Characterization of an aircraft turbo-generator design space with a shared turbine-electric rotor disk

This dissertation presents design considerations such as the impact of geometry, generator type, operating temperature, and rotational speed on the design and performance of a novel configuration of turbo-generator. The unique shared-rotor disk architecture reduces total part count by radially ”sharing” the rotor of the generator and the turbine. This allows power to be extracted, while retaining axial engine flow that can then be used to generate thrust. The architecture has several additional advantages, a reduction in weight when compared to a geared turbo-generator, the ability to quickly retrofit existing engines, and the ability to operate at a different rotational speed than the main shaft. A representative 10-kW sub-scale design point was specified and investigated, to evaluate key parameters such as the diameter ratio of turbine to overall rotor assembly, operating temperature, tip speed, and generator type. Results from detailed evaluation utilizing thermal, mechanical, and electromagnetic finite element analysis showed that the principle limiting factor was mechanical implementation of the generator structure, as opposed to the turbine structure. This observation necessitated creation of novel generator rotor configurations to handle temperature and stress induced by thermal expansion. One configuration utilizes a novel slide joint to alleviate turbine thermal expansion, whereas the other configuration utilizes turbine thermal expansion to create the required retaining sleeve interference fit. A bench test experiment involving a generator in both delta and star winding configurations was conducted to verify manufacturer data. Using measurements of the physical generator and manufacturer specifications, a finite element model of the existing generator was created and used as a point of comparison with the proposed shared-rotor and a conventional 13-kW turbo-generator. Comparisons of key figures of merit such as weight, specific power, component losses, and overall efficiency were made between different turbo-generator configurations. The proposed high-current-density, shared-rotor disk configuration had the largest specific power, around 22.5% greater than the proposed turbine with existing generator and around 264% greater than the conventional 13-kW turbo-generator. However, with notable room for improvement, the shared-rotor generator configuration was found to be between 1-5% less efficient than the existing generator coupled to the proposed turbine. The study culminates in broad recommendations for design and implementation of shared-rotor turbo-generator systems.