Research on Influencing Factors of Airgap Windage Losses and Establishment of an Improved Windage Losses Prediction Model

Airgap windage losses can account for over 30% of all losses in high-speed permanent magnet motors (HSPMM), highlighting the necessity of conducting a detailed investigation into the factors affecting the windage losses within the airgap. In this study, the shaft-type airgap—recognized as the most representative configuration—is selected as the research subject. First, an accurate numerical method based on computational fluid dynamics (CFD) is verified to calculate windage losses. Subsequently, a quantitative analysis is performed to evaluate the effects of geometric parameters (e.g., radius ratio η and aspect ratio χ), flow characteristics (e.g., tip Reynolds numberReδ and axial Reynolds numberRea), and surface roughness (e.g., roughness heightKs) on windage losses within the airgap. The results indicate that increases in η,ReaandKslead to a higher friction coefficientCf, whereas an increase inReδ results in a reduction inCf. Moreover,Cfexhibits minimal sensitivity to variations in χ. The underlying mechanisms of these relationships are analyzed from the perspective of flow field details. Furthermore, based on the numerical results, an improved prediction model ofCfis developed. This improved model broadens the applicable flow range and demonstrates significantly enhanced accuracy compared to the original empirical models. The findings of this study provide a theoretical foundation for the structural and thermal management design of HSPMM.