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-   -   CFX and ICEM CFD - structured meshes (http://www.cfd-online.com/Forums/cfx/64213-cfx-icem-cfd-structured-meshes.html)

realanony87 May 3, 2009 17:59

CFX and ICEM CFD - structured meshes
 
I have made a structured mesh in ICEM CFD, and the usual way I transfer it to CFX is to first convert the mesh to the unstructured format (*.uns) and open it in CFX.
Is there a way to make CFX use of the fact that the grid is a multiblock structured grid, so as to have a faster processing time ?

ghorrocks May 3, 2009 18:41

Hi,

No. CFX is a fully unstructured solver so structured meshes are treated the same as unstructured meshes. However, there are still advantages in using structured meshes in CFX - in some cases the mesh quality of a structured mesh is better and that leads to better accuracy and convergence (this is especially important for things like boundary layers, free surface and surface tension modelling); and secondly a hex mesh uses less memory than a tet mesh of equivalent resolution.

Glenn Horrocks

Stein May 9, 2009 08:32

Puzzled
 
Quote:

Originally Posted by ghorrocks (Post 215012)
Hi,

No. CFX is a fully unstructured solver so structured meshes are treated the same as unstructured meshes. However, there are still advantages in using structured meshes in CFX - in some cases the mesh quality of a structured mesh is better and that leads to better accuracy and convergence (this is especially important for things like boundary layers, free surface and surface tension modelling); and secondly a hex mesh uses less memory than a tet mesh of equivalent resolution.

Glenn Horrocks

I feel puzzled by ur answer.
Firstly,you said CFX is a fully unstructured solver,does that mean CFX cant treat structured mesh?
Secondly ,but u still said there are still advantages in using structured meshes in CFX .
So ,it seems like your answer is in conflict.

ghorrocks May 10, 2009 21:53

Hi,

I mean CFX internally handles structured and unstructured meshes the same. For instance a node in a structured mesh can be referred to by its IJK coordinates. CFX does not use this and uses the unstructured approach of an element connectivity matrix which works for both structured and unstructured meshes.

My second point is that if your geometry is simple enough such that a high quality structured mesh works in your geometry then you will get better mesh quality with this type of mesh rather than an unstructured mesh.

Glenn Horrocks

Stein May 12, 2009 06:22

Well,I get it now!
There is another question.
In ICEM,how can structured mesh be constructed?
As we know,meshing by blocking approach in ICEM finally should be converted to unstructed, and then output to CFX.Howerver, other meshing approaches such as Octree tetra in ICEM are used to construct unstruceted mesh.So ,does that means ICEM cant construct structed mesh?
Secondly ,by blocking approach there is another method to convert "premesh",namely "multi-block".I dont know what this method used for.When i convert premesh to multiblock and output to CFX,error was presented all the time.Does that means CFX cant treat muti-block mesh.

ghorrocks May 12, 2009 18:45

Hi,

To generate structured meshes in ICEM you need ICEM-hexa. This is an additional license option, contact your CFX vendor. When you have the license and done some tutorials in hexa things will be clearer.

CFX can handle a multi-block mesh.

Stein May 14, 2009 11:18

My comprehesion is that ICEM-HEXA is just the blocking mehod in ICEM,isn't it?
By blocking ,hexa grid can be generated,but usually the premesh needs to be converted to unstructured,which I think is unstructured mesh generated at last.

ghorrocks May 14, 2009 18:22

Hi,

No, ICEM can generate fully structured meshes. So for block structured solvers ICEM can generate meshes. It is just that when you read a structured mesh into CFX it will get treated the same as an unstructured mesh.

Glenn Horrocks

Stein May 14, 2009 21:05

Hi
About ur answer,is there any documentation or some threads containing the detailed information on how CFX treat its mesh,namely some theory about this.
Unfortunately, I cant find any specification about this in CFX's help documentation
By the way,thank u for ur help very much

ghorrocks May 14, 2009 21:10

Hi,

It is all in the theory manual. There are also a few threads on it on this forum, use a search to find them.

Glenn Horrocks

suihenry May 15, 2009 05:17

Quote:

Originally Posted by realanony87 (Post 215011)
I have made a structured mesh in ICEM CFD, and the usual way I transfer it to CFX is to first convert the mesh to the unstructured format (*.uns) and open it in CFX.
Is there a way to make CFX use of the fact that the grid is a multiblock structured grid, so as to have a faster processing time ?

Hi,
Usually, in ICEMCFD, there are output option which can save the structured mesh as .msh file. This file can be easily and directly opened in CFX.
What you need to do is to set a product option. in ICEMCFD, click the "settings" option in main menu, then choose the "Product" option, then choose the " ANSYS ICEM CFD-ANSYS Solvers Version" option. then click OK, then exist the software. When you open the ICEM CFD 11.0 again, you can click the "output" in the toolbox menu, there are four option which can save mesh as different types corresponding ANSYS software(like CFX, ANSYS, ANSYSWORKBENCH, Fluent and so on).


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