Non-circular Journal Bearings Research Articles

Theoretical and Numerical Investigation of Reduction of Viscous Friction in Circular and Non-Circular Journal Bearings Using Active Lubrication

Reducing friction losses is one of the most common ways to improve fluid film bearings, whose adjustable design provides additional opportunities to improve their dynamic and tribological properties. Previous studies have shown the possibility of reducing viscous friction in actively lubricated bearings by adjusting the rotor position. This work provides a theoretical justification for the mechanism of this effect for the cases of purely laminar lubricant flows in journal bearings. The operating modes connected with the transition to turbulent phenomena and the occurrence of Taylor vortices are beyond the scope of this paper. Conditions that ensure the minimization of friction losses in hydrodynamic and hybrid bearings with hydrostatic parts are determined based on the equations describing viscous friction in a fluid film. In non-adjustable plain hydrodynamic bearings, the minimum of friction is achieved with the centered shaft position that is actually unstable due to the resulting forces configuration. In actively lubricated hybrid bearings, a further reduction in viscous friction is possible by combining film thickness and pressure distributions. Recombining them, along with adjustment of the shaft position, allows the optimization of the distribution of shear stresses in the fluid film. As a result, the shear stresses caused by the rotation of the shaft can be partially compensated by the stresses caused by the pressure gradient, reducing the torque-resisting rotation. In addition, additional benefits can be obtained in the minimum friction state by the reduced lubricant flow and power losses to its pumping. A series of numerical calculations for elliptical, 3-, and 4-lobe bearings show that non-circular bores provide additional variability in film thickness distribution and a premise for optimizing the bearing tribological parameters. Four-lobe bearing demonstrated the best ability for reducing viscous friction among the considered designs. The results obtained can be used as a basis for further optimization of the geometry of fluid film bearings of both active and passive designs by reducing power losses due to viscous friction.

Investigating the steady state characteristics of noncircular journal bearings lubricated with ferrofluid under concentric finite wire magnetic field

The aim of the present work is to investigate the steady state performance of noncircular hydrodynamic two, three and four lobe journal bearings, lubricated with ferrofluid under concentric finite wire magnetic field. Applying momentum and continuity equation, for ferrofluid under the applied magnetic field, modified Reynolds equation is obtained. Assuming linear behaviour for the magnetic material of the ferrofluid, the Reynolds equation is solved, using finite element technique to obtain pressure distribution then applied to study the effect of magnetic lubricant on various bearing performance characteristics such as load capacity, attitude angle, friction coefficient, friction force and side leakage flow. The results indicate with increasing magnetic force coefficient, side leakage in noncircular bearings and friction coefficient is significantly reduced and improvement in load bearing capacity can be seen at the most values of eccentricity ratio, especially in two lobe noncircular bearing. The results also show that the eccentricity ratio has an effective influence on bearing performance characteristics, if the magnetic field and geometric configuration are selected properly.

Effect of texture geometry on the performance of noncircular aerodynamic journal bearings

Today, considerable uses of aerodynamic journal bearings have attracted the attention of many researchers in the field of tribology. Therefore, the theoretical and experimental analysis of their performance has been the subject of many researches. Growing application of the gas journal bearings is due to their capability in various engineering fields such as instrumentation and high-speed machines like spindles, small-scale turbomachines, and precision gyroscopes, dental milling machines, and many other rotor-bearing systems. Upgrading the performance of gas bearings by changing their geometry or using new compressible lubricants has always been one of the suggestions proposed by the tribology researchers. Recently, the development of new technologies such as laser milling and lithography increased the possibility of creating textured surfaces as a way to improve the performance of journal bearings. So, in this study, the effects of texture geometry on the steady-state performance of two-lobe noncircular aerodynamic journal bearings are presented. For this purpose, the governing Reynolds equation of hydrodynamic gas lubrication is analyzed by finite element method according to the changes of the lubricant film thickness in presence of the cubical, cylindrical, and ellipsoidal surface textures. Results show that the creation of textures on the lower lobe compared to the upper lobe or the whole surface is more effective on the performance of two-lobe aerodynamic bearings. Also, increasing both the dimple depth and the amount of bearings noncircularity, especially at shallow texture depth, cause more significant changes in the lubricant film pressure distribution and the bearing performance parameters such as load-carrying capacity, attitude angle, and frictional power loss. Further, it is obvious that the creation of cubical, cylindrical and ellipsoidal textures especially at shallow depth with an increase in the noncircularity of bearings’ geometry have a higher impact on the steady-state performance of the studied rotor-bearing system, respectively.

