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Distributed Propulsion and Ultra-high By-pass Rotor Study at Aircraft Level

Final Report Summary - DISPURSAL (Distributed Propulsion and Ultra-high By-pass Rotor Study at Aircraft Level)

Executive Summary:
The European Commission Framework Programme 7, Level-0 project entitled Distributed Propulsion and Ultra-high By-Pass Rotor Study at Aircraft Level, or, DisPURSAL has been finalised. Coordinated by Bauhaus Luftfahrt e.V. this 2-year project, which commenced in February 2013, involved partners from Central Institute for Aviation Motors (CIAM, Russia), Office National d'Études et de Recherches Aérospatiales (ONERA, France) and Airbus Group Innovations (Germany). Moreover, the project benefited from expert advice given by an Industrial Advisory Board comprising representatives from Airbus Group Corporate Technical Office (Germany), Airbus Defence and Space (Germany), MTU Aero Engines (Germany), Deutsches Zentrum für Luft- und Raumfahrt (DLR, Germany) and ONERA. Targeting a year entry-into-service of 2035 this project investigated aircraft concepts employing distributed propulsion with focus placed upon one novel solution that integrates the fuselage with a single propulsor (dubbed the Propulsive-Fuselage Concept, or, PFC) as well as Distributed Multiple-Fans Concept (DMFC) driven by a limited number of engine cores. Aspects that were addressed included aircraft design and optimisation, airframe-propulsion integration, power-train system design and advanced flow field simulation.
A synopsis of outcomes and insights for the DMFC were itemized as:
• For a design range of 4800 nm (8890 km) with 340 passengers at M0.80 cruise speed, block fuel burn reduction compared to an appropriate projected-technology, gas-turbine only aircraft utilizing a conventional morphology (dubbed the “2035R”) was predicted to be 7.8% (worst and nominal cases) up to 10.5% (best case)
• Assuming the same range, speed and passenger accommodation the block fuel difference to a year 2000 datum A330-300 aircraft (dubbed the “SoAR”) was found to be nominally -37.3%
• Using methods currently being considered by the International Civil Aviation Organization (ICAO) for upcoming issuance of ICAO Annex 16 Environmental Protection Volume III, nominally 40% lower CO2-emissions versus the SoAR and 7% better than the 2035R were observed; this means the shortfall in CO2-emissions reduction with respect to Strategic Research and Innovation Agenda (SRIA) 2035 is 11% (2035R is 18% shortfall)
• The Consortium found that significant effort needs to be expended in ameliorating the penalizing effects of Boundary Layer Ingestion (BLI), leading to circumferential inlet distortion and diminished fan surge margin when it concerns future activities
• There appears to be a good likelihood of meeting the SRIA 2035 NOx-emissions and external noise targets
• Assuming a nominal fuel price of USD 3.30 per US gallon up to 24% lower Cash Operating Costs (COC, fees and charges due to emissions and noise inclusive) versus SoAR was predicted, equivalently this was found to be approximately 4% better than the 2035R
• A hybrid-electric variant described by a core straddled by two electric fans in serial power-train arrangement was predicted to have nominally +1.5% block fuel versus the 2035R assuming the same design mission
A synopsis of outcomes and insights for the PFC were itemized as:
• For a design range of 4800 nm (8890 km) with 340 passengers at M0.80 cruise speed, block fuel burn reduction compared to an appropriately projected-technology, gas-turbine only aircraft utilizing a conventional morphology 2035R was predicted to be 5.2% (worst case), 9.2% (nominal case) and 11.0% (best case)
• Assuming common part-numbers for all engine cores associated with the PFC, the best and balanced thrust split ratio was found to be 77% for the under-wing podded engines and 23% for the Fuselage Fan device
• Assuming the same range, speed and passenger accommodation the block fuel difference to the SoAR was found to be nominally -38.3%
• Using methods in accordance with upcoming ICAO Annex 16 Environmental Protection Volume III, nominally 42-43% lower CO2-emissions versus the SoAR and 10% better than the 2035R were observed; this means the shortfall in CO2-emissions reduction with respect to SRIA 2035 is 8%
• The Consortium found that significant effort needs to be expended in ameliorating the penalizing effects of BLI of the Fuselage Fan leading to detrimental NOX-emissions when it concerns future activities
