Dongil Shin

This paper investigates the journal asymmetric temperature-induced thermal bow vibration of a rotor, as supported by a flexure pivot journal bearing (FPJB). Thermal bow-induced vibration, known as the Morton effect (ME), is caused by non-uniform viscous heating of the journal, and the resulting thermal bow often causes increasing vibration amplitudes with the time-varying phase. Full FPJB’s structural and thermal finite element models are developed and integrated into the flexible rotor model. The model is validated by comparing its predicted ME response with experimental results. An FPJB model, which uses predicted “equivalent” radial and tilting stiffness of the bearing, is compared with the full finite element method (FEM)-based model. The impact of FPJB’s design parameters such as web thickness, bearing material, and housing thicknesses are investigated with parametric studies. The results show that FPJB parameter values may have a major effect on the speed range of ME vibration, and its severity.

The Morton effect is a synchronous vibration problem in turbomachinery caused by the non-uniform viscous heating of the hydrodynamic bearing’s lubricant. This leads to hot and cold spots around the journal circumference and a resultant thermal bow. This thermal bow is mostly associated with overhung-type rotors which tend to generate larger inertial forces and asymmetric viscous

The Morton effect (ME) is a thermally induced vibration problem observed in a rotor supported by hydrodynamic bearings. The journal’s synchronous orbiting induces nonuniform viscous heating on its circumference, and the ensuing thermal bow often causes unacceptable vibration levels in the rotor. This paper investigates the influence of the tilting pad journal bearing (TPJB)’s pivot design on the severity and instability speed range of ME vibration. Simulations are conducted with two different types of pivots: cylindrical (CYL) and spherical (SPH), which produce different pad degrees-of-freedom and nonlinear pivot stiffness due to their geometries. The friction between pad and pivot, which only exists with the spherical pivot, is modeled, and its impact on the ME is evaluated. The example rotor model, as obtained from the literature, is single overhung, with experimentally measured excessive vibration and large journal temperature differentials, near 8000 rpm. The bearing and journal are modeled with three-dimensional (3D) finite elements, and the shaft with flexible beam elements for ME simulation. Nonlinear transient simulations are carried out for a wide operating speed range with varying pivot design parameters. Simulation results indicate that the predicted ME instability is sensitive to the pivot shape, pivot flexibility, and pad-pivot friction.

Nonlinear elements found in fluid film journal bearings and their surrounding structures are known to induce sub- and super-synchronous, chaos and thermally induced instability responses in rotor-bearing systems. The current review summarizes the literature on journal bearing induced nonlinear, rotordynamic forces, and responses. Nonlinear, thermo-elasto-hydrodynamic (TEHD) aspects of journal bearings has become increasingly important in high-performance turbomachines. These have significant influence on bearing dynamic performance and thermally induced, rotordynamic instability problems. Techniques for developing TEHD bearing models are discussed in the second section. Nonlinear solution methodology, including bifurcation determination and time and frequency domain methods such as harmonic balance, shooting and continuation, etc., is presented in the third section. Numerical tools to determine nonlinear vibration responses, including chaos, along with examples of bearing induced nonlinear vibrations are presented in the fourth and fifth sections, respectively.

The Morton effect (ME) is a synchronous vibration problem in turbomachinery caused by the nonuniform viscous heating around the journal circumference, and its resultant thermal bow (TB) and ensuing synchronous vibration. This paper treats the unconventional application of the SFD for the mitigation of ME-induced vibration. Installing a properly designed squeeze film damper (SFD) may change the rotor's critical speed location, damping, and deflection shape, and thereby suppress the vibration caused by the ME. The effectiveness of the SFD on suppressing the ME is tested via linear and nonlinear simulation studies employing a three-dimensional (3D) thermohydrodynamic (THD) tilting pad journal bearing (TJPB), and a flexible, Euler beam rotor model. The example rotor model is for a compressor that experimentally exhibited an unacceptable vibration level along with significant journal differential heating near 8000 rpm. The SFD model includes fluid inertia and is installed on the nondrive end bearing location where the asymmetric viscous heating of the journal is highest. The influence of SFD cage stiffness is evaluated.

Traditional analysis of journal bearings assumed a constant viscosity which simplified the solutions for static and dynamic characteristics and responses. Today's high-performance machinery requires more accurate models wherein temperature and viscosity distributions in the film must be calculated. Thermal effects in journal bearings have a strong influence on both static and dynamic properties, and consequently play a critical role in determining rotor-bearing system performance. This paper presents an extensive survey of the thermal modeling methods and effects in journal bearings. The subjects include various bearing types, and recent progress in thermal bearing design and thermal instability problems observed in fluid and gas film hydrodynamic bearings. The extent of the survey ranges from conventional Reynolds equation models to more advanced computational fluid dynamics models.

This paper investigates the influence of misaligned journal bearing effects on the thermally induced rotor instability (Morton effect “ME”) problem. The Morton effect is caused by uneven viscous heating of the journal in a fluid film bearing, which causes thermal bending, especially in rotors with an overhung disc or coupling weight. The thermally induced bending in the shaft may cause a vibration instability, which results in an excessive level of synchronous vibration. Previous research focused on parametric studies of the rotor and bearing design parameters, including overhung mass, bearing radial clearance, and lubricant viscosity. The present study investigates the influence of journal misalignment on the Morton effect. A coupled fluid-thermal-structural, three-dimensional finite element model (FEM) is developed to simulate fluid film pressures and temperatures, and shaft temperatures and vibrations. Simulations were conducted with different ratios of journal misalignment, and different pad-pivot types to determine their effect on the phenomenon. The simulation results indicate that the amplitude of the misalignment angle affects the instability speed range (ISR) caused by the Morton effect under certain conditions.