Control of self-excited rotor disturbances in three-lobe journal bearing space using a couple stress lubricant

In this study, the dynamic behavior of three-lobe noncircular hydrodynamic journal bearings lubricated with couple stress fluid is presented. Currently, application of journal bearings with different geometries such as lobed bearings and using non-Newtonian lubricants, including various additives, are the common suggested solutions by tribology researchers to improve the performance of rotor-journal bearing systems. Due to the incompatibility of new lubricant behaviors including polymer chains or other types of suspended particles with considerable size from the classic Navier–Stokes equations, different models such as couple stress fluid theory have been proposed to evaluate their performance. To investigate the self-excited rotor disturbances caused by various factors, like operating in critical speeds, simultaneous solution of governing Reynolds equation of oil lubricant and the rotor motion equations has been done. The result of dynamic analyses using linear and nonlinear approaches indicates the possibility of enhancing the stiffness and damping ability of the three-lobe bearings by strengthening the couple stress properties of lubricant. It is seen from the results that by increasing the couple stress parameter of oil, the type of rotor perturbations in the bearing clearance space changes from divergent oscillations, as a leading cause of collision between the rotor surface and the bearing shell, to limit cycle motion around the rotor stable position or convergent fluctuations to the static equilibrium point. This improvement in the stability range of three-lobe journal bearings using a couple stress lubricant appears in the results of a linear analysis model in terms of increasing the critical mass parameter and decreasing the whirl frequency ratio. In addition, bifurcation diagram results show that using noncircular three-lobe bearings instead of circular types and replacing the Newtonian lubricant with the couple stress fluid improve the dynamic stability of rotor- bearing supports.

Analysis of Misalignment Effects on Hydrodynamic Non-circular Journal Bearings Using Three-Dimensional Lattice Boltzmann Method

In this paper, a numerical model for prediction of hydrodynamic non-circular journal bearings considering misalignments is proposed. The misalignment effects on non-circular hydrodynamical journal bearings are studied. For analyzing journal’s hydrodynamic film, the LBM method, instead of prevalent CFD methods, has been used; since the LBM method has local behavior, it is suitable for parallelization. Previous numerical and analytical works on this subject have been used for validation, and it is found that the LBM results are reasonably accurate. The simulation for different misalignment factors and preload factors is performed. It is revealed that misalignment can increase the maximum pressure of the bearing up to nearly two times the aligned journal bearing; thus, misalignment is an important parameter in the design and analysis of hydrodynamic journal bearing.

Thermal studies of steadily loaded surface‐textured noncircular journal bearing profiles to investigate the performance characteristics

AbstractThe present research study is carried out to study the performance characteristics of two noncircular journal bearing profiles. Experiments are conducted on a phosphorous bronze hydrodynamic journal bearing test rig to measure the circumferential oil film pressure as well as on the temperature profile at different radial loads and constant rotational speeds to measure bearing performance characteristics, such as oil flow rate, maximum temperature, and pressure. Results reported that noncircular bearings can withstand higher load and minimum power losses than circular bearings. Also, with an increase in the radial load, the oil film pressure and temperature also increased. However, a reduction in negative pressure gradient is reported along the circumference of the lobe resulting in lesser thermal degradation in comparison with the cylindrical bearing.

Influence of thermal pressure and temperature profile approximations in thermohydrodynamic analysis of surface‐textured noncircular journal bearing

AbstractThe present study aims to study the thermohydrodynamic performance of noncircular journal bearings lubricated with multigrade oil. Experimental investigations are carried out on phosphorous bronze hydrodynamic journal bearing with a surface textured at different loading conditions with multigrade oil (MAK 2T oil) as lubricant at different constant rotational speeds (i.e., 1000–4000 rpm) for studying the dynamic characteristics. The journal‐bearing's thermodynamic behavior is analyzed by simplifying modified Reynolds and energy equations to obtain surface‐textured bearing performance characteristics, such as load‐carrying capacity, mass flow rate, and power loss. The noncircular bearings suggest several design parameters, such as a tilt angle for designers. By considering thermal effects for MAK 2T oil lubricant, the requirements of a specific application can be fulfilled.

