Multi-orifice active tilting-pad journal bearings—Harnessing of synergetic coupling effects

The dynamic performance of tilting-pad journal bearings with controllable radial oil injection is theoretically investigated, exploring the synergetic effect between passive elastohydrodynamics and active radial lubricant injection.The flexible tilting-pads are modelled as linearly elastic using finite elements. To reduce computational work, a pseudo-modal reduction is applied.Curves of dynamic bearing coefficients as well as the corresponding phase-magnitude plots are presented.Strong synergy between elastohydrodynamics and active control is observed, in particular for bearings with injection orifices far from the pivot line.     

Thermoelastohydrodynamic analysis of the static performance of tilting-pad journal bearings with the Newton–Raphson method

Thermoelastohydrodynamic lubrication (TEHD) analysis is presented to investigate the static performance of tilting-pad journal bearings. A completely numerical solution is obtained. The Newton–Raphson method is employed to predict the bearing characteristics of the hydrodynamic pressure, the eccentricity and the pad attitude angles simultaneously. For the temperature calculation, three-dimensional (3D) energy equations for the fluid under each pad and 3D heat transfer equations for the pads are solved using a sequential sweeping method. The elastic deformation and thermal expansion of each pad are calculated with the 20-node isoparametric finite element method. It is found that the Newton–Raphson method is a smart and efficient method. The results show that the elastic deformation due to the hydrodynamic pressure and the influence of the temperature elevation play an important role in the calculated bearing system.     

Stability of a rigid rotor in turbulent hybrid porous journal bearings

Stability characteristics of hybrid porous journal bearings with a turbulent fluid film have been investigated theoretically following Constantinescu's turbulent lubrication theory. The stability curves have been drawn for different Re, eccentricity ratios, slenderness ratios and bearing speed parameters. In the absence of any experimental data, laminar flow results obtained by this analysis have been compared and found to be in excellent agreement with the previous results. It is observed that turbulence deteriorates the stability of the rotor and for better performance the value of the bearing feeding parameter, β, should be kept small.     

Stability of the rotor supported in gas journal bearings with a chamber feeding system

This paper describes the results of numerical investigations of the stability problem of the rigid symmetrical rotor supported in two externally pressurized gas journal bearings. The bushes of the bearings are mounted on a system of linear springs and viscous dampers. When the stiffness and damping coefficients of these springs and dampers are chosen correctly, it is possible to avoid the self-excited vibrations of the rotor. Such vibrations, which are caused by the phenomenon of a half-synchronic whirl, are the major obstacle to the widespread application of gas bearings. The results of authors numerical experiments have shown that the elastic support of the bearing bushes can be designed as an additional externally pressurized air ring, surrounding the bush. The set of parameters of such a ring is optimal when the bearing has a chamber feeding system.     

Thermal characteristics of misaligned finite journal bearings

Adiabatic analysis of a journal bearing is presented for maximum allowable misalignment with a length: diameter ratio of one. The direction of journal misalignment is allowed to vary up to the axial plane containing the load vector. Reynolds and energy equations are solved simultaneously using finite differences, considering both axial and spiral oil inlet conditions. The results show that bearing behaviour is significantly affected by journal misalignment. It is also noted that thermal effects are more pronounced for bearings with axial rather than spiral oil inlet grooves.     

Dynamic performance of plain gas journal bearings

This paper presents dynamic performance characteristics of plain gas journal bearings. The perturbation formulation suggested by Lund has been modified to obtain stiffness and damping properties. Since rotor bearing axes are never perfectly parallel, the effect of skew has also been considered. Stability studies have been carried out for selected compressibility parameters     

