CFD Based Aerodynamics Conjugate Heat Transfer and Airgap Fluid Flow Thermal Analysis to a Wheel Hub Motor for Electric Scooters

Abstract

The geometry of commercially available wheel hub motors inherently restricts packaging space and may prevent the introduction of more sophisticated, efficient, and expensive cooling systems. Due to the limited available space in the wheels, commercial hub motors often rely on aerodynamic passive cooling. The small air-gap (0.5–1 mm) between the coils and the magnets results in heat transfer to the magnets and consequently increases their temperature. As a result, the perfeormance of the permanent magnets (PMs) will be limited and also will heavily affect their lifetime; thus, advanced cooling strategies must be introduced. In the current study, a three-dimensional (3D) thermal model was developed for a commercially available 500 W scooter hub motor under a constant heat load of 180 W using Computational Fluid Dynamics (CFD) (= 64%).The spatial distribution of the temperature for the motor parts are evaluated considering both the internal and external fluid flow dynamics. Further, analysis of airflow in the the gap is performed and the results from the CFD is compared with the published correlations. The flow in such small motor was found to be laminar with Taylor number below 40. Results also showed that enhancement of the cooling is necessary to avoid damage of the winding vernish and to reduce the magnets temperature particularly when the motor works at high torque with low efficiency.