Comparison Studies of Dynamic Characteristics for Coupled Bearing-Rotor Systems with Fixed and Pivot-Supported Pads

The coupled bearing (including four-pad tilting pad journal bearings and six-pad tilting pad thrust bearings) is mainly used in a nuclear power circulating pump to support the high axial loads and radial loads from a vertical rotary system with minimum power loss, low vibration, and high load capacity. Its lubrication and vibration characteristics have significant effects on the dynamic performance and operation reliability of the nuclear power circulating pump. In this paper, an original mixed-lubrication dynamic model for the coupled bearing-rotor system is proposed to study the dynamic characteristics of the system considering the effects of the pivot clearance, asperity contact, and elastic deformation. The innovation of the proposed model is that it integrates the horizontal-rocking vibrations of the rotor and pivot pads with the mixed lubrication of the coupled bearing. The coupling effects between the dynamic characteristic of the rotor and the lubrication behavior of the coupled bearing are revealed. In addition, the time-dependent dynamic performance of the fixed pad coupled bearing and the tilting pad coupled bearing are compared. Numerical results indicate that the self-adaptive tilt of the pad makes the oil film pressure more evenly distributed on each pad of the journal and thrust bearings. The tilting pad coupled bearing can effectively improve vibration resistance, system stability, and load-sharing capacity compared to the fixed pad coupled bearing. It is expected that the proposed mixed-lubrication dynamic model can provide guidance for improving the lubrication performance of the coupled bearing and the stability of the system.