Analysis of Flooded Hairpin Winding Cooling for an Automotive Axial Flux Traction Motor using Computational Fluid Dynamics

The global consensus of pursuing 'Net Zero' to tackle climate change is driving the automotive industry into electrification. Ambitious roadmaps and machine performance requirements are encouraging revolutionary technologies to be explored. Axial flux permanent magnet machines are a prime focus in the automotive industry, as they can provide the challenging power-density and cost requirements needed to compete with internal combustion engines. Flooded cooling enables high-power output without compromising on thermal feasibility. Whilst previous studies have considered this cooling topology for axial flux machines, its application for designs with distributed, hairpin windings remains an unexplored topic. This study investigates the thermal performance of flooded cooling for the hairpin endwindings of an axial flux machine. A modelling methodology for reducing the complexity of computational fluid dynamics simulations is proposed. Variations in dimensions and fluid parameters were considered in a sensitivity study to analyse their influence on cooling performance. Parameters that influenced coolant flow rate showed the highest potential for thermal improvements, whilst changes in geometric configurations enabled an improved uniformity of endwinding heat transfer. The results presented provide a guide on the key parameters for enhancing flooded hairpin endwinding cooling performance for axial flux machines.