Open rotor technologies offer the potential for significant reductions in fuel burn and CO2 emissions relative to turbofan engines of equivalent thrust.
Higher propulsive efficiencies are achieved for turbofans by increasing the bypass ratio through increases in fan diameter but there is a diminishing return to this improvement as nacelle diameters and consequently weight and drag increase. Open rotor engines remove this limitation by operating the propeller blades without a surrounding nacelle, thus enabling ultrahigh bypass ratios to be achieved.
Further improvements in propulsive efficiency can be gained for open rotor engines by using a second row of propeller blades rotating in opposition to the front row to remove the spin from the column of air to give a more direct thrust. The technical challenges of counter rotating open rotor engines are many, but are principally:
- Reduction of the noise created by the propeller blades to counter the loss of attenuation provided by a turbofan nacelle.
- Definition of the propeller system to reduce the noise created by the counter rotating blades (counter rotating slotted discs in close proximity is the basis siren design and blade interaction noise was the principal issue noted when the open rotor engines were demonstrated in the 1980s)
- Complexity of communications and blade pitch control through the counter rotating power transmissions system.
- Installation of the open rotor engine on the airframe. Turbofans are isolated from the airframe by the nacelle but the airflow through open rotor propellers interacts with the supporting airframe structure and so the installation impacts on the engine system noise and efficiency.
- Rolls-Royce has developed open rotor propeller design to minimise the noise and demonstrated the effectiveness of these designs through scaled rig testing in the FP7 DREAM programme. The SAGE1 project is planned to aquire technology for the propulsor system, increasing the Technology Readiness Level (TRL) to TRL 5.
Collaborating in the SAGE1 project under Rolls-Royce leadership are Volvo Aero Corporation and ITP. Further Partners will be selected through the Clean Sky Call for Proposal process as the project progresses. Details of these opportunities and the application process will be published on the Clean Sky website: www.cleansky.eu
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The SAGE3 project is focused on low pressure system and externals technologies. Rolls-Royce has been developing composite fan technologies in the FP6 (Framework Programme 6) VITAL and ELF programmes but the technology requires engine demonstration to achieve Technology Readiness Level 6, the environment in which it will operate. The SAGE3 project will include an engine demonstration (the Advanced Low Pressure System, or ALPS, demonstrator) to provide this verification.
Further technology demonstration in the SAGE3 project will focus on advanced externals, with engine demonstration opportunities offered to advanced systems to reduce the weight of the installations. These lightweight integrated sub-systems will focus on utilisation of composite and other lightweight materials, on improved integration of externals with the engine structure and extension of existing lightweight solutions to higher temperature applications. Low pressure turbine technologies will be developed and demonstrated by ITP and compressor intercase technologies by Volvo Aero.
The basis for the engine demonstration will be a Trent 1000 engine and planned testing includes a full range of aerodynamic and noise tests on indoor and outdoor test stands and in flight. Rig testing is planned for components where either this will provide full validation (such as for the intercase technologies) or where a limited engine dataset will verify the results of a more complete rig test survey.
Collaborating in the SAGE3 project under Rolls-Royce leadership are Volvo Aero Corporation, ITP, FACC and University of Rapperswil. Further Partners will be selected through the Clean Sky Call for Proposal process as the project progresses.
Details of these opportunities and the application process will be published on the Clean Sky website: www.cleansky.eu.
The SAGE6 project is focused on delivering a Lean Burn Combustion System demonstrator engine. The aim is to demonstrate a lean burn whole engine system to a TRL6 maturity level, suitable for incorporation into civil aerospace applications in the 30,000lb to 100,000+ thrust classes.
SAGE6 is continuing on from previous demonstrator programmes such as ANTLE/POA, E3E and EFE. The SAGE6 project will include an engine demonstration (Advanced Low Emission Combustion, or ALECSYS demonstrator) to provide this verification.
Further technology demonstration in the SAGE6 project will focus on Lean Burn Combustion Technology, advanced engine health monitoring, advanced cooling technologies, advanced fuel heat management and improved manufacturing capabilities. Current TRL levels of the various subsystems vary, but are typically at TRL3-4. Whilst existing demonstrator platforms (rigs and engines) will be sufficient to develop the system to TRL5, additional capability in the form of a ground demonstrator will be required. This vehicle will encompass the entire lean burn system including the combustor, fuel supply and control system, sensing technologies and the associated externals and installation hardware, and represents a significant set of modifications to the architecture of the Trent 1000 donor engine.
Collaboration in the SAGE6 project under Rolls-Royce leadership is through partners selected through the Clean Sky Call for Proposal process as the project progresses.
Details of these opportunities and the application process will be published on the Clean Sky website: www.cleansky.eu.
