CFD Online Discussion Forums

CFD Online Discussion Forums (http://www.cfd-online.com/Forums/)
-   ANSYS Meshing & Geometry (http://www.cfd-online.com/Forums/ansys-meshing/)
-   -   [ICEM] Setting Periodic Boundary Conditions (http://www.cfd-online.com/Forums/ansys-meshing/96630-setting-periodic-boundary-conditions.html)

Arjun87 January 27, 2012 12:04

Setting Periodic Boundary Conditions
 
1 Attachment(s)
Hi I am pretty new to ICEM CFD and need you help. I would like to set periodic boundaries on the sides of this simple geometry.

[IMG]file:///tmp/moz-screenshot.png[/IMG]
Could anyone tell me how to do it? I tried the following.

Went into Mesh --> Global Mesh Setup -----> Global Mesh Parameters ----> Setup periodicity ----------> Rotational Periodicity -------> Rotational Axis ---- User Defined --->

Base : 0 0 0 ( I did not understand its physical meaning so set to origin)
Axis: 1 0 0 (I needed the object to be rotated about x-axis)
Angle: 90 ( as the sector makes 90 degrees)

Is this the right way to do ? I also tried the edit block periodic vertices but could not really understand how to use it. SO could anyone tell me how to set periodic faces. Thanks

Far January 27, 2012 16:10

Check this

Far January 29, 2012 23:37

This is the what I found from the ICEM 10 tutorial guide.
3.15. Periodicity
Periodic definition may be applied to the model in Hexa. The Periodic nodes function, which is found under Blocking > Periodic nodes, plays a key role in properly analyzing rotating machinery applications, for example.
Typically, the user will model only a section of the rotating machinery, as well as implement symmetry, in order to minimize the model size. By specifying a periodic relationship between the inflow and outflow boundaries, the particular specification may be applied to the model -- flow characteristics entering a boundary must be identical to the flow characteristics leaving a boundary.
3.15.1. Applying the Periodic Relationship
The periodic relationship is applied to block faces and ensures that a node on the first boundary have two identical coordinates to the corresponding node on the second boundary. The user is prompted to select corresponding vertices on the two faces in sequence. When all vertices on both flow boundaries have been selected, a full periodic relationship between the boundaries has been generated.

I am also confused in term Base.

Arjun87 January 30, 2012 08:39

1 Attachment(s)
Dear Far, thanks a lot for both of your kind replies. I still could not figure out the order to set the periodicity. I have attached this very basic setup of the case. I have already set the periodic condition in the global mesh set up. Then I went into the vertex periodicity in the blocking. I also activated the solid blocking and show periodic face in the blocking section of the model tree to understand. But after every time I finishing selecting the vertices, I get the periodic faces weirdly highlighted. I tried seclecting the vertices in different ways but still wrong periodic faces. Can you please tell me the sequence to set up the periodic boundary condition. Could you please let me know how to do this periodicity?

Arjun87 January 30, 2012 08:49

Far ! I have found the answer. I went into vector defined in Global parameters and then selected two points in the axis of rotation. Then I went into vertices association and selected one node on one periodic face and corresponding node in the other periodic face ... bingo ! I got the periodic condition on the periodic faces. Thanks :)

Far January 30, 2012 10:47

Hi Arjun,

I am unable to understand that what is the purpose of all this in ICEM. If you just export the mesh with periodic boundaries as wall, you can still make them periodic in Fluent.

Far January 30, 2012 11:06

Quote:

Far ! I have found the answer. I went into vector defined in Global parameters and then selected two points in the axis of rotation. Then I went into vertices association and selected one node on one periodic face and corresponding node in the other periodic face ... bingo ! I got the periodic condition on the periodic faces. Thanks
I dont think so you could get periodicity in this way!!!!

Arjun87 January 30, 2012 11:59

Dear Far, Do you know the correct way to do it ? I am not sure whether its the right way but I got periodic condition. It will be helpful if you could say.

And answering to your question, periodic conditions ensures that there is a one to one r-theta match in the periodic nodes. Not all solvers unlike Fluent are capable of dealing with periodic meshes where a strict one to one matching does not occur. Hence the strict periodicity needs to be ensured in meshing before sending into solver.

Far January 30, 2012 12:50

What I want to say is that, any software should be intelligent enough to understand the basic requirements.
For example

1. if you increase the sector from 90 to 120, you again need to copy the geometry to those angles and and again re-associate the edges, vertices and faces. This should be handled automatically in code.

2. Some times it is not good idea in turbo machinery to model the strict plain surface in periodic boundaries, instead they should be floated in a way to facilitate the blocking. For example some times it is better to align the blade blocking near the low periodic and some times to high periodic depending on the blade angles and curvature.

3. Once you have defined the two surfaces as periodic then they should show periodic condition in the boundary condition panel (in output tab), instead asking user to define it.

With the help of GGI (general grid interfaces), you dont even need the periodicity in mesh at all. You can make two dissimilar face meshes periodic by use of GGI method. Available in both Fluent and CFX.

Far January 30, 2012 12:55

Quote:

Dear Far, Do you know the correct way to do it ? I am not sure whether its the right way but I got periodic condition. It will be helpful if you could say.
I also use similar method, I go to global mesh settings and set the required angle and axis. Since currently I am working on bladegen and get the turbine or compressor file from there, I normally find that these conditions are pre defined.
But I have no idea about the base point that how is defined and what is physical significance.
Then I go to Block---> edit block ---> Periodic vertices and make the vertices periodic and when I display the vertex with periodicity on, I can see the red arrow pointing to each other.

Far February 6, 2012 13:58

I guess that base point is important in 2-D vertical wind turbine periodic setup, where you pivot the whole mesh.
Vertical wind turbine

masoud_k71 April 14, 2015 03:05

how to make periodic boundary condition in a cube
 
Dear friends
I want to make periodic bondary conditions in the left and right side of a cube,and I dont know how can I do that.
I wanna you to help me,I konw it is very simple but I am amateur in gambit :(

FJSJ April 14, 2015 05:12

Hi Masoud! Just try to check out the second reply on this thread posted by FAR. There, you can find explanation and videos about how to do this in ICEM CFD! Hope it helps :)


All times are GMT -4. The time now is 18:38.