Plain Cylindrical Journal Bearings Research Articles

Numerical analysis of three lobe hydrodynamic journal bearing using CFD–FSI technique based on response surface evaluation

This work is continuation of the earlier work published on an analysis of plain cylindrical journal bearing using CFD–FSI technique. Here, the technique is applied to analyse three lobe journal bearing. The numerical simulations were carried out using ANSYS Workbench® software. The hydrodynamic pressures were computed using computational fluid dynamics (CFD), and structural deformations were estimated using structural module. The fluid pressure forces and displacements were transferred via inbuilt transfer interface available in the software. The optimization of the journal bearing position was carried out based on response surface optimization. The numerical results were compared with experimental results which were available in the literature, and a good agreement was found. The proposed numerical method was implemented to study the pressure distribution in three lobe journal bearing considered for study at three eccentricity ratios 0.25, 0.6 and 0.75 for various speeds ranging from 1000 to 4000 RPM in order to study effect of eccentricity ratio and speed on static pressure distribution in the bearing. Preload factor of 0.5 was considered for the study. The results were compared with a set of experimental data obtained on a test rig developed by the authors. The uncertainty analysis of the experimental results was also carried out, and all the results were found in expected range of pressure.

Dynamic Characteristics of a Finite-Width Journal Bearing Lubricated with Powders

This paper attempts to investigate the dynamic characteristics of a powder lubricated journal bearing. The stiffness and damping coefficients are obtained using finite perturbation method. The stability limit of the rotor speed is obtained for a system consisting of a single rotor disc in the middle of a flexible shaft having identical plain cylindrical journal bearings at the ends. The threshold speed of instability for a rotor supported on powder lubricated journal bearing is compared with that of oil lubricated journal bearing. The numerical results show that a rotor supported on powder lubricated journal bearings remains stable for a speed limit much higher than that for oil lubricated bearings.

Effect of Axial Groove on Steady State and Stability Characteristics of Finite Two-Lobe Hybrid Journal Bearing

The study of the steady state and stability characteristics including whirl instability of finite two-lobe hybrid journal bearing with an axial groove, located at the top from which oil is supplied at a constant pressure is obtained theoretically. The two lobes of 1600 arc each are separated by two axial oil groove of 20° circumferential extensions in the horizontal direction. A two-dimensional finite difference solution was used to predict the performance of finite length externally pressurized two-lobe hydrodynamic hybrid journal bearings.The Reynolds equation is solved numerically using finite difference method satisfying the appropriate boundary conditions to obtain the effect of speed parameter on bearing performance.The stability characteristics were found out using first-order perturbation method. With the change of speed Stiffness and damping coefficients behaviour was determined at various eccentricity ratios. The bearing load-carrying capacity, stiffness, lubricant flow rate, attitude angle and frictional torque due to bearing rotation increase with increase in eccentricity ratio and speed. A comparison is also made with plain cylindrical axial grooved journal bearing. It is found that externally pressurized two-lobe hybrid bearing is more superior to plain cylindrical axial-grooved oil journal bearing in terms of load capacity, improved end flow, friction losses and stability. The bearing is generally stable at high values of the eccentricity ratio and speed parameter.

A Comparative Performance Analysis of Gas Lubricated Cylindrical and Elliptical Journal Bearings

The finite element method is employed to perform a comparative analysis of gas lubricated cylindrical and elliptical journal bearings in this work. A finite element procedure, based on the Galerkin weighted residual method, is specially devised to solve the zeroth- and first-order lubrication equations for plain cylindrical and non-cylindrical hydrodynamic journal bearings running on thin gas fluid films. Load-carrying capacity and dynamic force coefficients of gas cylindrical and elliptical journal bearings are computed for some geometric and operating parameters, such as journal eccentricity ratio and rotational speed. Several comparative curves of steady-state and dynamic bearing characteristics depict the differences in the behavior of some gas lubricated fixed-geometry journal bearings.

