Prediction and Nonlinear Analysis of Dynamic Gas Foil Bearing-High-Speed Rotor System

Abstract

To address the instability problem of foil-driven hydrodynamic gas bearing-rotor systems in high-speed oil-free rotating machinery, this paper establishes a high-fidelity transient multi-field coupled dynamic prediction model. The core of this model is that it skips the traditional linear stiffness/damping simplification and directly obtains the transient film force by solving the unsteady Reynolds equations that account for the squeezing effect. The paper details the numerical process of solving the transient flow field using the Alternating Direction Implicit (ADI) method and integrates it with the Timoshenko beam finite element rotor model. The transient response of the rotor under aeroelastic coupling effect is simulated using the prediction-correction multi-field coupled trajectory method. The bifurcation evolution law of the system over a wide speed range is investigated in detail. The study finds that after exceeding the critical speed of 14000 r/min, the system undergoes Hopf bifurcation induced by instability at the equilibrium point, subsequently evolving into a limit cycle motion with significant subsynchronous characteristics. With further increases in speed, the subsynchronous eddy frequency ratio evolves from 0.5X to 0.21X, revealing the frequency modulation mechanism caused by the nonlinear film force.