CFD Online Logo CFD Online URL
Home > Forums > Software User Forums > ANSYS > ANSYS Meshing & Geometry

[Other] structured or unstructured?

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

Like Tree4Likes
  • 3 Post By PSYMN
  • 1 Post By chg

LinkBack Thread Tools Display Modes
Old   March 13, 2011, 17:00
Default structured or unstructured?
Senior Member
morteza08's Avatar
Join Date: May 2010
Location: Iran,Islamic Republic of
Posts: 161
Rep Power: 9
morteza08 is on a distinguished road
hi dear all
a question?
what is the different between structured and unstructured mesh in generating good results in fluent?
for example? for a 3d impingement jet, what is the different between these two types? i want to obtain yplus=1 and good distribution for nusselt number
morteza08 is offline   Reply With Quote

Old   March 14, 2011, 04:30
Senior Member
Join Date: Jun 2009
Posts: 100
Rep Power: 10
alastormoody11 is on a distinguished road

the idea is that using a structured mesh you can have faces normal to the direction of flow or aligned to the direction of flow thereby reducing the error during flux calculations.

In unstructured mesh you have no control over the orientation of faces thereby leading to an increase in the spatial discretization error.
alastormoody11 is offline   Reply With Quote

Old   March 14, 2011, 16:30
Default Hexa can be Unstructured...
Retired from CFD Online
PSYMN's Avatar
Simon Pereira
Join Date: Mar 2009
Location: Ann Arbor, MI
Posts: 2,665
Blog Entries: 1
Rep Power: 39
PSYMN has a spectacular aura aboutPSYMN has a spectacular aura about
I agree that alastormoody already answered your question. He is correct in that hexas aligned with the walls will better capture your fluxes (the first principles of the code are formulated with these assumptions), hexas also fill your volumes more efficiently, can be biased to better capture boundary physics, etc.

but it is not quite right to think of unstructured as tetra and structured as hexa... Maybe this is just a semantics thing, but I think it helps if we all speak the same language.

"structured" is more about how the data is stored. (domains with ijk instead of nodes with XYZ). It can only be done with Hexa and results in conveniently small files that solvers can turn into matrices very easily. Many in house solvers and older versions of comercial solvers are "structured" solvers that require a structured mesh. Without getting too technical, these solvers can use the implied information in the grid to take shortcuts.

More modern commercial solvers tend to be unstructured. Unstructured mesh stores the data for all the elements and nodes individually. Each element number is cross referenced with an element type and the node numbers. Each node number gives a physical (XYZ) location. You can't tell from any particular node or element number which elements are surrounding it or where it is in the big scheme of things, so the solver must do more work to figure out the matrix.

ICEM CFD hexa can output hexa mesh as structured or unstructured mesh (for unstructured solvers like Fluent). Older versions of Fluent (such as V4) actually needed "structured" mesh.
PSYMN is offline   Reply With Quote

Old   March 15, 2011, 12:06
New Member
Join Date: Mar 2011
Posts: 2
Rep Power: 0
enviro is on a distinguished road
Hi dear all,

i have another question referring to hexa/tetra-meshing.

You mentioned that hexa-mesh...
>is better to capture your fluxes
>fill your volumes more efficiently
>is better capture boundary physics

Is there any literature you could suggest to get to know the reasons of these points?
Or maybe a study about the difference of tetra/hexa-meshing?

I often read sentences like "hexa-meshing is more sufficient for CFD, than tetra, because it captures the physics in a better way" but i do miss the references for it.

Would be great if you could help me!

kind regards
enviro is offline   Reply With Quote

Old   December 12, 2011, 04:57
New Member
Join Date: Apr 2011
Posts: 11
Rep Power: 8
chg is on a distinguished road
Here is one paper I found: Comparison of Hexa-Structured and Hybrid-Unstructured Meshing Approaches for Numerical Prediction of the Flow Around Marine Propellers
shereez234 likes this.
chg is offline   Reply With Quote


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
OpenFOAM - structured or unstructured Grids ? thomasduerr OpenFOAM Meshing & Mesh Conversion 20 March 13, 2017 07:07
Structured to Unstructured grid Sen Main CFD Forum 2 March 2, 2011 12:33
Structured and Unstructured mesh Jingwei FLUENT 0 March 2, 2009 22:29
combining structured and unstructured grids Shane FLUENT 2 January 23, 2007 21:57
Structured and Unstructured grids Samir FLUENT 0 February 5, 2005 22:21

All times are GMT -4. The time now is 07:26.