Evolution of the lubrication regime of a cylindrical journal bearing in the starting phase

Purpose – The paper aims to analyze the evolution of the lubrication regime by studying the variation of friction coefficient with the rotational speed of the shaft and the impact of the applied load in the starting phase of a cylindrical journal bearing. The paper also aims to ensure that the oil layer is large enough for the rough edges of the outer layer of the bushing and the shaft cannot come into contact. The bearing is made of steel backing material and babbitted (88 per cent tin) on its inner surface. Design/methodology/approach – A numerical analysis is performed taking into account the thermal effect to better predict the operating performance of a hydrodynamic plain cylindrical journal bearing during the start-up and observe the variation of the heat production in bushing inner surface. The flow is modeled based on the Reynolds equation and discretized using the finite volume method. Findings – The evolutions of the start-up speeds of the bearing have remarkable influence on friction torque; average temperature and dissipated power increased with increasing speed and increasing load, but the maximum pressure and the eccentricity decreased with the increase of the start-up speed. The friction coefficient, minimum film thickness and attitude angle increase with elevation of start-up speed. Originality/value – For the start-up speed of 750, 1,000 and 1,800 rpm and an applied load of 1,000 N, the regime of lubrication of the bearing passes the hydrodynamic regime to the mixed regime; therefore, during start-up and under heavy loads, the bearing must move very quickly at these speeds to avoid contact of the inner surface of the bearing and the shaft.

Investigation of Stress State and Contact Pressures in Contact Area of Journal Bearing by Numerical Simulation

Goal of the paper was to investigate stress state and contact pressures in contact pair of tribological assembly by numerical simulation. This paper deals with simulation of cylindrical contact pair. One part has convex (shaft) and other one concave (hole) surface of the body. This assembly represents friction state of the plain cylindrical journal bearing. The paper includes results of stress state and contact pressures from two loading states. The first loading state includes only radial loading without effect of the torque moment and the second one includes radial loading with torque moment. If we want to know more about tribological processes we will have to know stress state in the materials loaded through contact interaction between two bodies to the last detail. This level of knowledge can be achieved just by numerical simulation. The simulation was made by CAE system ANSYS.

Multi-objective optimisation of support characteristics of rotor bearing systems

Rotors today are made highly flexible with ever increasing demand for higher speeds, and it is important to predict the rotor dynamic behaviour accurately. Supports play an important role and influence the magnitude of vibration in response to external forces. In the present study, frequency dependent polymeric support characteristics have been found by using a multi objective optimisation scheme for minimising the unbalanced response and maximising the stability limit speed. This is an improvement over the previous papers where a simple equally weighted sum of two objective functions was used. A novel hybrid of particle swarm optimisation (PSO) and augmented Lagrangian has been used here to find the global minima. Using appropriate constraints, the slope of the support characteristics versus frequency is restricted to realistic values. Rotor systems with rolling element bearings and plain cylindrical journal bearings are studied using this approach and higher stability limits are obtained.

Some Experiments on Oil Whirl and Oil Whip

The oil whirl and oil whip phenomena have been well known since the early twentieth century. However, there is a lot of confusion on the parameters that affect the onset of instability. In this study, we investigate the onset of instability on a flexible rotor mounted on two plain cylindrical journal bearings. The rotor is run through the first critical speed, the instability, and the second critical speed. Tests are conducted at various unbalance levels, pressures, and misalignment conditions on the coupling. It is shown that, by far, the misalignment of the coupling is the parameter that is most effective on the onset of instability. In particular angular misalignment resulted in the smoothest rotor response.

