Jet engines are comprised of many complex components, and overall engine efficiency and fuel consumption depend on the individual performance of these. This thesis investigates the use of novel analysis/design approaches that can lead to improvements in engine component aerodynamic performance, and therefore have the potential to reduce jet engine fuel consumption.
This work focuses on design improvements that can be used to benefit future advanced high bypass ratio engines. Several key engine components are studied: fan blades, compressor blades and engine intakes. The various investigations and outcomes are summarised here.
A novel compressor blade shaping approach that uses free-form parameterisation is first investigated. This is shown to offer the potential to increase blade efficiency over alternative parameterisations. Increased design flexibility and the ability to combine 3D blade shaping with aerofoil section modification allows the maximum benefit to be achieved. It is demonstrated that the off-design performance of the optimised blade is satisfactory, meeting the same choke mass flow (once skewed) and achieving reasonable performance at different rotational speeds.
The use of shock control bumps is found to be beneficial on transonic fan and compressor blades. It is shown that shock control can delay and reduce separation for a highly-loaded compressor blade, increasing its efficiency without the need for 3D deformations of the blade. The benefit of shock control bumps in reducing shock-induced separation is also demonstrated for a modern, low-speed fan blade, providing an increase in stall margin.
Tip clearance effects for modern fan blades are also investigated. The influence of trenches that become worn in the abradable liner is analysed and a model developed that can predict fan blade efficiency for combinations of non-uniform tip clearances and liner trenches. This model allows designers to predict fan efficiency variation over their lifetime and set cold build clearances for optimal lifetime performance. It is also shown how tip leakage behaviour can influence flow behaviour and separation in other regions of the span, and the influence that the shock position has on the leakage aerodynamics.
Through the use of the approaches demonstrated and knowledge developed in this thesis, engineers have the potential to improve future engine designs in terms of efficiency, fuel consumption and also engine operability.
