Propulsor Selection for Electric Aircraft

The market for electrically-propelled aircraft is expected to increase dramatically over the coming decades. This has been driven in large part by both the Urban Air Mobility (UAM) market and by the desire to reduce the aviation industry's emissions by electrifying the propulsion system. However, the design space for electric propulsion has yet to be fully characterized and it is still unknown what the ideal propulsor for a given airframe, range, payload, altitude, or speed is. This has resulted in a 'free-for-all' of propulsive designs emerging in the Urban Air Mobility (UAM) market in which nearly every new flying electric aircraft concept is propelled differently. Therefore, this Ph.D. aims to characterize and explore the design space for electric propulsors.
The proposed Ph.D. will shed light on the design space for electric propulsors by developing a propulsor selection tool, which, when given a set of mission parameters for an electric flight, will design and select the mission's optimal propulsor. This tool will allow for visualization and quantification of the performance trade-offs between designs and will demonstrate which propulsive method is the most-appropriate for a given mission.
Current electrically propelled aircraft designs have employed airframe-first design techniques which have not placed enough emphasis on propulsor selection. This has resulted in sub-optimal designs that end up limiting the efficiency and range of electric aircraft. Additionally, current design techniques differ for propellers and ducted fans. This has resulted in no convenient way to quantify the lost efficiency from propulsors in terms of their design parameters.
Therefore, the proposed Ph.D. will seek to unify the design methodologies for ducted fans and propellers so that these propulsors can be measured and compared in terms of their energy and loss. This will be achieved by modifying and improving upon an existing ducted fan design tool code developed in the Whittle Lab. The proposed methodology for the design tool consists of low order calculations that have been verified both experimentally and computationally to determine the entropy generated by each design. The entropic losses are then used to predict the propulsive efficiency of each technology at a given thrust.
The propulsor selection tool will be able to visualize the design space of electric propulsion and inform electric aircraft designers on the ideal propulsor for their given mission. This will increase the range and performance of electrically driven aircraft. Furthermore, this tool could be useful to investors who want to better understand the electric propulsor design space and know the possibilities and limitations of current electrically propelled aircraft designs.

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.