Is it possible to nest a rotating domain inside of another rotating domains?



It`s certainly possible to have rotating domain that is completely surrounded by another rotating domain, but the rotational motion of the inner domain is not superimposed on the rotational motion of the outer domain. In the general case the inner rotation can be accounted for using the moving mesh feature while the outer rotation is accounted for using a rotating domain, in which case only a single domain in needed. The disadvantage of using a moving mesh to simulate rotating components is that the simulation is always transient and you generally need a small timestep compared to a rotating domain approach.
Another approach is to account for the inner rotation by setting a wall velocity about a local coordinate axis. However, this is only valid when the wall velocity is tangential to the local rotation axis, e.g. a cylinder rotating about its local axis; this would not work for a blade. The CFX Solver accepts the following CCL to set this type of boundary condition (CFX-Pre does not accept this CCL):

FLOW:
DOMAIN: Rotating Domain
BOUNDARY: Local Rotating Wall
Boundary Type = WALL
Frame Type = Rotating
Location = MyWall1
BOUNDARY CONDITIONS:
WALL INFLUENCE ON FLOW:
Option = No Slip
WALL VELOCITY:
Angular Velocity = 200 [radian s^-1]
Option = Rotating Wall
AXIS DEFINITION:
Option = Coordinate Axis
Rotation Axis = Coord 1.3
END
END
END
WALL ROUGHNESS:
Option = Smooth Wall
END
END
END
END
END

This CCL will rotate the wall about the z-axis of the local coordinate frame "Coord 1". The entire wall is also within a rotating domain rotating about a different axis.





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