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Comprehension and Estimation of Windage Losses in Rotor Slotted Air Gaps of Electrical Machines using CFD-LES methods

This paper presents the use of Computational Fluid Dynamics (CFD) simulations for the study of airflows in very narrow slotted air gaps of high-speed electrical machines. For this purpose, the wall shear stress on the rotor surface, the rotor skin friction coefficient as well as the windage losses are evaluated numerically. We propose to decompose the rotor in five elementary surfaces and evaluate their respective contributions. This approach will allow to apply the method to various geometries of slotted rotors. CFD results are used to analyze accurately the airflows and we propose a method based on these numerical results, which allows the determination of the classic rotor skin friction coefficient. Results are compared to classic correlations.