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

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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.