaller than what ANSYS CFX can handle?
RossFS is offline   Reply With Quote

Old   April 1, 2010, 11:57
Default
  #5
Senior Member
 
PSYMN's Avatar
 
Simon Pereira
Join Date: Mar 2009
Location: Ann Arbor, MI
Posts: 2,662
Blog Entries: 1
Rep Power: 35
PSYMN has a spectacular aura aboutPSYMN has a spectacular aura about
RossFS,

This problem with the limited prism aspect ratio is fixed for 13.0... (Due out later this year)

The problem was only for the swept prisms (regular Tetra Prism did not have this limitation). Basically, there was a shape check limiting the aspect ratio for the quads used to sweep the inflation layer. This has been removed.

Sorry for the inconvenience.

Last edited by PSYMN; April 1, 2010 at 12:12. Reason: Clarified the problem that was fixed...
PSYMN is offline   Reply With Quote

Old   April 12, 2010, 03:11
Default
  #6
Member
 
Join Date: Feb 2010
Location: Australia
Posts: 65
Rep Power: 7
RossFS is on a distinguished road
So if I want to have a 2D mesh and want to inflate the boundary layer, do I have any other options than the Sweep method?

I ask as I'm wondering whether the size limitation mentioned above is the limit available on the sweep mesh method or whether it is the limit of the software. Or would I have to work in ICEM CFD to refine the mesh anymore near the bottom wall?

It is hard to tell from the help files on the different mesh methods what each of them do given my lack of understanding of CFD.
RossFS is offline   Reply With Quote

Old   April 14, 2010, 00:13
Default
  #7
Senior Member
 
PSYMN's Avatar
 
Simon Pereira
Join Date: Mar 2009
Location: Ann Arbor, MI
Posts: 2,662
Blog Entries: 1
Rep Power: 35
PSYMN has a spectacular aura aboutPSYMN has a spectacular aura about
No, sweep is for a 3D mesh (in this case, 2.5D). If you want a 2D mesh and you have a 2D model, that should work without sweep.

IF you did mean a 3D mesh, there are other options such as MultiZone and ThinSweep...
PSYMN is offline   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
[GAMBIT] Desperate student needs help meshing 3D GAMBIT model - please help! lau06165 ANSYS Meshing & Geometry 1 March 22, 2010 02:09
Problem with meshing long, thin faces in CFX Martin CFX 3 January 8, 2009 21:51
LES and combustion model Margherita Cadorin CFX 0 October 29, 2008 06:24
Element coordinates for momentum source model CFDworker CFX 3 October 10, 2007 11:05
Limitation of 2D and 3D model element number Soon CFX 3 January 30, 2006 16:15


All times are GMT -4. The time now is 19:20.