Linear Stability Analysis for a Hydrodynamic Journal Bearing Considering Cavitation Effects

The purpose of this paper is to present the two-dimensional linear stability analysis considering the fluid flow in both full film and cavitation regions for a plain cylindrical journal bearing. The Lund's infinitesimal perturbation procedure is applied to Elrod's universal equation for evaluation of unsteady pressure gradients. Based on JFO theory, the pressure distribution, film rupture, and reformation boundaries can be obtained using Elrod's universal equation, for a given operating position of the journal. In this work, it is assumed that for infinitesimal perturbation of a journal about the equilibrium position, the film rupture and film reformation boundaries are the same as those obtained for steady state. However, the unsteady pressure gradients in the full film region are evaluated taking into consideration the perturbed flow parameters in the cavitation region, i.e., at both rupture and reformation boundaries. The linearized stiffness and damping coefficients, whirl frequency ratio, and threshold speed for various values of eccentricity and L/D ratios are obtained for a plain cylindrical journal bearing with an axial groove along the load line. Measured data of dynamic coefficients for a 120° partial arc bearing are chosen for comparison with this work. Results show good agreement between the theoretical and experimental results. Presented at the 57th Annual Meeting in Houston, Texas May 19–23, 2002

DESIGN OF OPTIMUM SUPPORT PARAMETERS FOR MINIMUM ROTOR RESPONSE AND MAXIMUM STABILITY LIMIT

Viscoelastic polymeric materials provide good support elements to rotor shaft systems by virtue of their efficiency in dissipating vibratory energy. The in-phase stiffness and loss factor for such materials also change with the frequency of excitation they are subjected to. In this paper frequency dependent characteristics of the polymeric supports have been found by simultaneously minimizing the unbalanced response and maximizing the stability limit speed. This process yields better support characteristics than those obtained by minimizing unbalance response alone. Optimum characteristics have been found for the rotor shaft system mounted on (a) rolling element bearings and (b) plain cylindrical journal bearings at the ends having polymeric supports. The effects of viscous internal damping in the shaft, support mass and gyroscopic effect due to non-symmetrical location of the disc have been considered in the analysis. A procedure of controlling the slope of the support characteristics versus frequency of excitation has been used and found to be very suitable for obtaining feasible support characteristics. Examples have been presented to justify the above conclusions.

Oil flow in plain steadily loaded journal bearings: Realistic predictions using rapid techniques

The aim of the paper is to produce a rapid calculation method for predicting lubricant flow in plain cylindrical journal bearings. Lubricant flow data, already available from rigorous solutions considering the effect of film reformation, are used together with experimental evidence to develop unique graphical aids and flow prediction equations. These equations, although developed from specific flow data, are of a general form and therefore will be applicable to a wide range of different bearing operating conditions. Graphical aids, from which the flow equations are derived, give normalized actual flow as a function of normalized hydrodynamic flow for different groove geometries. The main input parameters, namely a hydrodynamic flow term Qh and a feed pressure flow term Qp, are easy to derive and have been in common use in bearing design techniques over many decades. The new design aids, in chart and equation form, give realistic flow predictions for bearings with an oil hole, a groove opposite the load line, an axial groove at the maximum film thickness position and the commonly used case of a bearing with two axial grooves. The flow prediction equations are supported by experimental data.

Stability characteristics of rotating systems with journal bearings on viscoelastic support

An analysis for determining the stability limit of the rotor speed of a rotor shaft system, is given. The system consists of a single rotor disc in the middle of an elastic shaft having identical plain cylindrical journal bearings at the ends, supported on viscoelastic supports. The influence of support parameters on the stability limits of the rotor shaft system has been studied.

Fast Numerical Approach for Analyzing Self-Acting Gas-Lubricated Bearings Using a Multigrid Method.

A multigrid method has been introduced as a fast alternative to conventional relaxation methods for obtaining a solution to the Reynolds equation for self-acting gas-lubricated bearings. This paper verifies the procedure applied to both static and time-dependent dynamic analyses of plain-cylindrical journal bearings. The method gives successful results with less computational effort compared with single grid-oriented iterative methods. In addition, the new approach does not require a trial and error process to optimize the overrelaxation parameter unlike a successive overrelaxation method. The nonlinear orbit method which is an accurate but time-consuming transient analysis is expected to be reduced to a handy design tool for a complicated bearing system on incorporating the multigrid technique.

