Direct-drive electromachines that are designed to operate at higher rotating speeds will have a windage drag that is a more significant loss factor; this loss will require greater attention in the initial machine design. Switched-reluctance machines with poled rotors can further increase windage by fluid pumping and mixing between the rotor poles. Reliable windage data for highspeed poled rotors was unavailable, so an experimental study was initiated to determine the total air friction power loss and the contributing factors to this loss. The first rotor test was with concentric cylinders to establish a valid viscous film theory. The parametric analysis then proceeded with a matrix of tests for various rotor, stator, and air gap geometries. Later tests with rotor end “shrouds” then demonstrated reduced windage loss by reducing the induced airflow and mixing in the rotor pole gaps.

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