PhD Studentship - Advanced Air Foil Journal Bearing Rotor System Dynamics - Time Transient & Limit Cycle Orbit Simulation

Research theme: Dynamics

How many positions: 1

This 4 year PhD project is open to home students. The successful applicant will be awarded a tax free annual stipend set at the UKRI rate (£19,237 for 2024/25) and tuition fees will be paid.

Air foil bearings (AFBs, also known as foil air bearings or gas foil bearings) are the key enablers of environmentally-friendly oil-free turbomachinery, including hydrogen fuel cell turbomachines. AFBs support the shaft by creating a cushion of air between the rotating part and a flexible foil structure, which includes a top foil and an underlying supporting foil. The air film pressure develops by hydrodynamic action as a result of the relative motion between the rotating part and the non-rotating top foil. Such bearings can either be journal bearings or thrust bearings, which are used to support loads that are radial (perpendicular to the shaft) and axial (along the shaft), respectively. In both cases, the foil structure comprises a top foil supported by an underlying foil structure which acts as a supporting spring. This project concerns journal AFBs and associated nonlinear vibration issues. As with all fluid bearings, rotor systems fitted with journal AFBs are susceptible to sub-synchronous vibrations that have their origin in the self-excitation phenomenon (similar to oil whirl/whip in oil bearings) linked with the instability (Hopf bifurcation) of the equilibrium state beyond a certain speed. Although predictions of sub-synchronous vibrations with current codes have shown good correlation with experiments under controlled lab conditions, this was only up to a certain speed. Beyond such a speed, the size of the predicted sub-synchronous oscillation (limit cycle orbit) causes the solution to diverge. On the other hand, test data for turbomachines using AFBs show controlled oscillations across the full speed range, including where sub-synchronous vibrations are significant. The proposed project is focused on addressing this limitation through the development of a methodology to deliver simulations over a wider operating regime than currently possible. The realisation of this aim involves the advancement of the modelling of the air film and the foil, and their interaction with the journal (rotating part). The PhD will be conducted in collaboration with Cummins Components and Software (CCS) [Turbochargers Group] who are developing fuel cell turbomachines which use foil air bearing systems. Test data for experimental validation will be obtained from a laboratory rig and from test results provided by CCS.

Applicants should have, or expect to achieve, at least a 2.1 honours degree or a master’s (or international equivalent) in a relevant science or engineering related discipline.

To apply, please contact the supervisor for this project, Dr Bonello - philip.bonello@manchester.ac.uk. Please include details of your current level of study, academic background and any relevant experience and include a paragraph about your motivation to study this PhD project.

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