Endwall Flow Mechanisms in Electric Propulsors

Over the last decades, the dramatic growth of the aviation industry and its emissions has caused an increased interest in the electrification of aviation. The battery and motor technology limit the possible range of electric aircraft, making them suitable only for short missions in urban environments. Due to the infrastructure limitations in these environments, most of these aircraft are designed for vertical take-off and landing (e-VTOLs).
Shaft-driven ducted fans are commonly used for the propulsion of e-VTOLs leading to safe and quiet missions. However, recent research projects suggest that placing the electric motor at the rotor's shroud (Rim-Driven Fan, RDF) could enhance the propulsor's performance. The rim provides support against mechanical stresses, and the motor cooling and wiring become less complex as cables do not cross the gas path. Nonetheless, the rotating shroud would modify the flow field and affect the system's efficiency.
From the existing literature, it is clear that the flow patterns developed at the tip region of the rotor, referred to as endwall flows, affect the aerodynamic loss and stability of ducted fans. Most of the work already done is focused on conventional, cantilevered rotor blades and does not apply to RDFs. Hence, this PhD project aims to analyse the effect of shroud on the aerodynamic performance, in terms of both efficiency and stall margin, and assess the trade-offs between the different designs of fans for e-VTOLs.
Steady and unsteady CFD simulations will be carried out to investigate the flow field developed within the engine throughout the e-VTOL flight mission. Unsteady simulations for such designs have not been conducted in previous studies and are necessary to understand the causes and consequences of flow instabilities appearing under certain operating conditions of the engine. The designs examined will be rapidly manufactured and tested in an e-VTOL dedicated rig in the Whittle laboratory. To assess the feasibility of RDFs an integrated-system approach will be adopted, accounting for the impact of the new design on all the engine components.

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.