Impact of Hairpin End Winding Geometry on Spray Cooling Performance

This paper examines how end winding geometry impacts the convective Heat Transfer Coefficient (HTC) of a 150 kW, 72-slot, 8-layer hairpin stator end winding cooled by a single-phase oil spray system. Fluid flow in the end winding region is analyzed using the Moving Particle Semi-Implicit (MPS) Method. A parametric geometry model creates three different hairpin crown geometries to investigate effects of radial spacing and axial extrusion height on cooling performance, specifically HTC, wettability, and temperature distribution. Findings indicate that increasing radial spacing between layers results in a small 1.1% surface area increase per layer but can significantly enhance wet-tability and temperature uniformity by limiting the temperature gradient across the winding to 25 °C. In contrast, axial protrusion results in larger end windings with up to 14.0% surface area increase per layer, but HTC and temperature distribution results indicate reduced wettability and temperature uniformity. These findings highlight trade-offs between end winding geometry and fluid distribution, offering design guidance for optimizing thermal management in oil-cooled traction motor stators.