Nonlinear dynamic analysis of a rotor-bearing system with porous tilting pad bearing support

Abstract

Porous tilting pad bearings (PTPBs) show a potential for using in high-speed, high precision rotating machinery that requires high bearing stiffness and good stability. In this study, the nonlinear characteristics of a rotor supported on PTPBs are investigated. The Darcy equations and the modified Reynolds equations are adopted to establish the gas flow model in porous materials and gas film region, respectively. The pad motions and rotor motions are also included in the numerical nonlinear model. The advantages of PTPBs over tilting pad journal bearings are discussed. PTPBs with externally pressurized gas can avoid friction during startup and shutdown, improve the load capacity at low rotational speeds, and effectively suppress subsynchronous vibrations at high rotational speeds. The nonlinear characteristics of the rotor-bearing system with various bearing parameters, such as supply pressure ratio, nominal bearing clearance, pad tilting and radial stiffness, are analyzed. Poincare maps, predicted rotor orbit and bifurcation diagrams are used. High supply pressure ratio and small nominal bearing clearance can significantly decrease the orbit size and increase the critical speed. Low tilting and high radial stiffness can improve system stability. This study reveals the complex nonlinear characteristics of the system and provides guidance for designing PTPBs for using in high-speed rotating machinery.