[310toumad]

I'm going to be simulating a centrifugal fan in STAR-CCM+, but I have found there aren't any guidelines for best practice in terms of defining the rotating region in native CAD prior to importing into STAR. Most tutorials just show a simple squirrel-cage type blower where the rotating region is merely a cylinder that encapsulates the impeller geometry, but what if the impeller is more complex than that?

Attached is an outline of the rotating region in my CAD file shown by the black line. The OD of the rotating region sits approximately halfway between the tip of the blades and the closest point of the volute. The area I'm concerned about is circled in red where the boundary of the rotating region intersects the actual impeller itself. The reason I did not extend it any further is that it would then include a part of the housing which is stationary circled in blue. It seems tricky because the impeller and housing have such a small clearance in this location.

I assume how I have defined it is OK and that I can apply a rotation to the wall boundary of the impeller that lay outside the rotating region in STAR? Or should I be taking a different approach here?