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Mitpostdoc March 22, 2011 15:55

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!

Mitpostdoc March 22, 2011 15:56

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.

PSYMN March 24, 2011 17:40

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...

Mitpostdoc March 24, 2011 17:57

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.

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