Vibration due to Rotordynamics in Rolls-Royce UltraFan Architecture

The purpose of this research is to improve the understanding of rotordynamics in the new Rolls-Royce UltraFan architecture, and develop novel solutions to tackle the challenges presented by the new architecture. The two areas of focus will primarily be wave speed coincidence in the fan system, and various rotordynamic issues associated with the long high pressure rotor design (consisting of a 10 stage compressor and 2 stage turbine). Once a better understanding is established, solutions other than the usual fixes, such as dampers, will be explored from a more fundamental approach.

An initial assessment will make use of existing data, and some preliminary assessment if required, to compare the impact and probability of the risks in rotordynamics and prioritise accordingly. This may include the effects of wave speed coincidence, rotor internal damping, Thomas/Alford forces, unbalance, rotor bow (mainly due to post-shutdown distortion), asymmetries in bearing support stiffness and tip rubs.

Based on the preliminary assessment, priorities will be placed to address the causes which will add the most value to the UltraFan development. Existing analytical or experimental methods can be chosen and modified following a literature review, or new methods produced if required, to quantify the impact on engine behaviour. Design solutions will then be developed, in collaboration with the Rolls-Royce design teams, which are then analysed and down-selected.