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Electrical Machinery Windage Loss Reduction

As surface speeds of electrical machinery increase to meet ever more demanding application requirements, windage power losses due to shearing of air (or other process fluid) between the rotor and stator take on an increasingly significant role. Historically, these losses have not received a great deal of research attention. Common approaches include making the rotor and stator surfaces as smooth as possible, keeping the rotor-stator gap as large as practical without compromising electrical efficiency, and simply accepting whatever losses are present.

Xdot Engineering and Analysis, along with Computer Aided Engineering Associates, recently completed a two year Phase II SBIR effort funded by the US Air Force to look at these losses in more detail. This work included extensive Computational Fluid Dynamics (CFD) analysis and experiments in a new high speed windage power loss test rig. The outcomes of this effort included:

  • Development of an easy to use ANSYS/CFX windage power loss modeling and analysis module.
  • Generation of a new database of analytically predicted rotor power losses for high-speed electrical machinery.
  • Development and commissioning of a windage loss test rig capable of accurately measuring rotor power loss at speeds of up to 60,000 rpm.
  • Generation of a new database of experimentally measured rotor power loss at relevant surface speeds and test article scale for 50 kW to 200 kW, high speed electrical machinery.
  • Identification of several strategies which are predicted to reduce the windage loses by  as much as 30 percent in specific cases for high surface speed applications.

These approaches also appear to have promise for higher viscosity gases and fluids at lower surface speeds.