Aerodynamic design framework for low-pressure compression systems

Doctoral thesis, 2018

Aircraft engine manufacturers strive to improve current state of the art designs through continuous development efforts. By improving existing designs and exploring new alternatives, the goal is to reduce the fuel consumption - a topic of high relevance due to the remarkable growth rate of air traffc. To achieve a low fuel consumption, turbofan engines should operate at a high overall pressure ratio which is commonly achieved by an axial compressor. An axial compressor consists of a set of consecutive stages, each consisting of a rotating and stationary blade row. While a compressor should operate with a high pressure ratio, it should not operate too close to its stability limit where surge can occur. If surge occur in the compressor, the compressor blades will be subject to large transient forces and the ow may even reverse direction. The main focus of this thesis is the further development of an aerodynamic design framework for low-pressure systems, where an appropriate level of modeling is selected and compressor stages are optimized with respect to effciency and stability. Different approaches are used to evaluate stability of a compressor stage and it is concluded that the static pressure rise capability of the stage is an appropriate measure to use for ranking designs in an optimization. As a part of this thesis, all three stages of a three-stage compressor are optimized using steady state RANS calculations, and the performance of the three-stage compressor is evaluated as an assembly. The possibility of replacing blade geometries to improve part- or design speed stability of the three-stage compressor is shown. Other aspects which may penalize efficiency are investigated, namely the in uence of surface roughness and manufacturing variations on performance. The in uence of surface roughness on optimal stage designs is assessed by optimizing compressor blades with and without taking surface roughness into account. The impact of manufacturing variations on performance at a design point is investigated by utilizing measurements of a manufactured compressor blisk.