Dynamic stability analysis of noncircular two-lobe journal bearings with couple stress lubricant regime

In this research, the steady state and dynamic performances of two-lobe noncircular journal bearings with couple stress lubricant are presented. The lubricating oil, containing additives and contaminants, is modeled as the couple stress fluid. The modified Reynolds equation is obtained using the couple stress lubrication theory and is then solved by finite element method as an efficient numerical technique. The steady-state characteristics of bearings, including the load carrying capacity and attitude angle, are determined for various values of the couple stress parameter. The results show that applying the couple stress fluid improves the efficiency of two-lobe bearings in terms of an increased load carrying capacity and reduced attitude angle. Also, the stability performance of the investigated bearings is studied using rotor motion equations based on linear and nonlinear dynamic methods. The results indicate that any increase in the lubricant couple stress parameter enhances the bearing ability to damp the rotor perturbations. In other words, by varying the lubricant from Newtonian oil to the couple stress type and upgrading its properties, the curves of the critical mass parameter and whirl frequency ratio have an increasing and decreasing trend, respectively. Based on the fourth-order Runge–Kutta method results, the dynamic trajectory of the rotor center in the bearing space changes with increasing the couple stress parameter from diverging disturbances and limits the cycle perturbations around the bearing center to converging oscillations to the static equilibrium point. Moreover, the effect of changing lubricant properties on the two-lobe bearing’s performance is more pronounced at higher values of the couple stress parameter, especially with an increase in the noncircularity of bearings’ geometry.

Geometrical analysis of elliptical journal bearings and its effects on friction and load capacity

Elliptical bearings are one type of non-circular journal bearings which has two main advantages over the conventional circular bearings: lower temperature rise and lower vibrations. In this study, the energy equation and Reynolds equation are simultaneously solved under adiabatic boundary conditions. The predicted pressure and temperature are compared to the results of published literature for verification purposes. A parametric study is then conducted on the effect of geometrical parameters of the elliptical journal bearing on the load capacity, friction force, pressure, and oil temperature. Effect of geometric parameters of the bearing on the performance is studied. The results show that non-circularity parameter is the most influential parameter in the bearing, and an increase in the non-circularity results in the decrease in maximum pressure and temperature as well as the friction force. Increasing the eccentricity ratio, on the other hand, will cause an increase in the pressure, temperature, and the friction force. Changes in the angle between the major axis of the bearing and load direction decrease the load-carrying capacity and the non-dimensional pressure and results in an increase in the friction coefficient.

Linear and nonlinear analysis of mount angle effects on the dynamic stability of micropolar lubricated hydrodynamic lobed journal bearings

Journal bearings are one of the most widely used types of supporting devices for industrial machinery, especially for high-speed rotary systems. Considering the importance of mechanical systems ability to control vibrations and motion disturbances, the design of noncircular journal bearings has been one of the appropriate techniques used in recent years. In the present work, the effects of mount angle as a noncircularity unique feature on the dynamic stability of lobed journal bearings with micropolar lubricant are studied. For this purpose, modified Reynolds equation based on the linear and nonlinear methods is solved by generalized differential quadrature (GDQ) method. Then the static and dynamic characteristics of two-, three- and four-lobe bearings including load carrying capacity, whirl frequency ratio, critical mass parameter and rotor perturbation in terms of bifurcation diagram and Poincare map are presented for different values of mount angle. Nonlinear analysis results indicate that variation of mount angle can change the rotor response from limit cycle oscillations to convergent perturbation to static equilibrium point. Further, against plain circular journal bearings, choosing an appropriate orientation or mounting angle provides the optimal stability of noncircular lobed journal bearings. Also, the linear analysis results for the range of dynamic stability are more cautious than the nonlinear method in most of investigated cases.

Thermo-hydrodynamic performance of tilted non-circular micropolar lubricated journal bearings

PurposeThe purpose of this study is to examine the thermo-hydrodynamic performance of tilted non-circular journal bearings lubricated with a micropolar fluid. The investigated bearing types are two- and three-lobe journal bearings with finite length.Design/methodology/approachFor this purpose, modified Reynolds, energy and three-dimensional Laplace equations are solved numerically by using generalized differential quadrature method. The effects of micropolarity characteristics of lubricants, such as characteristic length and coupling number, as well as tilt angle as a design parameter, on the performance of non-circular two- and three-lobe journal bearings are studied.FindingsThe results show that the tilt angle can affect the temperature and pressure profiles causing variation in the performance of non-circular bearings. Increasing coupling number and decreasing characteristic length cause the load-carrying capacity to decrease because of the increase in maximum oil temperature of the fluid film of lubricant and decrease in the minimum oil base viscosity. So, it is possible to select suitable values of tilt angle for achieving optimum performance of these bearings.Originality/valueThe non-circular bearings suggest several design parameters such as tilt angle for designers. By considering thermal effects for micropolar lubricant, the requirements of a specific application can be fulfilled.