An Experimental Investigation of Pressure Distributions in a Journal Bearing Operating in the Transition Regime

Experimental results are presented, relating to friction factors and circumferential pressure distributions, for a plain cylindrical journal bearing with a central circumferential inlet groove. The length-diameter ratio of each journal bearing land was 0.25 and the clearance ratio was 0.0031. The friction factor results showed the existence of a distinct ‘transition regime’, characterized by a pronounced ‘hump’ in the friction factor-Reynolds number relationship. Pressure measurements recorded when operating in this transition regime revealed the inadequacy of many existing ‘turbulent’ theories for superlaminar lubrication. By using a short-bearing theory a good correlation of the pressure distribution results was obtained, in terms of a non-dimensional viscosity parameter, kz, which is dependent on both the eccentricity ratio and Reynolds number. The magnitude of kz in this regime was considerably higher than the corresponding value for laminar flow, and was similar to the magnitude predicted from a simple theory based on relating kz to the variation of measured friction factor with Reynolds number.

Bifurcation Theory Applied to Oil Whirl in Plain Cylindrical Journal Bearings

An analysis of the self-excited oscillations of a rotor supported in fluid film journal bearings is presented. It is shown that Hopf bifurcation theory may be used to investigate small-amplitude periodic solutions of the nonlinear equations of motion for rotor speeds close to the speed at which the steady-state equilibrium position becomes unstable. A numerical investigation supports the findings of the analytic work.

Stability of Unsymmetrical Rigid Rotor Supported by Self-Acting Gas-Lubricated Journal Bearings

In order to determine the threshold of instability for an unsymmetrical rigid rotor supported by two identical self-acting, plain-cylindrical gas journal bearings, a theoretical approach is made by the use of the quasi-static nonliner PH method. Influence of various parameters affecting the threshold of instability of the unsymmetrical rotor is experimentally shown and compared with the theoretical results. The experimental variables considered in this paper include bearing load, bearing length, bearing clearance, the axial deviation of the center of gravity from the center of the rotor span. Good agreement was obtained between the experimental and theoretical results.

The influence of non-newtonian oil film short journal bearings on the stability of a rigid rotor

The stability behaviour of rotors supported in plain cylindrical cavitated non-Newtonian fluid film journal bearings is investigated. Expressions for the journal force due to the fluid film are developed for the short bearing approximate solution to the modified form of Reynolds' equation. Linearised fluid film coefficients are used for the stability analysis. The results show that the dynamic fluid film coefficients for non-Newtonian lubricants are different from Newtonian coefficients and that they have a strong influence on the stability of rotor-bearing systems.

Analysis of plain cylindrical journal bearings in turbulent regime : E. B. Arwas, B. Sternlicht and R. J. Wernick, J. Basic Eng., 2 (1964) 387–395 ( Trans. ASME, 86D). For abstract see Appl. Mech. Rev., 18 (3) (1965) 254

Analysis of plain cylindrical journal bearings in turbulent regime : E. B. Arwas, B. Sternlicht and R. J. Wernick, J. Basic Eng., 2 (1964) 387–395 ( Trans. ASME, 86D). For abstract see Appl. Mech. Rev., 18 (3) (1965) 254

Paper 22: The Onset and Cessation of Half-Speed Whirl in Air-Lubricated Self-Pressurized Journal Bearings

The experimental work reported in this paper has shown that it is possible to proceed into and beyond the half-speed whirl region and operate at much higher speeds without vibration, using plain cylindrical journal bearings. Journals of 1-in diameter, clearance ratios greater than 1 in 1000, and bushes with length-diameter ratio of 1 were used. The bushes were mounted flexibly in rubber O-rings.

Stability Analysis of Gas-Lubricated, Self-Acting, Plain, Cylindrical, Journal Bearings of Finite Length, Using Galerkin’s Method

This paper extends the method of Cheng and Trumpler [5] to study stability of plain cylindrical gas journal bearings of finite length. Both equilibrium and stability results have been obtained.