Hi, at the beginning, I thank to the ones intending to help. My problem is about a part surrounding the impeller of a centrifugal pump. This part is representing the the gaps, radial and axial, around the impeller. Should I take this part as rotating or stationary? And, should I use counter rotating wall argument anywhere in this part? Best regards.

If you can put this part together with the impeller, then you should set it as counter rotating wall.

If this part is not axisymmetric, then it is better in stationary domain.

First of all, thank for your help. I can put the part togather with the impeller, but does that make sense due to reason that these gaps are about 1.5 mm which makes it a big part. Hence, may considering this part as rotating and using counter wall argument give a bad result?

Think it from physics. What does it look like when you stand on the impeller? Different frame is just to give the domain a reference.

Can you please explain your idea in a more detailed way? It is not easy to comprehend.. Thanks..

Since no one has better understanding of your case than you, my point is to define the case (everything including BCs) according to physics. CFD is only a tool, understanding the physics of your case is the first thing.

Interestingly, I am gonna do a similar case like yours using counter rotating wall. You think 1.5mm is big? What's the size of your impeller? And did you get any results yet? Thanks.

1.5mm is so big for my impeller that has about 50 mm diameter. I tried a lot of simulations with lots of probabilities. The best results came out from the one I described gaps as rotating and the outer wall of these gaps as counter rotating. But again, I am telling you that even my best results were having big problems. I suppose these helps you, if you discover anything let me know, take care.

Thank you for the information. My impeller is a little bit of bigger than yours. But my simulation includes a diffuser. Since the steady results are not accurate enough I am gonna try transient flow.