A Review on Non-Circular Journal Bearings

A Review on Non-Circular Journal Bearings

Tilt angle effects on the performance of micropolar lubricated noncircular journal bearings

PurposeThe purpose of this paper is to study tilt angle effects as design parameters of noncircular bearings, on the linear dynamic analyses of micropolar lubricated circular, two, three and four lobe journal bearings.Design/methodology/approachReynolds equation in dynamic state is modified considering the micropolarity characteristics of lubricant, and it is solved using generalized differential quadrature method. The perturbed components of the dynamic pressure are extracted based on the linear dynamic model. To explain the transient state of the governing equation, through the linear dynamic approach, the whirling motion of rotor around the steady state position is assumed to be harmonic.FindingsIt is observed from the results that tilt angle has significant effects on the steady state and stability performance of lobed journal bearings. It may be selected suitably to improve the performance of rotor-bearing system, while all other lubricant properties and noncircular bearing design parameters are kept fixed. Results show that among the three types of bearings considered, the dynamic performance of two lobe bearings are more affected by the variation of tilt angle.Originality/valueThe present study is mainly concerned with the effects of tilt angle as a design parameter on the stability performance of a hydrodynamic noncircular journal bearing lubricated with micropolar fluid.

Experimental study for performance evaluation of steadily loaded true elliptical and orthogonally displaced non-circular journal bearing profiles

Purpose The non-circular journal bearings may be used over circular journal bearings because of their superior thermal stability. The paper aims at experimental study of thermal performance of two different true elliptical and orthogonally displaced non-circular journal bearing profiles. Design/methodology/approach The experiments have been conducted on a specially designed test rig which simultaneously evaluates oil film pressure and temperature along the circumference of non-circular journal bearing. The tests are conducted for the designed true elliptical and orthogonally displaced journal bearing at three different rotational speeds of 2,000, 3,000 and 4,000 rpm under the influence of steadily applied load varied from 0.5 to 2.0 kN. The data collected during experimentation have been used to evaluate thermal performance parameters such as maximum pressure, flow rate and effective temperature of the bearings under study. Findings It has been observed experimentally that two lobes of pressure and temperature have been obtained for both the elliptical and orthogonally displaced journal bearing. The negative pressure zone (cavitation area) has been observed to be reduced along the circumference for both the journal bearings which results in less thermal degradation of an oil as compared to circular journal bearing. The oil film pressure and temperature increases with the increase in radial load of both the bearings. The maximum temperature rise of oil film is more in case of elliptical bearing as compared to the orthogonally displaced bearing. Originality/value The experimental data presented in this paper will help the designers to select such kind of non-circular journal bearing for various applications. The designed bearings have resulted in reduced cavitation zone and two positive pressure lobes have been observed which may result in application of such bearings as an alternate for circular journal bearing.

Simulation studies on static thermal behaviour of true elliptical and orthogonally displaced non-circular journal bearing

Purpose The current trend of modern industry is to use machineries which rotate at high speed along with the capability of carrying heavy rotor loads. This paper aims at static thermal analysis of two different profiles of non-circular journal bearings – a true elliptical bearing and orthogonal bearing. Design/methodology/approach The Reynolds equation has been solved through finite difference method to compute the oil film pressure. Parabolic temperature profile approximation technique has been used to solve the energy equation and thus used for computation of various bearing performance characteristics such as thermo-hydrodynamic oil film pressure, temperature, load capacity, Sommerfeld number and power loss characteristics across the bearing. The effect of ellipticity ratio on the bearing performance characteristics has also been obtained for both the elliptical and vertical offset bearing using three different commercially available grades of oil (Hydrol 32, 68 and 100). Findings It has been observed that the thermo-hydrodynamic pressure and temperature rise of the oil film is less in orthogonal bearing as compared to the true elliptical bearing for same operating conditions. The effect of ellipticity ratio of non-circularity on bearing performance parameters have been observed to be less in case of elliptical bearing as compared to orthogonal bearing. It has been concluded that though the rise in oil film temperature is high for true elliptical bearing, but still it should be preferred over orthogonal profile under study, as it has comparably good load-carrying capacity. Originality/value The performance parametric analysis will help the designers to select such kind of non-circular journal bearing for various applications.