• There appears to be a good likelihood of meeting the SRIA 2035 external noise targets
• Assuming a nominal fuel price of USD 3.30 per US gallon up to 25% lower COC versus SoAR was predicted, equivalently this was found to be approximately 5% better than the 2035R
• If the PFC was sized according to an appropriate “optimal speed matching” philosophy, i.e. Long Range Cruise speed of M0.78 instead of M0.80 scope was found to further reduce block fuel and CO2-emissions by approximately another 5% compared to the 2035R; this is approximately an additional 3% reduction in COC compared to 2035R and the time penalty was found to be only +16 mins for an 11-hour, 4800 nm flight
• A hybrid-electric variant described by electric fans driving the Fuselage Fan device in a serial power-train arrangement was predicted to have nominally -7.3% block fuel versus the 2035R assuming the same design mission
Project Context and Objectives:
All too few introductory-level studies have examined the merits of boundary layer ingestion and/or wake filling applied to fixed-wing commercial transports, and no comprehensive effort had been expended in examining more pragmatic implementation according to tenets of potential for evolution, scalability and maximised major-systems synergy. Therefore, in order to address this shortfall, the global objectives of the DisPURSAL Project was to investigate emerging technologies when integrated in the context of distributed propulsion architectures that lead to fulfilment of Flightpath 2050 goals with guidance provided by the Strategic Research and Innovation Agenda (SRIA) 2035 temporal waypoint. Accordingly, a breakdown of the project targets were itemised as:
• By Year Entry-Into-Service (YEIS) 2035, a reduction of 60% in CO2-emissions and 84% in NOx (includes improvements due to Air Traffic Management and operational efficiency) relative to the capabilities of typical aircraft in-service during year 2000;
• By YEIS 2035 a reduction of 55% (equivalent to -11.0 dB) in cumulative external noise relative to the capabilities of typical aircraft in-service during year 2000; and,
• Cash Operating Cost outcome at least 20% better than a typical aircraft in-service during year 2000, and, 5-10% better against a projected year-2035 aircraft utilising a conventional morphology and advanced gas-turbine propulsion technology; and,
The DisPURSAL Project emissions and external noise reduction, and, Cash Operating Cost objectives were to be attained via a two-pronged combined discrete and continuous optimisation approach. The first involved a pre-design study of different alternatives for integrating distributed propulsion technologies for purposes of evaluation and subsequent matching with annexed technologies and novel aircraft morphologies. Multi-disciplinary numerical experimentation utilising mostly quasi-analytical, and where necessary, variable fidelity methods constituted the basis for evaluating the extent of functional sensitivity (strong, moderate or weak) against the aforementioned objectives. Approaching the problem initially from a non-hierarchic perspective, once these influential sizing design variables were identified, strategies were then devised such that an integrated distributed aircraft concept was procured using the multi-disciplinary numerical experimentation techniques discussed above.
Evaluation of the advanced distributed propulsion system concepts investigated in DisPURSAL were to be conducted assuming a projection of contemporary thinking associated with generally accepted “beyond state-of-the-art” approaches from European Commission and various National Framework Programmes. This conspired to ensure, once an aircraft level evaluation was performed, the most aggressive basis for gauging the relative impact. Another important facet that needed to be addressed when evaluating new distributed propulsion concepts was identification of changes to flight technique (speed schedule and altitude profile) based upon objectives of emissions reduction and operating economics. Since operating cost has two fundamental dependencies of fuel burn-off (and energy expenditure) and time, changes to flight technique optimality needed to be considered for a selected number of points on the aircraft payload-range working capacity envelope (to reflect the projected aircraft utilisation spectrum). From an overall aircraft integration and sizing perspective, the evaluation exercise provided new insights regarding departures when it concerns critical sizing cases.

