Maintenance of Jet Engines: Robust Parametrisation and Reconstruction of Compressor and Turbine Blades

Abstract Maintenance, repair and overhaul (MRO) of jet engines rely on geometric inspection and aerothermodynamic performance analysis of compressor and turbine blades. Therefore, previous studies have developed various airfoil parametrisation and reconstruction methods to analyse (i) the variability of airfoil parameters due to manufacturing tolerances and deterioration effects and (ii) the impact of the geometric variability on jet engine efficiency. However, the parametrisation and reconstruction methods used in previous studies were adapted for blades and vanes of specific compressor or turbine stages, while generalpurpose methods have not been developed yet for stator vanes and rotor blades. Therefore, this study compiled nominal and measurement data for several compressor and turbine stages of four different commercial turbofan engines. This data was subsequently used to develop general-purpose parametrisation and reconstruction methods based on new approaches for (i) the determination of the camber line, (ii) the mathematical description of airfoil profiles at leading and trailing edges, and (iii) the reconstruction of airfoil shapes. The parametrisation and reconstruction of both nominal and measurement data show that the methods are robust and reliable and provide accurate results. The methods can be utilised for the geometry analysis of non-nominal (especially deteriorated) blades and for the geometry alteration of nominal blades to investigate deterioration effects. Furthermore, the analysis demonstrates that robust methods should have fewer underlying assumptions and more complex software routines compared to tailored approaches for specific compressor or turbine stages. Such routines are, in particular, recommended for nominal blades of high-pressure turbines and deteriorated blades.