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-   -   Creating periodic or cyclic mesh (http://www.cfd-online.com/Forums/star-cd/82988-creating-periodic-cyclic-mesh.html)

cfdengineer December 10, 2010 12:05

Creating periodic or cyclic mesh
 
I am using pro-star version 4.12. I have a simple combustor annulus sector where I want my sides to be cyclic. I have searched for an option in pro-surf to make those sides cyclic but to to avail. Can pro-surf create a cyclic mesh? or do I create the surface mesh in pro-surf and there is an option in pro-am where it will make the mesh cyclic? After I surface mesh this in pro-surf I will be going into pro-am where I will be putting an extrusion layer.

Pauli December 10, 2010 12:20

Prosurf is basically just a surface mesher with surface repair and grouping capabilities. The cylic symmetry is specified using Prostar boundary conditions. In the Locate Boundaries panel, make each side a separate cyclic boundary region. Then use the Cyclics tab to match them together.

You should end up with somethign like this:
rdef,1,cyclic
1,all,regular,integral
rdef,2,cyclic
1,all,regular,integral
cymatch,1,2,0,0,0,0.0001

cfdengineer December 10, 2010 15:54

I plan on running this in CFX, so there is no way to make the mesh itself truly periodic? From what you said it looks like it is matching each side kind of like a interface bc? Am I interpreting your comment corrrectly? Or does what you say actually rearrange the nodes so that they are truly periodic?

Pauli December 10, 2010 17:23

Assume your sector encompases 1/4 the annulus (a 45 degree sector). The method I outlined will "couple" the faces on either end of the 45 degree sector. In other words, what comes out the face at 0 degrees will go into the face at 45 degrees.

Do you want to copy/rotate the mesh to make a full 360 degree annulus? If so, inside prostar you use the cgen command with the vgen option with a cylindrical coordinate system set as the currently active csys. Sounds like this might be what you want. I don't remember for certain but you might then need to vmerge the nodes at the interfaces. A qhid plot will show you.

cfdengineer December 13, 2010 15:20

Pauli, when you say "couple" I am assuming you mean a boundary coupling, like an interface? and not a true node-to-node coupling based on a theta angle and axis rotation. Basically if I have a 30 degree sector I want all say 100 nodes on face x to match all 100 nodes on face y rotated 30 degrees. Basically, I just don't want to use a interface in CFX. I have done this in ICEM where you have the geometry present and you define your sector angle and axis and then ICEM automatically creates the periodic, but since the group I work for uses Star for its meshing I am trying to make this work. Thanks.

Pauli December 14, 2010 12:53

The procedure I outlined in my 12/10 post is the Prostar/STAR procedure for running a 30 degree sector axi-symmetric model with cyclic symmetery. So yes, this boundary coupling is essentialy an interface which imposes cyclic symmetry.

Sounds like your ICEM experience does this at the geometry level. In Prostar, building the coupling/interface happens at the mesh level. The cyclic matching can handle node-to-node "matched" meshes or interpolate between arbitrarily different meshes.

If you are going to run in CFX, you need to move the mesh from Prostar to the CFX pre-processor. Does this move include boundary condition specifications? If not, you will need to figure out the equivalent CFX commands/operations. I don't see how you can get around that one.


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