High-Lift High-Pressure Turbine Blade Tips for Future Aircraft Engines

In order to reduce the emissions from the aviation sector, we must improve the efficiency of aero engines to enable sustainable fuels. A key component in these engines is the High-Pressure Turbine (HPT), which extracts energy from the hot combustor exit gasses. The temperature of the exit gas is several hundred degrees above the melting point of the HPT metal and is continuing to rise to improve engine efficiency. The blade temperature is controlled by injecting cooler air through it and over its surface to shield it from the hot gas, but the use of cooling flows reduce efficiency. We must therefore achieve effective cooling while reducing cooling flow requirements.

We can reduce cooling flow requirements by decreasing the number of blades, and thus surface area, but this puts more aerodynamic load, or lift, on each remaining blade. However, such high-lift blades can suffer poorer aerodynamic performance. In particular, the higher pressure difference between the blade's Suction Surface (SS) and Pressure Surface (PS) tends to drive greater amounts of leakage flow through the clearance gap between the rotor blade tip and the stationary casing. This Over-Tip Leakage (OTL) flow reduces the turbine work output and aerodynamic efficiency.

This project aims to enable the use of high-lift blades by (1) mitigating the higher OTL flow to maintain aerodynamic efficiency, and (2) developing highly effective cooling strategies that reduce the cooling flow requirement.

In order to mitigate OTL flows, partial shrouds, or winglets, and cavities will be studied with high-lift profiles. Since there is little previous work on high-lift OTL flows, this project will take a multi-disciplinary approach to assess aerodynamic and thermal performance, combining analytical, numerical, and experimental methods. The design space will be explored with the use of analytical models, and more complex Computational Fluid Dynamics (CFD) simulations to investigate novel tip designs and cooling configurations. Promising designs will be carried forward to a transonic linear cascade experimental rig which employs aerodynamic probes to measure the flow field, infrared thermography to extract heat transfer coefficients, and pressure sensitive paint with foreign gas injection to determine cooling film effectiveness. Successfully enabling these high-lift designs would reduce emissions by around 3.5 million tonnes of CO2 per year as a result of a targeted 0.3% reduction in fuel consumption.

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.