Secondary flow control in a modern aero-engine fan using vortex generators

Over the years, modern aero-engine compressors have seen a consistent reduction in size and weight, striving for lower fuel-consumption. The distance between blade rows has been shortened, increasing the impact of inter-row flow interaction phenomena. Secondary flows, such as the vortices generated in a blade row and ingested by downstream components, impact the life and performance of fans and compressor stages. The formation and transport of secondary flow vortices can be modified by the presence of several blade passage features, such as gaps, ramps, and bleed-slots. The present work aims at controlling the secondary flows in a modern high-bypass aero-engine fan, through the use of vortex generators (VGs). The physical mechanism of secondary flows formation and the influence of the fan geometrical modeling on their development and transport are investigated and thoroughly described using Rolls-Royce in-house CFD tools (PADRAM-Hydra). Then a constrained aerodynamic optimization is performed, where the VG is parameterized with seven design variables. The optimization is carried out within the GEMSEO open-source framework, using a machine learning surrogate-based algorithm, with evaluations from an initial design of experiments serving as a training set. Additionally, insights into the design parameters influence on the VG/fan system performance are given through the use of the active design subspace methodology. Results show that the optimized VG can significantly reduce secondary flows and the forced response on a generic downstream component, without penalizing the fan's performance.