Novel methodology for designing megawatt-scale axial flux permanent magnet motor for aerospace propulsion

Duran, Murat 2025. Novel methodology for designing megawatt-scale axial flux permanent magnet motor for aerospace propulsion. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

Decarbonising regional aviation requires propulsion systems that eliminate in-flight CO₂ emissions without compromising performance. Hydrogen-electric powertrains offer a credible pathway. However, their viability depends on propulsion motors capable of delivering megawatt-class power at high power density. Low-speed, high-torque direct-drive architectures are attractive because they remove heavy gearbox systems typically required in high-speed configurations. This thesis develops a novel, simulation-led, multidisciplinary design and verification methodology for direct-drive axial-flux permanent-magnet (AFPM) propulsion motors. The methodology is modular in structure and applied in two stages. First, a 250-kW class motor (Cardiff University AFX250) is designed using the proposed workflow and validated against the publicly available Evolito Yokeless-and-Segmented-Armature (YASA) aerospace reference motor. Second, the validated design module is scaled using the same structured methodology to define a 1400 kilowatts (kW) or 1.4 megawatts (MW) modular AFPM propulsion motor (CU-AFX1400). This two-stage progression demonstrates scalability from validated sub-MW design to MW-class propulsion. The electromagnetic workflow reduces dependence on repeated full 3D finite-element iteration while retaining early-stage predictive capability. It integrates performance sizing, magnetic-circuit modelling, phasor/reactance formulation, and analytical loss estimation within a parametric framework coupled to a multi-objective genetic algorithm. Competing objectives, power, mass, efficiency, torque ripple, and manufacturability are optimised simultaneously, enabling efficient slot/pole and geometry selection prior to high-fidelity validation. Using this methodology, the CU-AFX1400 double-rotor single-stator (TORUS), north-to-north opposing pole (NN) architecture is defined for direct-drive operation at 2,500 r/min. Three-dimensional electromagnetic FEA in ANSYS Maxwell confirms ~1.4 MW total output (two ~700 kW modules) at ~465 V phase RMS and up to ~1,000 A RMS current. However, detailed 3D conductor modelling reveals MW-scale copper-loss constraints. Skin, proximity, and fringing effects increase winding loss to ~45 kW, approximately 33% above simplified analytical estimates, reducing electromagnetic efficiency relative to initial assumptions. In contrast, core losses are ~2.16 kW, approximately 50% lower than the 3.91 kW predicted analytically. The governing feasibility constraint therefore shifts from magnetic loading to heat extraction capability. Magnetic utilisation remains acceptable using 0.15 mm non-oriented electrical steel (NO15) and high-energy magnets without significant saturation. Thermal management is consequently treated as an enabling subsystem rather than a secondary step. Candidate cooling concepts are evaluated using CFD, supported by a thermal-equivalence winding model incorporating anisotropic effective conductivities. The reduced model achieves ~8.36% temperature deviation relative to a detailed layered reference, enabling rapid yet reliable iteration. Low-temperature immersed direct-contact cooling is identified as necessary for sustained MW operation within a compact AFPM geometry. Refrigerant (R-3283) and water–ethylene glycol cooling maintain temperatures below ~60 °C at current densities up to ~30 A/mm², corresponding to convective coefficients on the order of 10⁴ W·m⁻²·K⁻¹. Under continuous high-power loading representative of critical flight segments, an efficiency of 97.0% is achieved. A complementary mechanical integration methodology evaluates structural integrity under tight airgap tolerances (<0.5 mm), ~31 kN magnetic attraction force, and 2,674 N·m torque, alongside centrifugal and fit-induced stresses. Rapid analytical screening using Roark and Lamé methods predicts <0.3 mm airgap-relevant deflections, validated by 3D structural FEA. Peak stress reaches ~260 MPa, corresponding to a factor of safety of ~2.2 relative to 7075-T6 aluminium. Rotor-dynamic analysis using Dunkerley/Rayleigh methods yields a critical speed of ~10,536 r/min, well separated from the 2,500 r/min operating speed. Although mechanically safe, solid structural components degrade the power-density target by 67.73%. Lattice conversion of eligible components achieves ~76–78% mass reduction for convertible parts, corresponding to ~33% total motor weight saving while maintaining a factor of safety (FOS) ~2. Governing constraints remain at the drive-end shaft under conservative loading, requiring hybrid skin– lattice reinforcement and manufacturing-led verification. An FMEA framework translates these findings into a structured build-and-validation route prioritising alignment, bearing preload, bonded-interface integrity, shrink-fit control, and coolant sealing. Overall, this thesis delivers a scalable, modular multiphysics methodology that links early electromagnetic design decisions to high-fidelity electromagnetic, thermal, and structural validation. The two-stage application 250 kW validation against commercially available motor Evolito YASA followed by scaling to a 1400 kW modular propulsion architecture, demonstrates both predictive robustness and scalability. The results confirm the feasibility of direct-drive MW-class AFPM propulsion achieving 97.0% efficiency and ~10.0 kW/kg power density when electromagnetic realism, low-temperature direct-contact cooling, and structural optimisation are treated as a tightly coupled design problem.

Item Type:	Thesis (PhD)
Date Type:	Completion
Status:	Unpublished
Schools:	Schools > Engineering
Uncontrolled Keywords:	1. Axial Flux Permanent Magnet Motor 2. High power density 3. Megawatt Power 4. Advanced Cooling 5. Light weight 6. Direct Drive
Funders:	KESS 2
Date of First Compliant Deposit:	1 April 2026
Last Modified:	10 Apr 2026 08:19
URI:	https://orca.cardiff.ac.uk/id/eprint/186130

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