Non-circular Bearings Research Articles

Performance Characteristics of Cavitated Noncircular Journal Bearings in the Turbulent Flow Regime

In this paper, the characteristics of noncircular bearings, considering the effects of turbulence and cavitation, are numerically analyzed. Four bearing profiles are considered: circular, worn-circular, two-lobe and elliptical. To model the turbulence, the linearized lubrication theory of Ng and Pan is used. Reynolds' equation is suitably modified to account for both turbulence and cavitation. The equation is incorporated into the Elrod cavitation algorithm. This numerical procedure, which conserves mass throughout the bearing, implicitly incorporates the JFO boundary conditions at rupture and reformation boundaries. JFO theory is considered to accurately model cavitation in moderately to heavily loaded bearings. Performance predictions are compared to results presented in a variety of earlier papers.

A study on stability characteristics of externally pressurized noncircular air-lubricated journal bearings.

An experimental study is performed for investigating the threshold of whirl instability of the rigid rotor supported by two externally pressurized air-lubricated journal bearings. Three types of bearings, that is, 3-lobe, 4-iobe and circular bearing s, of 40 mm diameter and 40 mm length are tested. The rotor rotates horizontally and air supply pressure varies from 0.098 MPa to 0.49 MPa. The effect of supply pressure and radial load, which is applied to the rotor by means of an electromagnet, from 8.1 IN to 32.6 IN with constant rotor mass on the threshold of whirl instability are discussed. It is shown that the noncircular bearing is effective for the prevention of whirl instability.

Stability analysis of orthogonally displaced bearings

Journal bearings operating at high speeds often exhibit vibrational instability. Circular bearings are known to be prone to vibrations and, in general, a non-circular bearing geometry enhances shaft stability. Among the several possible configurations of non-circular bearings, elliptical, offset, three-lobe and tilted three-lobe bearings have attracted attention. The present analysis is a theoretical prediction of stability for a hybrid two-lobe bearing obtained by displacing the lobe centres of an elliptical bearing. It has been found that an orthogonally displaced bearing is more stable than the hitherto known bearings and at the same time it is easier to manufacture. Numerical results have been presented for nine combinations of horizontal and vertical displacements of lobes and three L D ratios so that a suitable profile and L D ratio can be selected by a designer in a specific application.

A Boundary Integral Equation Method for the Study of Slow Flow in Bearings With Arbitrary Geometries

This paper investigates the steady slow flow of an incompressible viscous fluid in the region between an inner circular cylinder rotating with constant angular velocity and an outer stationary cylinder of arbitrary cross section. The numerical solution technique known as the boundary integral equation method is employed in which the governing partial differential equations of motion are recast into coupled integral equations by repeated applications of the divergence theorem. The method is applied to the two dimensional flow within the eccentric journal bearing, and it is found that certain aspects of previous analytic treatments of this bearing have been in error. An extension of the method is applied to solve for the flow within an elliptical bearing, for which no analytic solution or numerical results are available. This extension is able to solve for the flow within any bearing geometry, however complex. It is found that the present method is particularly suited to the prediction of flow separation within noncircular bearings, and it is hoped that these results and techniques will lead to a better understanding of the conditions causing the phenomenon of cavitation.

Developments in engine bearing design

Some of the important recent developments in engine bearing design techniques are highlighted. The availability of increased computing power has enabled more realistic assumptions about bearing conditions to be considered; these include oil feed features, oil film history, non-circular bearings, inertia effects due to journal centre movement, improved prediction of main bearing loads, flexible housings and special bearings. References to these advances are made, together with illustrations of how they affect predicted bearing performance. Experimental evidence is also being obtained, which helps to verify and give confidence in the analytical predictions

Analysis of non-circular gas bearings including skewed axes

The steady state performance characteristics of non-circular gas bearings with journal bearing axes parallel and skewed are presented. The incremental finite element formulation suggested by Reddi and Chu was extended to obtain results for elliptical and three-lobe bearings. The validity of the method was checked with the results obtained by Pinkus.

Performance Characteristics of Noncircular Bearings in Laminar and Turbulent Flow Regimes

Using linearized turbulent lubrication theory of Ng and Pan, the modified Reynolds equation has been solved by finite element method using Galerkin's technique. Static and dynamic performance characteristics of the noncircular (two-lobe) bearings have been studied, both for laminar and turbulent flow, in terms of load support, oil flow, fluid film stiffness coefficients, damping coefficients, and critical mass for various Reynolds numbers.

Performance Characteristics of Two-Lobe Hydrodynamic Journal Bearings

The performance characteristics of noncircular bearings are known to be superior to those of the circular bearings. The two lobe bearings are finding increasing application in high speed turbomachinery. Using a variational solution, detailed design data have been computed for two-lobe bearings in this paper. The data include Sommerfeld number, equilibrium locus, fluid film stiffness and damping coefficients, end-flow, friction parameter, and temperature rise parameter.

A variational solution of two lobe bearings

Non-circular bearings are finding extensive use in high speed machinery as they enhance shaft stability, reduce power losses and increase oil flow (as compared to circular bearings), thus reducing bearing temperatures. Elliptical bearings are among the commonly used non-circular bearings. In this paper, a solution using a variational approach has been presented to analyse elliptical bearings. The results of an elliptical bearing actually in use in a 110 mW turbo-set have been compiled.

The Influence of Oil Lubricated Journal Bearings on the Dynamics of Rotating Systems

SYNOPSIS A computer program representing a shaft and rotor whirling in bearings which allows for realistic oil film boundary conditions and non-circular bearing profiles has been developed. It gave good agreement with experimental results published by Brown and France. With the aim of increasing understanding of the influence of bearing profile on system instability, the program calculates the timewise variation of the energy in translational motion supplied to the rotor by oil film forces. One case is illustrated.