Dynamic characteristics and wear performance of foil bearings during start-up

The complex structure and strong coupling relationships present significant challenges in studying the dynamic characteristics and wear performance of gas foil bearing-rotor system during start-up. Currently, most numerical studies simplify the start-up process as a sequence of steady operating conditions and neglect the transient rotor motion. Hence the dynamic characteristics during start-up remain inadequately studied. In this paper, a dynamic model is developed to study the start-up performance of foil bearings with consideration of the rotor motion. Additionally, few numerical works have considered the axial variation of the foil structure deflection, although experimental works have observed axially non-uniform distribution of bearing wear. To address this, the model employs a three-dimensional representation of the foil structure utilizing shell elements, with the Guyan reduction method adopted for computational efficiency. Due to the complicated coupling relationships between different domains, a simultaneous solution scheme is developed to solve the numerical model in a fully coupled way. The model is validated by experiments. The analysis indicates that the hydrodynamic pressure, asperity contact pressure and wear distribute non-uniformly along the axial direction during start-up, highlighting the importance of accounting for the axial variation of the foil structure deflection. Reducing the surface roughness or rotor mass can effectively reduce the wear of foil bearings during this operational phase.