Identification Methods and Test Results for Tilting Pad and Fixed Geometry Journal Bearing Dynamic Coefficients – A Review

Abstract

Fluid film journal bearings (FFBs) are used to support high-speed rotors in turbomachinery which often operate above the rotor first bending critical speed. The FFBs provide both lateral support and dynamic coefficients: stiffness, damping, and mass terms, related to machine vibrations. Detailed numerical values of the bearing dynamic characteristics are necessary for proper design and operation of rotating machinery.The methods of the identification of fluid film journal bearing static and dynamic characteristics, particularly the bearing stiffness, damping, and mass coefficients, from measured data, obtained from different measurement systems, is reviewed. Many bearing tests have been performed to validate a number of different theoretical models, including the classical Reynolds isoviscous model. More advanced bearing models include the thermohydrodynamic (THD), and thermoelastohydrodynamic (TEHD) approaches. The advanced models also include turbulence effects which are important as rotor speeds continue to increase. The range of measured bearing data no longer includes current operational conditions.The various approaches to the bearing identification problem are discussed, including the different force excitation methods of incremental loading, sinusoidal, pseudorandom, impulse, known/additional unbalance, and non-contact excitation. Also bearing excitation and rotor excitation approaches are discussed. Data processing methods in the time and frequency domains are presented. Methods of evaluating the effects of measurement uncertainty on overall bearing coefficient confidence levels are reviewed.In this review, the relative strengths and weaknesses of bearing identification methods are presented, and developments and trends in improving bearing measurements are documented. Future trends in journal bearing identification improvement are discussed.

Experimental and Numerical Simulation of Unbalance Response in Vertical Test Rig with Tilting-Pad Bearings

“…The stiffness matrix of the model includes bearing properties as a function of current eccentricity and load angle, (3) and (4). The stiffness and damping matrix of the bearing, K and C , must be updated in each time step with respect to load angle and shaft eccentricity, which results in a recalculation of A in each time step.…”

“…Historically both numerical simulations and experimental studies in test rigs have been performed to evaluate properties of tilting pad bearings [3,4]. Glienicke et al [5] performed tests in a horizontal test rig consisting of a rotor and bearings.…”

The Experimental Identification of the Dynamic Coefficients of two Hydrodynamic Journal Bearings Operating at Constant Rotational Speed and Under Nonlinear Conditions

“…A summary of the values of errors obtained for ten or so cases described in the literature was prepared by T.W. Dimond et al and Brought to you by | MIT Libraries Authenticated Download Date | 5/12/18 10:40 AM presented in paper [9]damping, and mass terms, related to machine vibrations. Detailed numerical values of the bearing dynamic characteristics are necessary for proper design and operation of rotating machinery.…”

“…Values of stiffness and damping coefficients of hydrodynamic bearings are the most important from the point of view of dynamical performance [12,13]. Because of many difficulties in numerical modelling, many experimental methods for determination of their values have been proposed [9,21]. Experimental investigations were performed with different types of bearings.…”

Experimental Estimation of Journal Bearing Stiffness for Damage Detection in Large Hydrogenerators

“…These authors emphasize the need of experimental work, using full-scale rotor systems, and the need for validation of dynamic coefficients derived from actual machines in the real operating environment. In a more recent review, Dimond et al [14] compared theoretical and experimental results, obtained in test rigs, under controlled conditions. This reference brings attention to the uncertainty analysis in the estimation of bearing coefficients and highlights the need of using TEHD models to theoretically determine these coefficients and to consider the effects of bearing heat transfer and of mechanical deformations.…”