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.
Highlights
Fluid film journal bearings provide lateral rotor support
This review considers the current industrial trends in higher journal surface speeds which lead to increases in turbulent effects and inertia effects in the theoretical models
An experiment that requires less equipment than the other approaches to conduct is the incremental loading of journal bearings to measure the lubricating film stiffness without considering damping or fluid mass data
Summary
Fluid film journal bearings provide lateral rotor support. The support forces and dynamic properties in fluid film bearings arise from the fluid-structure interaction forces between the rotor and the bearing fluid film These properties were originally described by Reynolds using a laminar, isoviscous fluid model. Two distinct approaches to exciting the rotor-bearing system for dynamic coefficient identification have been used. For lubricant flows in fluid film bearings, the approaches are dynamically equivalent and either is valid in measuring bearing coefficients when performed properly. A few have considered the effects of compliant foundations in the total rotor-bearing system With both the regular and inverse approaches, various excitation signal forms have been applied, including sinusoidal, transient, known/additional unbalance, and pseudorandom. Many of the older published reports describing bearing identification experiments have not presented confidence intervals for the measured coefficients, but more recent experimenters have included them in their published work [15,29]
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