Identifying the heat transfer coefficients on the end-windings of an electrical machine by measurements and simulations

Prediction of the thermal behaviour of an electrical machine in the design process depends basically on the used boundary conditions. The convective heat transfer coefficient represents one possible boundary condition. Due to the complicated shape of the end-windings, an analytical derivation of the heat transfer coefficient is not feasible and has to be identified empirically by using thermopiles as heat flux sensors placed at certain positions on the end-windings. This article presents the results of measured values of the heat transfer on the end-windings of an electrical machine. The gained coefficients are shown in contrast to the results obtained by numerical simulations using commercial software for computational fluid dynamics. The simulation results are discussed according to the validity of the gained heat transfer coefficient. The configuration of the simulation has been tested on a cylindrical shape in a cross flow.