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

Abstract : This paper proposes a numerical approach for the determination of convective heat transfer coefficients in the end region of a totally enclosed permanent magnet synchronous machine used as an integrated starter generator in a hybrid vehicle. A simplified numerical model based on CFD methods is developed to understand 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 operating range. CFD calculation results are used to provide tabulated values of the coefficients used by Schubert´s correlation for the different surfaces delimiting the end region. Subsequently, general correlations are provided using the dimensionless averaged Nusselt number as a function of the Reynolds number. All these numerical results are used to compute the corresponding thermal resistances used in the definition of a detailed thermal network model. Then, the obtained numerical data are compared to experimental temperature measurements.