Numerical Study of Convective Heat Transfer in the End Regions of a Totally Enclosed Permanent Magnet Synchronous Machine

This paper proposes a numerical approach for the accurate estimation of convective heat transfer coefficients in the end region of an integrated starter generator (ISG) used in a mild-hybrid vehicle. A simplified numerical model based on CFD methods is developed to provide a qualitative understanding of the mechanism of convective heat transfer over a large operation range. The effect of the rotation speed on the variation of the convective heat transfer coefficients inside the end region is thoroughly investigated. Heat flux paths are also identified for the entire operation range. CFD calculation results are used to provide an enhancement to Schubert's correlation for the different surfaces delimiting the end region of the ISG. Subsequently, general correlations are defined using averaged Nusselt numbers as a function of Reynolds numbers. Then, a detailed lumped thermal network is developed which estimates correctly the temperature distribution in different areas of the electrical machine. The obtained numerical data are validated using local temperature measurements.