Mrf how to select rotational zone

Hi, when I select different diameters of the rotation domain in the square cavity, the numerical results of the obtained velocity field ( velocity on a straight line in square cavity, the rotational speed is 30rpm) are different. Do you know what the reason is? please.
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Wall-12mm: A model that represents only theshaft wall is rotating.
Fluid zone-16mm: A model in which the rotational fluid domain is surrounded by the shaft wall (12 mm) and the 16 mm diameter torus.
Fluid zone-26mm: A model in which the rotational fluid domain is surrounded by the shaft wall surface (12 mm) and the toroidal diameter of 26 mm.
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Hi @lilyhao!

Could you provide us with your simulation in form of a link? Could not find it in your Dashboard - thanks a lot!

Jousef