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

Mesh generation -purpose of tetra transition

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

Reply
 
LinkBack Thread Tools Display Modes
Old   October 24, 2012, 11:27
Default Mesh generation -purpose of tetra transition
  #1
Member
 
Join Date: Jun 2011
Posts: 48
Rep Power: 6
eishinsnsayshin is on a distinguished road
Hello everyone,

I don't have the greatest background in mesh generation algorithms and am relatively new with CFD in the automotive industry. I've just recently begun to mess with Hexa-interior mesh using ANSA for its benefits such as flow alignment and mesh size reduction.

Take the example of a rectangular box, surface meshed entirely with quads. Wall conditions on the sides, an inlet, and an outlet. Pretty simple model! Using this, I've noticed that if you have a quad surface element, and you do a "hexa interior" or "hexa poly" volume mesh, pyramids will be used on each of those quad surface elements, followed by a few tetras to transition to the actual hexa elements. These tetras make a nice "squared off" flat surface for each of the hexas to go on such that their edges are aligned with the flow. I've also noticed ANSA will use tetras/polys at times if you have specified a growth rate for your hexas to transition between the different hexa sizes (kind of obvious...it has to use something)

Now, lets say I wanted my rectangle domain volume meshed completely with hexas. Is there a way in ANSA to do this? I am specifying a growth rate of 1 (so...no growth). Using quad surfaces for the inlet, outlet and sides still will result in pyramids on the surface elements, a few tetras, and then perfect little cube hexas of the same size all the way to the center. My question is why the pyramid/tetra transition...the nodes end up in pretty much the same distance from the wall as if the whole thing was just hexas. Is there a CFD solving advantange for ANSA to do this? It's certainly not helping with resolving the boundary layer, since the first nodes off the wall of each pyramid is way too far away anyway. (I would never really expect good wall results doing this; I would in all practicality use prism layers...but still...the pyramid/tet transition would still exist).

Any clue? or is that just the way it is? Also, I tried to be clear with my question but I understand it's confusing, so let me know if you need any clarification!

Thanks in advance!
eishinsnsayshin is offline   Reply With Quote

Old   October 25, 2012, 04:02
Default
  #2
Senior Member
 
Vangelis Skaperdas
Join Date: Mar 2009
Location: Thessaloniki, Greece
Posts: 165
Rep Power: 9
vangelis is on a distinguished road
Hi there,

HexaInterior and HexaPoly algorithms are meant to generate hexas inside the main core of the volume for complex geometries where having pure hexa mesh is not possible. Therefore there is this transition zone with pyramids and tetras, so that the mesh can adjust to the complex surface of the model. Prior to using these algorithm one probably also generates boundary layers from the surfaces. You can refer to tutorial meshing for external aero.

If you have a simple geometry, like a square box, meshed with map quads then it is better to use VOLUMEs>MAP
You select one side and confirm, the opposite side and confirm and then the remaining round sides and confirm.
ANSA will generate a pure hexa mesh in this case.

Another option to generate pure hexa meshes is the HexaBlock menu of ANSA, please refer to respective tutorial of ANSA.

Hope this helps
Vangelis
vangelis 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
No layers in a small gap bobburnquist OpenFOAM Native Meshers: snappyHexMesh and Others 6 August 26, 2015 09:38
Moving mesh Niklas Wikstrom (Wikstrom) OpenFOAM Running, Solving & CFD 122 June 15, 2014 06:20
2D Mesh Generation Tutorial for GMSH aeroslacker Open Source Meshers: Gmsh, Netgen, CGNS, ... 12 January 19, 2012 04:52
ICEM CFD:need help on 2D Tetra Mesh generation Farid CFX 0 October 18, 2007 18:38
3-d elliptic generation mesh Gang Sun Main CFD Forum 5 September 16, 1998 00:24


All times are GMT -4. The time now is 05:06.