Predictions of Dynamic Load Characteristics of Hydrostatic Thrust Bearings

Abstract

Hydrostatic thrust bearings are utilized in process fluid turbomachinery to control axial rotor motion and provide a high axial load capacity on the rotor-bearing system. In compressors, a surge effect, caused by a pressure ratio (discharge pressure/supply pressure), can result in large axial cyclic motion in the impeller, which can damage the compressor system [1, 2]. However, conventional studies have limitations in accurately evaluating the dynamic load characteristics of externally pressurized thrust bearings, as they only consider small amplitude motions using perturbation methods [3, 4]. To accurately predict bearing dynamic load characteristics, it is essential to consider large dynamic amplitude motions of the rotor-bearing system [5, 6]. In this study, a predictive model, validated using Ref. [7], and the predicted results for dynamic load characteristics of hydrostatic thrust bearings are presented. The predictive model solves the Reynolds equation using the finite element method (FEM) and estimates the dynamic stiffness and damping coefficient at air supply pressures of 3 bar(g) and 4 bar(g). The predicted dynamic stiffness of the bearing model with small amplitude axial motions shows good agreement with the measured (estimated) static stiffness in Ref. [8]. However, the predicted dynamic stiffness with large amplitude axial motions shows a significant difference with the test results in Ref. [8]. The work presents a reliable predictive model to investigate the dynamic load characteristics of externally pressurized thrust bearings for various axial cyclic motion amplitudes.