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-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, Poincaré 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.
Highlights
Air bearings have the advantages of simple structure, high precision, and low friction [1]
Porous air journal bearings (PAJBs), which are a special type of aerostatic bearings, restrict the external pressured air by using the porous material to obtain a larger load capacity and better start/stop characteristics compared with the aerodynamic bearings [2]
Refs [8, 9] found that the whirl instability is still a problem for PAJBs used under high rotational speed
Summary
Air bearings have the advantages of simple structure, high precision, and low friction [1]. Miyanaga et al [20] performed the linear perturbation and the nonlinear transient methods to analyze the effect of support stiffness and damping of O-rings on the stability characteristics of herringbone-grooved aerodynamic journal bearings. Waumans et al [24] used elastomeric O-rings in combination with a tunable squeeze film damper as the elastomer suspension in the experimental test to solve the dynamic stability problem of high-speed air bearings. The numerical results of the rotor dynamic characteristics of the RPS are first obtained by coupling the experimental tested stiffness and damping of the O-rings. The rotor orbit, FFT, Poincaré maps, and bifurcation diagrams are adopted to systematically analyze the stability of the RPS in various parameters, including the materials and number of O-rings, rotational speed of the rotor, air supply pressure, nominal clearance, and permeability of the porous material. The displacement of the rotor relative to the center of bearing, which is called relative displacement, in the x- and y-direction can be expressed as follows: xrel yrel
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call