Nonlinear Dynamic Analysis of a Rotor-Porous Air Journal Bearing System With O-Rings Mounted

Porous air journal bearings (PAJBs) with O-rings mounted are regarded as a potential choice to offer air levitation with a large load capacity and optimal start/stop characteristics, which are required in small-sized and high-efficiency turbomachinery. However, the coupling of the mechanical properties of the O-rings and lubrication induces strong nonlinear characteristics, thereby affecting the dynamic responses of the rotor. In this study, a numerical model, which is obtained by coupling the excitation frequency-influenced stiffness and damping characteristics of O-rings, Darcy’s laws, air motion equations, and rotor and bearing motion equations, is presented. The numerical model can efficiently reflect the influences of the actual mechanical property of O-rings and the coupling between aerodynamic and aerostatic effects on the performance of a rotor-PAJB system (RPS). The model is well verified by experimental results. The effects of different system parameters on the performance of the RPS are studied by analyzing bifurcation diagrams, orbit, Poincare maps, and fast Fourier transform plots. Results show that the rotor motion is changed between periodic and quasi-periodic with the variation in rotational speed, external supply pressure, bearing clearance, and porous permeability. With O-rings mounted, the stability of the RPS can be increased to hinder the rotor motion from changing from periodic to quasi-periodic. The effectiveness in increasing the stability of the RPS for the O-rings with styrene butadiene rubber as the material is better than that with nitrile butadiene rubber but weaker than that with methyl vinyl silicone rubber. Moreover, only a limited number of O-rings have enhancing effects on the stability of the RPS.