Windage Losses Calculation and Performance Estimation for Wet Airgap PM Machines

With an increased need for high power density machines, especially for the motor-driven pump application, flooded airgap offers a good solution. However, the main disadvantage related to this configuration is the high windage loss generated at the air-gap due to the viscosity of the fluid, which can result in very high temperatures on the rotor surface and drag forces on the rotating components. This required an accurate prediction of windage losses to estimate the reduction in mechanical output torque and to evaluate exactly the heat generated on the rotor surface, which can cause a series of problems like the demagnetization of the magnet in PM machines. Also to accurately estimate the machine's performance. Therefore, this paper investigates the impact of machine design parameters on the windage losses generated inside the airgap of high speed machines, and the resulting variations in the machine efficiency are presented and described. Both theoretical and finite element modeling have been used in the analysis.