Variable Pitch Configurations for Future Propulsion

Novel propulsive methods with reduced fuel consumption are sought after, for achieving net zero emissions by 2050. Open rotors are an appealing candidate as the removal of the engine nacelle allows the employment of larger fans with lower pressure ratio, without increased weight and drag penalties. Fuel burn benefits with open rotors using contrarotating, variable pitch propellers have been demonstrated with test flights in the 1980s. A pair of contrarotating propellers allows the swirl generated by the first rotor to be recovered by the second rotor and transferred into additional thrust. However, major noise concerns deemed such engines as impractical. Recently, the development of a single-rotor open rotor with rear stators was revealed by the CFM RISE program. Therefore, the feasibility of open rotors must be revisited within the current context. This project investigates the aerodynamic performance of open rotors, and will identify the potential benefits in propulsive efficiency and fuel consumption in comparison to other low fan pressure ratio propulsors. Furthermore, the project will look into the trade-offs of single-rotor open rotors for a range of flight Mach numbers, and investigate improved blade design methodologies for both contrarotating and single-rotor open rotors.
The research aims are addressed through numerical methods, using Computational Fluid Dynamics (CFD). Results have been generated for a computational model of NASA's F31/A31 open rotor test rig, using Turbostream CFD. The loss mechanisms and trade-offs between contrarotating and single-rotor open rotors were identified by a power breakdown analysis. Research will continue by incorporating higher fidelity computational methods such as unsteady RANS simulations.

1. Impact on the UK Aero-Propulsion and Power Generation Industry
The UK Propulsion and Power sector is undergoing disruptive change. Electrification is allowing a new generation of Urban Air Vehicles to be developed, with over 70 active programmes planning a first flight by 2024. In the middle of the aircraft market, companies like Airbus and Rolls-Royce, are developing boundary layer ingestion propulsion systems. At high speed, Reaction Engines Ltd are developing complex new air breathing engines. In the aero gas turbine sector Rolls-Royce is developing UltraFan, its first new architecture since the 1970s. In the turbocharger markets UK companies such as Cummins and Napier are developing advanced turbochargers for use in compounded engines with electrical drive trains. In the power generation sector, Mitsubishi Heavy Industries and Siemens are developing new gas turbines which have the capability for rapid start up to enable increased supply from renewables. In the domestic turbomachinery market, Dyson are developing a whole new range of miniature high speed compressors. All of these challenges require a new generation of engineers to be trained. These engineers will need a combination of the traditional Aero-thermal skills, and new Data Science and Systems Integration skills. The Centre has been specifically designed to meet this challenge.

Over the next 20 years, Rolls-Royce estimates that the global market opportunities in the gas turbine-related aftercare services will be worth over US$700 billion. Gas turbines will have 'Digital Twins' which are continually updated using engine health data. To ensure that the UK leads this field it is important that a new generation of engineer is trained in both the underpinning Aero-thermal knowledge and in new Data Science techniques. The Centre will provide this training by linking the University and Industry Partners with the Alan Turing Institute, and with industrial data labs such as R2 Data Labs at Rolls-Royce and the 'MindSphere' centres at Siemens.

2. Impact on UK Propulsion and Power Research Landscape
The three partner institutions (Cambridge, Oxford and Loughborough) are closely linked to the broader UK Propulsion and Power community. This is through collaborations with universities such as Imperial, Cranfield, Southampton, Bath, Surrey and Sussex. This will allow the research knowledge developed in the Centre to benefit the whole of the UK Propulsion and Power research community.

The Centre will also have impact on the Data Science research community through links with the CDT in Data Centric Engineering (DCE) at Imperial College and with the Alan Turning Institute. This will allow cross-fertilization of ideas related to data science and the use of advanced data analytics in the Propulsion and Power sectors.

3. Impact of training a new generation of engineering students
The cohort-based training programme of the current CDT in Gas Turbine Aerodynamics has proved highly successful. The Centre's independent Advisory Group has noted that the multi-institution, multi-disciplinary nature of the Centre is unique within the global gas turbine training community, and the feedback from cohorts of current students has been extremely positive (92% satisfaction rating in the 2015 PRES survey). The new CDT in Future Propulsion and Power will combine the core underlying Aero-thermal knowledge of the previous CDT with the Data Science and Systems Integration skills required to meet the challenges of the next generation. This will provide the UK with a unique cohort of at least 90 students trained both to understand the real aero-thermal problems and to have the Data Science and Systems Integration skills necessary to solve the challenges of the future.