Nonlinear Transient Analysis of Tilting Pad Journal Bearings Under Starved Lubrication

Abstract

Abstract. Tilting pad journal bearings (TPJBs) have high vibration stability and are widely used in high-speed turbomachinery. In recent years, direct-lubricated TPJBs have been used to reduce bearing losses and bearing metal temperatures at high shaft speeds. However, it is known that direct-lubricated TPJBs can change their vibration characteristics and generate subsynchronous vibrations (SSV) when the oil supply flowrate is insufficient, due to starved lubrication. Modeling of the dynamic behavior of TPJBs under starved lubrication that has been reported so far has been limited to the calculation of stiffness and damping coefficients that linearize the oil film reaction force and stability analysis using them, and to the author's knowledge, there are no examples of numerical evaluation of SSV of TPJBs under starved lubrication using nonlinear transient analysis. In this study, we propose a nonlinear transient analysis model of TPJBs considering starved lubrication and numerically investigate the effects of each design parameter on the nonlinear transient behavior of TPJBs. A rigid Jeffcott rotor model supported by five-pad TPJBs was considered, and its unbalance response was analyzed. A parameter study was then conducted on the effects of pad arrangement which is Load on pad (LOP) and Load between pad (LBP), shaft speed, oil supply flowrate, and specific load. It was confirmed that broadband SSV occurs for both LOP and LBP under conditions of high shaft speed and low oil supply flowrate. It was also confirmed that under low specific load conditions, the SSV of LOP and LBP are similar, but under high specific load conditions, the vibration level of the SSV of LBP is smaller than that of LOP. These trends qualitatively match the experiment results of Decamillo et al. (2008, “Journal Bearing Vibration and SSV Hash,” 37th Turbomachinery Symposium, Houston, TX, Sept. 7–11, pp. 179–194), demonstrating the validity of this analysis model.