Damage effects on the windmilling aerodynamics of low pressure ratio fans

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During engine operation, if there is an engine shut-down, the engine will enter a windmilling state, where the fan will continue to spin due to the ram pressure but no work will be generated. It is critical in the development of future low pressure ratio turbofan designs to characterise the drag and rotational speed of the engine fan at windmill. This project aims to address this, by using both numerical and experimental methods to investigate the aerodynamic flow field at windmill. As this condition will often occur following damage to the engine, blade damage will also be considered during the investigation. A single stream vertical low speed rig in the Whittle Laboratory will be modified to be representative of a future turbofan engine design. These modifications will include the redesign of hub and casing lines, as well as the rotor and stator blades. The blades will be further modified in the later stages of the project to include typical in-service damage patterns. Measurements will then be taken in this rig to investigate the fan flow field at windmill. The experimental study will be complemented with numerical simulations of the fan design with and without blade damage. The main expected outcomes from this project are design recommendations for future low fan pressure ratio engines, as well as the development of a low order modelling tool that can be used in industry to predict drag and rotational speed of the fan in windmill for different blade damage levels.