A comparative study of the preload effects on the stability performance of noncircular journal bearings using linear and nonlinear dynamic approaches

In this work, the effects of preload factor on the stability performance of noncircular two and three lobe journal bearings with incompressible micropolar lubricant are presented based on the linear and nonlinear dynamic models. Assuming that the rotor is rigid, the governing Reynolds equation for the hydrodynamic lubrication of finite length lobed journal bearings has been modified using micropolar theory. Then, the linear and nonlinear dynamic models which include a certain harmonic disturbance and a time dependent trajectory of rotor center are applied to analyze the stability performance of the considered bearings. The generalized differential quadrature method and fourth-order Runge–Kutta technique have been used to solve the governing Reynolds equation and time-dependent dynamic equations of rotor motion, respectively. Finally, the numerical results for the critical mass parameter and the whirl frequency ratio of the rotor as the stability characteristics of the lobed bearings are obtained for different values of preload factor and are compared together. Results show that the dynamic stability of the noncircular bearings is enhanced by decreasing the preload factor i.e. increasing the amount of bearing noncircularity. These enhancements are in terms of increase of the critical mass parameter and decrease for the whirl frequency ratio. Also, by comparing the two dynamic analysis methods, it is seen that the results of linear model are more conservative in different investigated cases. The results of nonlinear analysis reveal that by changing the preload factor the dynamic responses of the lobed bearings appear in different manners. From the responses, it is observed that the type of dynamic trajectory of rotor center varies from stable fixed point to limit cycle periodic motions and also contact between rotor and bearing’s shell.

Performance comparison of circular, two-lobe and elliptical journal bearings based on TEHD analysis

Purpose – The purpose of this paper is to study the different performance of circular, two-lobe and elliptical journal bearings by TEHD analysis. Design/methodology/approach – A complete 3D TEHD model of journal bearings is set up and applied to the lubricant performance calculation of the conventional circular, two-lobe and elliptical journal bearings. The finite difference method is employed to solve the THD model, and the thermo-elasto deformations on the pad are obtained by the finite element software ANSYS11.0. The data transfer between the THD model and ANSYS11.0 is carried out automatically by Interface Program. Findings – It is found that under the identical geometric parameters and operating condition, the circular journal bearing possesses the greatest magnitude of the maximum oil film pressure, the two-lobe one takes the second place and the elliptical one possesses the smallest magnitude. The thermo-elasto deformations on the pad is the same order of magnitude with the minimum film thickness. Practical implications – A complete 3D TEHD model made up of the THD model and ANSYS11.0 can be applied on journal bearings in practice applications. Originality/value – This paper set up a complete 3D TEHD model that is in common use for the lubricant performance analysis of circular and non-circular journal bearings.

Preload effect on nonlinear dynamic behavior of a rigid rotor supported by noncircular gas-lubricated journal bearing systems

This paper presents the effect of preload, as one of the design parameters, on nonlinear dynamic behavior of a rigid rotor supported by gas-lubricated noncircular journal bearings. A finite element method has been employed to solve the Reynolds equation in static and dynamical states and the dynamical equations are solved using the Runge–Kutta method. To analyze the behavior of the rotor center in horizontal and vertical directions under different operating conditions, dynamic trajectory, power spectra, Poincare maps, and bifurcation diagrams are used. Results of this study reveal how the complex dynamic behavior of two types of noncircular bearing systems comprising periodic, KT-periodic, and quasi-periodic responses of the rotor center varies with changes in preload value.

Effect of bearing number on non-linear dynamic behaviour of aerodynamic non-circular journal bearing systems

The present article presents the effect of bearing number on non-linear dynamic behaviour of a rigid rotor supported by aerodynamic non-circular journal bearings. A finite-element method has been employed to solve the Reynolds equation in static and dynamical states and the dynamical equations are solved using the Runge-Kutta method. To analyse the behaviour of the rotor centre in the horizontal and vertical directions under different operating conditions, dynamic trajectory, power spectra, Poincare maps, and bifurcation diagrams are used. The results of this study reveal how the complex dynamic behaviour of these three types of non-circular bearing systems comprising periodic and KT-periodic responses of the rotor centre varies with changes in bearing number values.

Study on Improvement of Stability of Noncircular Journal Bearings(Stability Analysis for Various Bearing Orientation Angles)

Noncircular journal bearings, such as multi-lobe, offset, stepped bearings are used widely for supporting the high speed rotating machinery because of their advantages of relatively low manufacturing costs, stability, load carrying capacity and durability as compared with fullcircular bearings. The stability of noncircular journal bearings are influenced by many bearing parameters such as clearance, preload factor, length-to-diameter ratio, feed hole location etc. However, it is not clear the effects of bearing orientation angle, which is equivalent to the location of applied load line, on the stability of hearings. In this study, the effects of bearing orientation angle on the stability of rotating shaft supported symmetrically by the noncircular bearings are examined theoretically.