A CFD-Based Numerical Evaluation, Assessment and Optimization of Conjugate Heat Transfer for Aerodynamic Cooling of a Wheel-Hub-Motors in Micro-Mobility Vehicles

Micro-mobility vehicles such as electric scooters and bikes are increasingly used for urban transportation; their designs usually trade off performance and range. Addressing thermal and cooling issues in such vehicles could enhance performance, reliability, life, and range. Limited packaging space within the wheels precludes the use of complex cooling systems that would also increase the cost and complexity of these mass-produced wheel motors. The present study begins by evaluating the external aerodynamics of the scooter to characterise the airflow conditions near the rotating wheel; then, a steady-state conjugate heat transfer model of a commercially available wheel hub motor (500W) is created using commercial computational fluid dynamics (CFD) software, StarCCM+. The CAD model of the motor used for this analysis has an external rotor permanent magnet (PM) brushless DC topology. Both internal and external fluid domains are considered to evaluate the combined flow dynamics and conjugate heat transfer from the windings (heat source) to the ambient air. At the maximum speed (482rpm) of the motor, for a total power loss of 180W (η=64%), a maximum temperature of 295°C is observed in the windings. Evaluating the thermal path shows that approximately 58.1% of the total heat generated in the winding is dissipated radially via convection through the air gap, and only 3.66% through the shaft via conduction. The thermal resistance for the shaft is in the range of 22-60 K/W and the rotor components is in the range of 0-2 K/W for the operational speed range of 0-1000rpm. Taguchi's Design of Experiment (DOE) with Design manager study has been conducted to optimize the performance of design parameters (Fins and air-vents/holes) in cooling the motor. Air vents and external fins on rotor-lid (rotor cover) has a greater effect on cooling the motor than other design parameters.