A fully coupled model for tribo-dynamic performance analysis of gas foil bearing-rotor system during start-up

The wear taking place on the top foil surface due to asperity contact with the rotor during start-up is a significant contributor to the failure of gas foil bearings. Hence, research on the start-up behaviors of foil bearings is crucial for improving structural design and extending service life. This paper presents a transient model to investigate the tribo-dynamic performance of foil bearing-rotor system during start-up, which comprehensively considers transient hydrodynamic pressure, deflection of the foil structure, dynamic motion of the rotor and multi-domain coupling effect. The Reynolds equation is formulated with consideration of the gas rarefaction and surface roughness effects. Both the top foil and bump foil are modeled using the beam elements, between which the close/loose contacts are considered. To alleviate time-lack issue and improve convergence, this model is numerically solved in a fully coupled manner. A test rig is established for validation. The simulations reveal that the hydrodynamic and asperity contact forces show obvious fluctuations in the initial period of start-up. Subambient pressure occurs within the gas film, causing the separations between the top foil and bumps. Besides, the effects of nominal clearance, acceleration time and surface roughness on the tribo-dynamic performance of foil bearing-rotor system during start-up are evaluated.