The Effect of Rotor Notches on Air Gap Heat Transfer Coefficient and Electromagnetic Performance in a Traction Permanent Magnet Synchronous Motor

This study investigates the impact of various notch geometries, specifically on the outer surface of the rotor of a permanent magnet synchronous motor, on the thermal and electromagnetic (EM) performance. Typical motor cooling methods, such as water jackets or oil spray/impingement, usually target the stator and/or end windings, relying on heat transfer through the airgap to cool the rotor, even though air acts as an insulator. Rotor notches are often used to reduce cogging torque and torque ripple by improving the quality of air gap flux density distribution, leading to a significant increase in motor efficiency and overall performance. The effect of rotor notches on EM performance is well understood, but its impact on the thermal management of the motor, particularly the heat transfer coefficient (HTC) in the airgap, remains unexplored. While existing experimental and analytical work has focused on heat transfer in the airgap for smooth stator and rotor or a slotted stator with a smooth rotor, no studies have examined the effects in machines with a notched rotor. The proposed work uses Computational Fluid Dynamics to model fluid and thermal behavior and finite element analysis to determine EM performance for different notch geometries. By investigating the notch geometry with a commercially available machine as a baseline, the study aims to enhance the HTC in the airgap, improving rotor cooling, without compromising EM performance. The results of this study provide valuable insights for developing advanced rotor designs that achieve excellent thermal and EM performance for high power density applications.