Project Results:
Due to the DisPURSAL Project being a Level-0 endeavour, the S&T foreground is presented in the context of identifying which enabling technologies (components, sub-systems and fully integrated systems) are considered to be key and what attributes said technologies need to possess. The technology freeze year was considered to be around 2030.
Specific to the Distributed Multiple-Fans Concept:
• Hybrid Wing-Body aircraft morphology comprising an airframe made from CFRP structure and installation of Riblets on its skin
• Power transmission facilitated via a mechanical drive gear system described by an angular shafting system in the considered power class unprecedented in aviation history
• Thrust vectoring system and variable area nozzle technologies in order to augment yaw control power for the vehicle
Specific to the Propulsive Fuselage Concept:
• Aircraft morphology and annexed technologies where the wing comprises a CFRP structure, thus providing scope for a slender, very flexible, high aspect ratio design. Omni-directional ply orientation of carbon fibres combined with advanced bonding techniques would serve to realise a light-weight structure throughout the airframe
• Aerodynamic design that incorporates a smooth fuselage surface without excrescences in order to maximize the viscous drag reduction effect attainable from boundary layer ingestion
• Detailed structural analysis of the entire aft-fuselage section including the Fuselage Fan nacelle, tail cone and empennage arrangement under consideration of all relevant load cases. Especially the load carrying nacelle structure and the FF intake struts will require careful aero-mechanical design
• Fuselage Fan and nacelle structural (aero-mechanical) design should take into account potential radial and circumferential pressure distortion patterns during high angle-of-attack and angle-of-sideslip manoeuvres, in particular under consideration of the wing-induced flow field
• Fuselage Fan power transmission effected using a Fuselage Fan Drive Gear System comprising a planetary reduction gear system with focus on minimizing friction losses, external noise and weight while satisfying the requirements regarding reliability and service life with minimum maintenance effort
• Multi-functional and operational aspects include the incorporation of Fuselage Fan Guide Vanes and separation control devices that ensures best performance during all off-design flight conditions
• Thrust reverser and combined spoiler concept through symmetric and asymmetric deployment of blocker panels located around the perimeter of the Fuselage Fan nacelle
Specific to both Distributed Multiple-Fans Concept and the Propulsive Fuselage Concept:
• Engine technology utilising ultra-high by-pass ratio Geared Turbofan technology with more efficient core, especially when highly loaded with additional power off-take requiring an increased Overall Pressure Ratio and increased Turbine-Entry Temperatures. The combustion chamber should feature a correspondingly advanced design in order to compensate the detrimental effects resulting from increased compressor exit temperatures and pressures with respect to NOx-emissions
• Technologies providing minimal distortion of inflow field into the fans in order to yield maximum viscous drag ingestion are currently under investigation
• Detailed aerodynamic investigations of the boundary layer ingestion impact on all types of propulsion systems’ internal aerodynamics, in particular fan efficiency and stability impact. The target should be a distortion-tolerant fan design with possible adoption of passive or active flow control techniques for optimal boundary layer ingestion conditioning
• Advanced acoustic liners for turbofan engines and fans are available in present engines; the technology needs to be adapted to the considered application
• Hybrid-electric power-train that requires basic research regarding hybrid-electric systems architecture and behaviour of associated components, such as High-Temperature Super-conducting (HTS) motors, generators, gear system, converter/controller, Solid State Power Controllers (SSPC), cryo-cooler and HTS transmission system
• Numerical and physical experimental testing to substantiate and enhance the benefits of boundary layer ingestion and wake filling (year 2015-2027), and, extensive testing of technologies to gauge associated performance by way of a flying test bed artefact (year 2020-2030)
Potential Impact:
The technologies investigated in the DisPURSAL Project made use of boundary layer ingestion and wake filling in order to improve engine-airframe integrated efficiency and performance. These techniques served to considerably reduce the drag acting on the aircraft, while at the same time the propulsive efficiency was increased. In conjunction with the airframe-engine integration benefits, synergy effects resulting from the introduction of hybrid energy sources were also investigated. Accordingly, the DisPURSAL Project provided an insight into how step changes in emissions and external noise reduction through innovative integration could be realised using distributed propulsion architectures. The impact of outcomes produced by this project can be summarised as:
1. Climate Impact – affords a means to significantly reduce CO2, NOx, CO-emissions and Unburnt Hydro-Carbons, which infers a potential to ameliorate the detrimental effects on climate change due to commercial aviation
2. Industrial Impact – a technical roadmap for strategic research orientation has been produced, which serves as a segue to the creation of new inter-disciplinary competencies and specialisations, hence creates the potential for new employment opportunities
3. Social Impact – ensure air travel will maintain a measure of affordability whilst not compromising standards of reliability and safety, and, offers the potential of reducing the level of cabin and community noise
4. Political Impact – lends itself to generating policies that benefit all stakeholders, defines a future operational environment covering markets and infrastructure, strengthens links between academic/research institutes and industry, and creates an equivalent level of research in Europe as in the US
Dissemination, Communication and Exploitation activities have been of paramount importance to a research project like DisPURSAL because it is was deemed necessary to maximise its impact and trigger effects across the Project’s entire range of target audiences. In particular, the DisPURSAL Consortium, by fully recognising the above, implemented a dedicated dissemination and exploitation strategy. This is exemplified by the following output:
• 3 journal articles published in the Aircraft Engineering and Aerospace Technology Journal (publisher Emerald Group) and the CEAS Aeronautical Journal (publisher Springer). The publications in the Aircraft Engineering and Aerospace Technology Journal were contributions to a special issue devoted to distributed propulsion and hybrid-energy topics comprising authors from Germany, Italy, the Netherlands, Russia, United Kingdom and the US
• 5 conference papers presented at Council of European Aerospace Societies (CEAS) symposia, a European Aeronautics Science Network (EASN) Workshop and an International Council of Aeronautical Sciences (ICAS) conference
• 6 specially invited talks given at an FP7 Level-0 FANTASSY Project conference, Forum-AE Workshop, Institute of Mechanical Engineers (IMechE) Conference, and Royal Aeronautical Society Greener-by-Design Conference
• Organised in collaboration with Cranfield University and NASA a “Special Conference on Disruptive Green Propulsion Technologies: Beyond the Competitive Horizon” held at the IMechE, London, United Kingdom
• Distributed information about the DisPURSAL Project and exhibited a model of the Propulsive Fuselage Concept at the 2014 Berlin-ILA Air Show

List of Websites:

http://dispursal.eu/

Dr Askin T. Isikveren
Head of Visionary Aircraft Concepts
Deputy to Executive Director, Research and Technology
Bauhaus Luftfahrt e.V.
Willy-Messerschmitt-Strasse 1
85521 Ottobrunn
Tel.: +49 (0)89 307 4849-47
Mob.: +49 (0)160 717 0756
Fax: +49 (0)89 307 4849-20
E-Mail: askin.isikveren@bauhaus-luftfahrt.net
Web: www.bauhaus-luftfahrt.net
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