Hybrid journal bearings with particular reference to hole-entry configurations

There is a spectrum of pressure-fed journal bearings ranging from the purely hydrostatic bearing characteristics, ie zero speed operation, to the purely hydrodynamic bearing characteristics which depend completely on speed. Between these two extremes, hybrid bearing characteristics rely on mixed modes of external pressurisation and speed-dependent pressurisation. Large high speed hydrodynamic bearings require the lubricant to be pumped under pressure for temperature control. It is therefore attractive to use this external source of pressure to enhance the start-up performance by reducing wear and improving stability. Hybrid bearings offer the possibility of improving on both the zero-speed characteristics of hydrostatic bearings and on the whole range of speed characteristics of hydrodynamic bearings. It is concluded that hole-entry bearings may be particularly effective when compared with other bearing configurations for good load support and low energy consumption, when used in any of the four modes of operation including: zero-speed hydrostatic mode; high-speed hydrodynamic mode; zero and high-speed hybrid mode; and jacking mode where areas are pressurised for start-up. A modification to the procedure for solving the Reynolds equation is introduced to cope with cavitated regions. The technique presented for solving the bearing pressures and cavitation boundaries is efficient and has relevance to any type of liquid film bearing     

Experimental study of journal bearings with undulating journal surface

A journal bearing test rig was designed and constructed to test the behaviour of journals with wavy surfaces, the circumferential undulations being varied both in amplitude and in number. Results show that wavy journal surfaces may well enhance the load carrying capacity of a bearing. Moreover, surface undulations are shown to move the journal centre locus closer to the load line, ie cause a lower attitude angle. These effects are found to be more pronounced with larger wave amplitudes, and with higher numbers of waves around the journal circumference. In general, friction is found to be reduced with increase in surface wave amplitude.Good agreement is shown to exist between test results and a computer aided analysis conducted by the authors to predict wavy journals performance¹. It has been established that a wavy journal surface may, under certain conditions, display higher load capacity, lower friction and permit safer running of journal than bearings with perfectly smooth surfaces.     

Experimental investigation of hybrid journal bearings

Experimental pressure distribution measurements in hybrid journal bearings are presented and the influence of inertia forces in the recess outlets and pressure generation in the pockets for high rotating speeds are shown. These results are in good agreement with the theoretical results given by an established model.     

Thermoelastic behaviour of journal bearings undergoing seizure

Extensive numerical results are presented for the behaviour of journal bearing undergoing seizure. Included in the results is a sensitivity study performed to investigate the influence of various bearing parameters and operating conditions on the onset of seizure. It is demonstrated that high shaft speeds could lead to a very rapid seizure when the bearing is subjected to dry sliding. The significance of housing flexibility, internal cooling, and heat conduction through the contact between the shaft and bearing are discussed in depth.     

A FEM approach to simulation of tilting-pad thrust bearing assemblies

Finite-element method (FEM) modelling is applied to analysis of the performance of hydrodynamic tilting-pad thrust bearing assemblies. A 3D model of the bearing assembly that includes the bearing pad and shaft is used to assess the influence of operating conditions on bearing parameters such as temperature and oil film distributions across the pads. The model is first applied to the investigation of a spherically pivoted-pad. Through comparison with results from experiments carried out on just such a bearing, good correlation between the model and experimental results is found for maximum oil film temperature, pressure distribution and thickness. The model is then applied to the examination of a bearing having spring-supported babbitt pads. The effect of different oil types on a spring-supported thrust bearing is analysed. Further application of the model to investigate the same spring-supported pad, this time with a resilient surface coating, is discussed.     

Dynamic stiffness and damping coefficients of aerodynamic tilting-pad journal bearings

The dynamic gas–film forces of aerodynamic bearing often can be characterized by eight linear stiffness and damping coefficients. How to theoretically predict these coefficients is a very difficult issue for tilting-pad gas bearing design because of its structural complexity. The current study presents a novel and universal theoretical analysis method for calculating the dynamic stiffness and damping coefficients of aerodynamic tilting-pad bearing. The gas–film pressure within the bearing is expressed in the form of dimensionless compressible gas-lubricated Reynolds equation, which is solved by means of the finite element method. With the assumption that the journal and the pads are disturbed with the same frequency, the dynamic coefficients of tilting-pad gas bearing are computed by using the partial derivative method and the equivalent coefficient method. Finally, the investigations are conducted about the effects of bearing number, perturbation frequency of the journal and the pads, eccentricity ratios, preload and length-to-diameter ratio of the bearing on the dynamic coefficients of aerodynamic tilting-pad journal bearing. The numerical results indicate that the dynamic stiffness and damping coefficients of tilting-pad gas bearing are closely related with these factors. The proposed analytical method provides a valuable means of predicting dynamic performances of tilting-pad gas bearing. The solution can be used for the purpose of prediction of dynamic behavior of the rotor systems supported by aerodynamic tilting-pad bearings.     

