Session: 23-03 Oil & Rolling Element Bearings

Paper Number: 151636

Nonlinear Transient Analysis of Tilting Pad Journal Bearings Under Starved Lubrication 

Tilting pad journal bearings (TPJBs) have high vibration stability and are widely used in high-speed rotating turbomachinery. In recent years, direct-lubricated TPJBs are used to reduce bearing losses and bearing metal temperatures at high speeds. However, it is known that when the oil supply flow rate is insufficient in direct-lubricated TPJBs, starved lubrication changes the vibration characteristics, resulting in sub-synchronous vibration. Modeling of the dynamic behavior of TPJBs under starved lubrication reported so far has been limited to the calculation of spring and damping coefficients linearizing the oil film reaction force and stability analysis using these coefficients, and to the author's knowledge there are no examples of numerical study of sub-synchronous vibration of TPJBs under starved lubrication using nonlinear transient analysis.

In this study, a nonlinear transient analysis model of TPJBs under starved lubrication is presented and the effects of each design parameter on the nonlinear time transient behavior of TPJBs are numerically investigated. The oil film reaction force at each pad varies with the oil supply flow rate at the pad inlet, which is determined by the sum of the carryover oil from the upstream pad and the flow rate from the oil supply nozzle, and is obtained by solving the Reynolds equation with the mass conservation law cavitation model (p-θ model) applied at each time step by the finite volume method. The dynamic response of the system consisting of the rotor, bearing pads, nonlinear oil film reaction force, and rotor unbalance force, is solved using the generalized alpha method.

A rigid Jeffcott rotor model supported on five pads TPJBs is considered and its unbalance response is analyzed. Then, the effects of load direction (LOP/LBP), rotation speed, supply flow rate, and bearing specific load are studied. It is confirmed that starved lubrication spreads from the unload pad to the load pad as the speed increases and the supply flow rate decreases. At low specific load, all pads become starved lubrication and low-frequency sub-synchronous vibration is generated under high-speed rotation and low supply flow rate for both LOP and LBP.  At high specific load, although all pads were starved lubricated under high speed and low supply flow rate conditions, the sub-synchronous vibration level of the LBP was lower than that of the LOP. These trends are qualitatively consistent with the experoment results of Decamillo et al (2009), indicating the validity of this analytical model.

Presenting Author: Tasuku Masuda Department of Mechanical Systems Engineering, Nagoya University

Presenting Author Biography: Tasuku Masuda is a PhD student at Nagoya University in Japan, with nine years of experience in the R&D department at a heavy industrial manufacturer. His research specializes in fluid film bearings and rotor dynamics.

Authors:

Tasuku Masuda Department of Mechanical Systems Engineering, Nagoya University
Tsuyoshi Inoue Department of Mechanical Systems Engineering, Nagoya University