Rotator/Stator geometry

Nessan

Hello there,

I am a new CFD student. I want to simulate a mixer with impeller at center of the mixing tank. I do not have any other CAD package except CFX-Build to build the geometry of the model. When I ckeck the CFX 5.6 Tutorial No.15, I can not understand why two 2D regions -- Periodic1 and Periodic2, in MixerImpeller.def, is bending rather than a plane. Can anybody tell me if I can build a plane instead of bending face for these two 2D regions.

In addition, how far from the blades should I choose as a rotating domain?

Thanks

Nessan