Analysis of a Modern Fan Manufacturing Variations and its link to the Engine Performance

Authors

Shahrokh Shahpar  - Rolls-Royce Group PLC, United Kingdom

Abstract

Every manufacturing procedure is subject to tolerance variations. Over the years, a set of Key Characteristic Features (KCF) that can explain the effect of manufacturing variations on the aero-mechanical performance of a fan blade is devised and monitored to ensure conformality and good performance. The KCFs are derived from a cloud of Coordinate Measurement Machines (CMM) points and are defined on approved engineering drawings for the manufactured part. This paper deals with following four distinct research questions: 1)      Considering the fan of a modern high-bypass ratio engine is responsible for 60-70% of the thrust, it is reasonable to expect geometrical variations within the LP system to contribute significantly to any engine anomaly observed. However, are the current KCFs adequate to explain any engine performance deviation behaviour on a test bed at sea-level? And how does this relate to other important flight conditions (like max take-off and cruise)? 2)      Can a deviation measured via CMM or 3D structured light (GOM) data in cold conditions be translated to a variation in the hot “running” shape? Or does every blade need to be run-up separately? In other words, is the shape variation from nominal independent from the operating conditions? 3)      Discovering that the current set of KCFs may not be adequate to explain the observed variations, what other geomaterial features can be identified to enhance our understanding of the root-cause of any deviations observed? In that respect, the deviations can be parameterized via a set of compact inverse-mapped parameters (from the PADRAM design space) that are able to morph an existing blade onto a shape closely resembling the cloud of CMM data. The optimal values for these parameters are obtained via a novel optimisation methodology [1] 4)      Having identified the key blade features, can the fan blade shape be further altered and optimised to produce a more robust blade? In order to answer these research questions, Rolls-Royce internal high-fidelity and optimisation codes (SOPHY [2]) were used in conjunctions with a large amount of the engine inspection data. In the main paper, the proposed methodology will be compared with the simpler and widely used approach of explaining the performance variability in terms of only the tip stagger angle variation. References [1] Shahpar, S., “Building Digital Twins to Simulate Manufacturing Variation”, Proceedings of the ASME Turbo Expo 2020, GT2020-15263, June 22-26, 2020, London, England. [2] Shahpar, S., “SOPHY: An Integrated CFD based Automatic Design Optimisation System”, ISABE-2005-1086, Jan 2005.