Heat Transfer Analysis of an Electric Motor Cooled by a Large Number of Oil Sprays Using Computational Fluid Dynamics

This paper reports on an analytical study of the heat transfer and fluid flow in an electric vehicle e-Motor cooled by twenty five sprays/jets of oil. A three-dimensional, quasi-steady state, multi-phase, computational fluid dynamics (CFD) and conjugate heat transfer (CHT) model was created using a commercial CFD software. The transport equations of mass, momentum, energy and volume fraction were solved together with models for turbulence and wall treatment. An explicit formulation of the volume of fluid (VOF) technique was used to simulate the sprays, a time-implicit formulation was used for the flow-field and three dimensional conduction heat transfer with non-isotropic thermal conductivities was used to simulate the heat transfer in the windings. An important challenge was to formulate an efficient solution algorithm that can rigorously comprehend twenty five sprays in order to accurately predict the temperature distributions in the windings, without thrifting physics, and within reasonable total analysis turn-around times. The latter includes both model set-up times as well as run times. User functions were coded in order to implement the efficient solution methodology. The outcome of this effort was a novel solution technique which due to its economical analysis times of the order of a week or so, can play a key role in virtually optimizing the e-Motor design, reduce dependence on costly and time consuming tests and shorten product development times. The predicted temperatures of the windings show good agreement with thermocouple measurements.