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

Abstract

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-size and high-efficiency turbomachinery. However, the coupling of the mechanical properties of the O-rings and lubrication induce strong nonlinear characteristics, thereby affecting the dynamic responses of the rotor. In this study, a numerical model is presented, which is coupled with the excitation frequency-influenced stiffness and damping characteristics of O-rings, the Darcy’s laws, air motion equations established by the air lubrication model, and the rotor and bearing motion equations. The model is well verified by the experimental results. The effect of the different system parameters on the performance of the rotor-PAJB system (RPS) is studied by analyzing the bifurcation diagrams, orbit, Poincaré maps, and FFT plots. Results show that the motion of the rotor 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 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 SBR as the material is better than that with NBR but weaker than that with VMQ. Moreover, only a few number of O-rings have better effects on improving the stability of the RPS.