Advanced Methods for Propulsion System Integration in Aircraft Conceptual Design

The development of future air transport systems is highly challenged by the rigorous demands for the enhancement of fuel efficiency, transport capacity, system safety, affordability and environmentally friendliness. The advancement of propulsion system technology represents a major element in meeting the drastic demand for reduced fuel consumption, exhaust and noise emissions. Radical propulsion technologies featuring extremely high propulsive efficiencies due to reduced specific thrust levels are considered potential candidates for future aircraft. The corresponding large propulsor dimensions pose significant challenges to propulsion system / airframe integration. The reliable evaluation of new propulsion concepts at early stages of technological development requires an integrated design and performance analysis on aircraft system. In this thesis, a comprehensive approach to incorporating the design of advanced propulsion system concepts in the aircraft conceptual process is presented. The challenges connected to this multidisciplinary design problem are tackled by a rigorous discipline-oriented aircraft conceptual design procedure. Engine conceptual design and performance mapping is based on the software GasTurb 11, and subsequently integrated in the aircraft disciplinary analysis tasks via neural network based surrogate models. For the data sampling required during surrogate model creation and validation, a new approach is introduced using GasTurb 11 computer engine decks. For the conceptual mapping of future propulsion system technology, including the corresponding system installation implications and operational requirements, a consistent set of aircraft and engine conceptual design methods is formulated. The mapping of propulsion system design aspects involves the prediction of turbo component efficiencies, duct losses, propeller aerodynamics, as well as engine operational behaviour, dimensions and weight. The implications of propulsion system design and installation on aircraft design and sizing are discussed in detail. Classic conceptual design methodology is extended to adequately account for the integration of ducted and unducted (“open rotor”) propulsion concepts. The developed methods for system design and analysis are implemented in the proposed discipline-oriented aircraft synthesis process. The discipline-oriented conceptual design procedure is verified, validated and demonstrated based on selected design and analysis applications. The presented studies include the comparative design investigation of advanced direct-drive turbofan and open rotor powered medium range aircraft. For advanced technology settings, design block fuel reductions of approximately 26% were computed for the turbofan engine concept, at typical cruise conditions. For the technologically equivalent open rotor concept additional fuel savings of approximately 9% were identified, while the advantage in thrust specific fuel consumption was more than 16%. The fuel burn benefit for the open rotor concept, however, were clearly reduced relative to the fuel savings predicted in the past. The gained results underline the importance of considering the system-level impact of new propulsion system concepts, in order to assess the true efficiency potentials relative to advanced conventional technology.