Annular Thrust Bearings Research Articles

The Effect of Rotational Speed on Fluid Compressibility and Gap Pressure of a Partially Porous Aerostatic Thrust Bearing

This study investigated the effect of the spindle speed on pressure distribution in the air gap and the load carrying capacity of a porous aerostatic annular thrust bearing. Based on the finite volume method and the pressure-velocity coupling scheme of the SIMPLE algorithm with the standard k-ε turbulent model, a CFD software was used to solve the Navier-Stokes equations to calculate pressure and velocity of the air flow. The results revealed there were positive pressure zones and vacuum pressure zones in the air gap between the thrust disk and the bearing. Under the same spindle speed, the pressure difference between the positive peak and the negative peak in the case of incompressible air was greater than that in the case of compressible air. The averaged pressure on the surface of the thrust disk with compressible air flow was higher than that with incompressible air flow. So was the load carrying capacity of the bearing, which increased when the spindle rotated faster.

Numerical calculation and experimental verification of static and dynamic characteristics of aerostatic thrust bearings with small feedholes

In this work, aerostatic annular thrust bearings with feedholes of less than 0.05 mm in diameter are considered, and the static and dynamic characteristics of these bearings are investigated experimentally and numerically. In numerical calculations using the finite difference method (FDM), the discharge coefficients of a small feedhole were determined based on computational fluid dynamics (CFD) software and verified experimentally. In addition, the effect of the bearing surface roughness on the bearing characteristics was analyzed experimentally and numerically. It was confirmed that aerostatic thrust bearings with small feedholes could have larger stiffness and damping coefficient than bearings with compound restrictors.

Fundamental Study on Damping Characteristics of Externally Pressurized Porous Gas Bearing. (Analysis of Annular Thrust Bearing with Orifice and Capillary Models).

An externally pressurized porous gas bearing is known to provide high stiffness. Although damping is also important to realize a high-dynamic-stiffness bearing, few studies have been done on the damping characteristics and their relationships to the stiffness and static characteristics of a porous bearing. This paper reports on the analytical investigation of an externally pressurized porous annular thrust gas bearing using the orifice and capillary models from the aspect of improving its damping characteristics. It is found that stiffness and damping are determined only by the static stiffness, the reaction force of gas film and the ratio of squeeze number to the squeeze number at which damping takes an extreme value. It is also found that the damping ratio ζ is determined only by the ratio of squeeze numbers and the ratio of the static stiffness to the reaction force of gas film. Approximated simple formulas representing the relationship between dynamic quantities and static quantities are presented. The validity of the simple formulas is confirmed in a practical range of design parameters by comparison with the results of numerical calculation.

Stability Criterion for Spiral Grooved Thrust Gas Bearings

A previous analysis of dynamic stability for a blocked center inward pumping spiral grooved thrust gas bearing is extended to two other types of similar bearings, namely annular thrust bearings with either inward or outward pumping. Both a numerical small perturbation analysis and an analytical procedure are used, the latter one being based on an approximate shape of the pressure distribution. The analysis provides a critical compressibility number up to which the bearings is unconditionally stable.

Effects of Fluid Inertia Forces on the Performance of a Plane Inclined Sector Pad for an Annular Thrust Bearing Under Laminar Condition

The hydrodynamic wedge of a plane inclined sector pad is analyzed in relation to the lubricant inertia forces under incompressible laminar conditions. Based on the usual assumptions of thin film lubrication theory without the thermal effects, modified Reynolds equations are derived by averaging out all the inertia terms of the Navier-Stokes equations across the film thickness. The equations are linearized with respect to the inertia parameter, and solved numerically for a plane inclined, sectorial configuration. The boundary value of the film pressure at the leading edge is set at the ambient pressure, under the assumption of a negligibly small rampressure thereat. The inertial effects on the static and dynamic performance such as the load carrying capacity, flow rate, frictional torque, position of pressure center, film stiffness, and damping coefficient are discussed, in which the effects of the centrifugal force and those of the other convective inertia forces are compared with each other.

Effects of velocity slip, anisotropy and tilt on the steady state performance of aerostatic porous annular thrust bearings

The analysis predicts the steady state performance characteristics of externally pressurized annular porous gas thrust bearings of finite pad thickness. The modified Reynolds equation, governing the flow in the bearing clearance, is derived from the Navier-Stokes equations using the Beavers-Joseph slip velocity condition at the porous interface. The anisotropy of the porous matrix and the tilt of the bearing are also taken into account. The dimensionless load capacity, the mass rate of flow and the static stiffness are computed numerically and presented in the form of charts for various operating parameters and bearing dimensions. The effect of slip is to reduce the load capacity and to increase the mass rate of flow for all values of the feeding parameter.

Analysis of aerostatic porous annular thrust bearings with tilt

A theoretical analysis is presented in order to predict the static characteristics of an aerostatic porous annular thrust bearing with a tilted runner pad. The flow through the porous matrix is assumed to be axial because the thickness of the pad is small compared with its radius. After the pressure in the porous matrix is obtained, the modified Reynolds equation is solved numerically using a finite-difference technique for the pressure distribution in the bearing clearance. The theoretical results are computed numerically in dimensionless form for the load capacity, mass rate of flow and static stiffness for various bearing dimensions and supply conditions. The results are presented in the form of design charts as a function of the feeding parameter. The effect of tilt is to improve the load capacity and the mass rate of flow.

Pneumatic hammer in a gas lubricated externally pressurised annular thrust bearing : T. B. Stowell, JOLT, Ser F93 (4) (1971) 498–503; 9 figs., 6 refs.

Pneumatic hammer in a gas lubricated externally pressurised annular thrust bearing : T. B. Stowell, JOLT, Ser F93 (4) (1971) 498–503; 9 figs., 6 refs.

Pneumatic Hammer in a Gas Lubricated Externally Pressurized Annular Thrust Bearing

An experimental study was conducted on the occurrence of pneumatic hammer in a gas lubricated externally pressurized annular thrust bearing. The bearing, which was orifice compensated, was fed by sets of three approximately equal orifices having nominal diameters 0.040, 0.020, 0.015, 0.010, and 0.005 in. Instability was most marked for the supply orifices of nominal diameter 0.020 in. The employment of orifices which had nominal diameters greater or smaller than 0.020 in. tended to make the bearing more stable. Experimental results were compared with the predictions of the simple, lumped parameter analysis.

Bearings for the Rotors of a 500-Megajoule Storage Generator

This paper describes the bearings of a homopolar generator which has been built to store 560 × 106 J and capable of discharge at currents up to 1.6 × 106 A. The contra-rotating steel rotors are in a magnetic field which produces a tilting torque of 3 × 109 lb in/rad of tilt, and they must run in either direction at any speed up to 900 rev/min. Conventional bearings and bearing clearances could not be used to restrain the tilt, so annular thrust bearings 92 in in diameter were designed to run on the flat faces of the 139-in diameter rotor discs. Each bearing is supplied with 1500 ft3/min of air at 96 lb/in2. The rotors are centred by hydrostatic bearings lubricated with oil.