A nonlinear model for dynamic performance analysis of gas foil bearing-rotor system considering frictional contacts

The dynamic behaviors of gas foil bearing-rotor system are greatly affected by the damping resulting from friction inside foil structure. However, challenges exist in theoretical study when introducing the friction into the dynamic system. This paper presents an effective nonlinear model considering frictional contacts to study the dynamic performance of foil bearing-rotor system. The top foil and bump foil are modeled with the beam elements to consider the sagging effect and bump interactions. Instead of treating the structural damping caused by friction as equivalent viscous damping, the friction force is calculated by utilizing a regularization technique to capture its nonlinear behavior. The simulations are numerically implemented using a direct implicit integration scheme with consideration of unsteady hydrodynamic pressure, rotor motion, deflection of foil structure and their coupling relationships. Using this model, the dissipative characteristics and stability of foil bearing-rotor system are investigated. The results show that the friction leads to hysteretic loops and energy dissipation, and the stick motion becomes more prevalent with the increasing friction coefficient. The dynamic system exhibits rich and complicated nonlinear behaviors. With the change of system parameters, the rotor can experience periodic, quasi-periodic and multi-periodic motions. Only synchronous vibration occurs at low rotational speeds, but large-amplitude subsynchronous vibrations are dominant when rotational speed exceeds the onset speed of instability. Increasing the nominal clearance contributes to avoid the appearance of subsynchronous vibrations, resulting in a more stable system. The predictions can provide guidance for determining the operating and design parameters of foil bearing-rotor system in practice.