URANS Modeling of Effects of Rotation on Flow Distribution and Heat Transfer in an Electric Motor

Abstract

Traction motors are electric motors used in vehicle propulsion. In this study, an externally cooled 3-phase AC induction motor which has cooling tubes drilled axially throughout the length of the rotor and stator, is analyzed for thermal performance. The cooling air is supplied by a centrifugal blower connected to the inlet plenum of the motor. Unlike in static condition, the relative distribution of air in the rotor and the stator tubes is not uniform and varies due to the rotation of rotor. It has been shown in previous studies that due to rotor’s rotation, the resistance of the flow path through the rotor tubes increases compared to the static condition. This results in reduction of flow through the rotor tubes. Generally, the steady state MRF (Multiple Reference Frame) approach is used to model the rotational effect. While this approach works in the initial design phase, Unsteady sliding mesh approach is suggested for design validation. It was found that at 3000 RPM, the mass flow rate in the rotor predicted by the Sliding mesh model could be as much as 16% lower than that predicted by the MRF model. To assess its impact on thermal performance, steady state conjugate heat transfer analysis was performed. It was found that the rotor temperatures could be up to 8.6-degree C higher based on the mass flow predictions by sliding mesh approach compared to the MRF approach.