Linear stability analysis of hydrodynamic journal bearings under micropolar lubrication

The dynamic characteristics of hydrodynamic journal bearings lubricated with micropolar fluids are presented. The modified Reynolds equation is obtained using the micropolar lubrication theory. Applying the first order perturbation of the film thickness and steady state film pressure, the dynamic characteristics in terms of the components of stiffness and damping coefficients, critical mass parameter and whirl ratio are obtained with respect to the micropolar property for varying eccentricity ratios and slenderness ratios. The results show that micropolar fluid exhibits better stability in comparison with Newtonian fluid.     

Transient response of a journal supported on elastic bearings

By considering the inherent flexibility of the bearing liner, the non-linear dynamic response of a journal bearing system is determined in this study. The transient analysis is presented and the journal centre motion trajectories are plotted for rigid and flexible bearings. Effects of the different parameters such as the eccentricity ratio, and the deformation coefficient etc on non-linear trajectories are reported in this paper. The transient response of the system is also obtained for different values of the normalized journal mass which shows that a rotating system supported in a flexible bearing may have a better performance under dynamic conditions than one supported in rigid bearings.     

Feed pressure flow in plain journal bearings

The purpose of this short technical note is to update the literature on feed pressure flow in plain bearings and to give a summary of suitable equations for predicting such flows. The work is part of a detailed study of feed pressure flow¹.     

Load-carrying capability of water-lubricated ceramic journal bearings

The possibilities of using advanced ceramics in water-lubricated journal bearings were studied by performing tests on journal bearings lubricated with water. The materials studied were two aluminas (Al₂O₃), a zirconia-toughened alumina (ZTA), a partially stabilized zirconia (PSZ), a sintered silicon carbide (SiC), a reaction-bonded silicon carbide (SiSiC) and a β′-sialon. From the present study it can be concluded that water-lubricated journal bearings utilizing silicon carbide against itself offer good performance. Moderate performance can be achieved with an all-alumina sliding pair, provided that the loads remain low and that a high surface quality can be ensured.     

Analysis of hydrodynamic journal bearings having non-Newtonian lubricants

Commercial lubricants, due to the presence of different types of additives, behave like non-Newtonian fluids. The effect of this nonlinear behaviour on the performance characteristics of finite-width journal bearings is investigated using the Eyring model for the shear stress and shear strain rate. the finite element method using Galerkin's technique has been used to solve the momentum equations and the continuity equation in cylindrical coordinates, representing the flow field in the clearance space of a journal bearing system using Newtonian fluids; the non-Newtonian effect is introduced by modifying the viscosity term for the model in each iteration. The results of static performance characteristics for finite-width journal bearings having non-Newtonian lubricants have been obtained.     

Elastohydrodynamic studies of circular journal bearings with non-Newtonian lubricants

A computer-aided study is presented for the static and dynamic performance characteristics of a hydrodynamic journal bearing with a non-Newtonian lubricant. The Navier-Stokes equations in cylindrical coordinates representing the flow field in the clearance space of a journal bearing using Newtonian fluids have been solved by finite element method using Galerkin's technique; the non-Newtonian effect is introduced by modifying the viscosity term for the model in each iteration. Deformation of the bearing shell is obtained by solving the three-dimensional elasticity equations. Using a suitable iterative solution procedure, the converged solutions for the lubricant flow and elastic deformation fields are obtained.     

Performance of finite journal bearings in non-laminar lubrication regime

Fluid dynamic lubrication of journal bearings in a superlaminar regime, ie a transition or turbulent regime, is the subject-matter of this study.Results obtained by solving an appropriately modified Reynolds bidimensional equation have been put in the form of operating diagrams which allow the correct design of journal bearings in real conditions of flow