Help with periodic boundaries
 

Hello there,

I am trying to define periodic boundaries for the structured mesh of a centrifugal compressor. To do so I created the geometric camber line of the impeller and diffuser blades. I rotated the curves so that they are in the middle of the passage and I extruded the lines in the direction of rotation. Finally I defined the curves of intersection between the newly created surfaces and the hub/shroud surfaces. That was a quite laborious work! Does Icem have any automatic feature to define periodic boundaries? Is there any shortcut?

I went in the Mesh>Global Mesh Parameters>Set up periodicity
I defined a periodicity based on the number of blades of the impeller. I defined periodic vertices (and therefore surfaces). Unfortunately, like for almost 99% of turbomachinery, the periodicity of the diffuser is different from that of the impeller. I could not create the grid and I feel like I have been wasting over 1 week of work. Is there any way I can use multiple periodicity in ICEM?

Please, help :). Thank you very much!

actually I posted a similar thread few days ago, but since I did not get any answer at all I felt like I did not explain the problem clearly.

Nope, no multiple periodicity... You must mesh the diffuser and impeller separately...

As for making the periodic geometry, ICEM CFD is focused on meshing. There are some geometry tools as a convenience and I know that some people have done amazing things with them, but I would recommend complex geometry manipulations be done with a CAD tool, and then import the CAD model with one of our direct CAD interfaces...

Thank you very much for the answer! Actually, :D It is exactly what I am doing. I created 4 separate grids. 1 for the impeller, 1 for the diffuser/return channel and 2 for the labyrinth seals.
I am using mixing planes in Fluent in between the different periodic zones.

It is even better, so that I can work with smaller grinds (faster graphic), and I do not need to keep the number of nodes constant in between the different parts (huge advantage). I am almost glad Icem did not have multiple periodicity.

Thanks a lot... the problem is solved. Now I am dealing with Fluent, and I am trying to understand if I can use the mixing plane at the trailing edge of the blade... but I guess that I should ask it in the Fluent forum :p.