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meshing axisymmetric problems with irregular boundaries

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Old   July 14, 2010, 14:12
Default meshing axisymmetric problems with irregular boundaries
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Mirko Vukovic
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Hello,

I have an axisymmetric problem wit internal flow and with an irregular outer boundary. Thus the problem is not easily handled with the blockMesh utility. Thus, I think I need to use the snappyHexMesh utility.

As I understand it, the snappyHexMesh requires an STL file. I think I can generate the STL by manually (the ascii format is described here)

Since the problem is internal, I will try to create a wedge-type background mesh, and assign wedge patches to the azimuthal faces.

Is that the right way to go about this problem?

Thank you,

Mirko
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Old   July 15, 2010, 02:13
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Elvis
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Hi,

there are many ways to generate an Stereolithography (STL)-Files. Most Cad Programs for example Salome http://www.salome-platform.org/ or freecad http://free-cad.sourceforge.net/ or Blender http://www.blender.org/ to name a few opensource programs can export to STL.

an other way is discribed here (blender->calculix->openfoam)
http://www.openfoamworkshop.org/08/p...FOAMCharts.pdf

search this forum for internal flow and snappyhexmesh (SHM) http://www.cfd-online.com/Forums/ope...rnal-flow.html

and you will find an answer how to use SHM for internal flows.
=> I believe it was s.th like you must provide s.th like "location in mesh" and this "point" has really to be inside the STL for internal flow. otherwise you would mesh outside like in a windtunnel.

before you work with "blockmesh" which should only used for simple examples try discretizer http://www.discretizer.org/ or engrid http://engits.eu/cms/index.php?id=4

Last edited by elvis; July 15, 2010 at 02:39.
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Old   July 15, 2010, 09:35
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Mirko Vukovic
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Quote:
Originally Posted by elvis View Post
Hi,

there are many ways to generate an Stereolithography (STL)-Files. Most Cad Programs for example Salome http://www.salome-platform.org/ or freecad http://free-cad.sourceforge.net/ or Blender http://www.blender.org/ to name a few opensource programs can export to STL.

an other way is discribed here (blender->calculix->openfoam)
http://www.openfoamworkshop.org/08/p...FOAMCharts.pdf

search this forum for internal flow and snappyhexmesh (SHM) http://www.cfd-online.com/Forums/ope...rnal-flow.html

and you will find an answer how to use SHM for internal flows.
=> I believe it was s.th like you must provide s.th like "location in mesh" and this "point" has really to be inside the STL for internal flow. otherwise you would mesh outside like in a windtunnel.

before you work with "blockmesh" which should only used for simple examples try discretizer http://www.discretizer.org/ or engrid http://engits.eu/cms/index.php?id=4
Thanks Elvis
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Old   July 17, 2010, 12:41
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Ola Widlund
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Hi,

Beware, snappyHexMesh will create a 3D mesh... It sounds as if you want an axisymmetric 2D mesh.

/Ola
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Old   July 19, 2010, 08:21
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Mirko Vukovic
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As I still have access to a Fluent/Gambit license (it will expire eventually), I ended up creating the wedge geometry with a hex mesh in Gambit.

I exported the mesh as a fluent file, labeling the wedge faces as symmetry.

Then I used the fluent3DtoFoam utility.

Finally, I corrected the wedge faces in the dictionaries from symmetry to wedge.

Quote:
Originally Posted by olwi View Post
Hi,

Beware, snappyHexMesh will create a 3D mesh... It sounds as if you want an axisymmetric 2D mesh.

/Ola
Regarding a snappyHexMesh into 2D mesh, I was told during a training course that one can
- set-up a wedge geometry,
- mesh it using snappyHexMesh,
- remove the 3D mesh
- extract the 2D mesh of the wedge face into the 3D domain

But I do not know the commands to accomplish that.
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Old   July 19, 2010, 08:55
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Pei-Ying Hsieh
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Hi,

This procedure is a little bit tedious, but, will get the job done:

run snappyHexMesh - make sure that you have the face as boundary patch that you want to extrude as 2D.

run extrudeMesh. Search for a file called extrudeProperties. This will give the name of the patch that you want to extrude. You will then have a 2D mesh with 1 cell thick.

rum makeAxialMesh to convert the 2D mesh into wedge.

If you already have the fluent/gamit mesh, then, you should be able to use the extrudeMesh and makeAxialMesh utilities.

Pei
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Old   July 20, 2010, 09:17
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Mirko Vukovic
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Quote:
Originally Posted by phsieh2005 View Post
Hi,

This procedure is a little bit tedious, but, will get the job done:

run snappyHexMesh - make sure that you have the face as boundary patch that you want to extrude as 2D.

run extrudeMesh. Search for a file called extrudeProperties. This will give the name of the patch that you want to extrude. You will then have a 2D mesh with 1 cell thick.

rum makeAxialMesh to convert the 2D mesh into wedge.

If you already have the fluent/gamit mesh, then, you should be able to use the extrudeMesh and makeAxialMesh utilities.

Pei
Thank you. I will take a look at extrudeMesh & makeAxialMesh

Mirko
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