Convective Heat Transfer Characteristics on End-Winding of Stator Immersed Oil-Cooled Electrical Machines for Aerospace Applications

The stator immersed oil cooling has emerged as a promising thermal management method for high power density electric machines applied in aerospace applications. However, due to the complex geometry of end-winding, the research on the convective heat transfer coefficient (CHTC) for the flooded stator is still at infancy. This article investigates the convective heat transfer characteristics on end-winding of stator immersed oil-cooled electrical machines by computational fluid dynamics (CFD) methods and experiments implemented on a motorette. The variation law of the CHTCs of end-winding with flow rate is thoroughly investigated. Subsequently, new dimensionless correlations are defined using Nusselt numbers as a function of Reynolds numbers, which are further applied into a detailed lumped-parameter thermal network (LPTN) for rapid evaluation of temperature distribution. Finally, the obtained simulation results are verified by local temperature measurements. The experimental results also show that the proposed stator immersed oil-cooled structure can withstand a current density of up to 30 A/mm2 with a corresponding continuous power density of 6.8 kW/kg.