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If you want a separate zone (finite thickness) then use porous media, for a perforated plate (like a flap or the old air brakes on dive bombers) then porous jump may be more suitable.
To create separate zones in split the volume (or surface), then put the two bodies into a single part. Label the main region as "fluid" and the other region as "fluid-porous": "fred" and "ginger" also work as labels but aren't as useful.....
Which bit is rotating and in what direction?