Thermal and inertia effects in externally pressurized conical oil bearings

Theoretical and experimental investigations of thermal and inertia effects on the performance of externally pressurized conical bearings are presented. The analysis and the experimental results revealed that the increase in oil temperature due to pad rotation has a detrimental effect on the load-carrying capacity but produces an increased flow rate. Increasing the speed of rotation increases or decreases the bearing load-carrying capacity depending on the recess dimensions.     

Thermal and inertia effects in externally pressurized spherical bearings lubricated with non-newtonian fluids

An analysis of externally pressurized spherical bearings in which the rotational inertia of the lubricant and the variation of the viscosity of the non-newtonian lubricant along the flow are taken into account is presented. A finite difference technique was used to obtain a numerical solution for the pressure and temperature distributions.     

Plane vibration characteristics of multired externally pressurized oil journal bearings

Externally pressurised oil journal bearings are often subjected to dynamic loading and vibration. A theoretical analysis of the dynamic behaviour of orifice compensated bearings is presented and a design procedure outlined. The analysis assumes that the journal undergoes plane harmonic vibration about its mean steady state position in the absence of shaft rotation. The lubricant is assumed to be isovicous and incompressible. Stiffness and damping characteristics are presented.     

Magnetohydrodynamic externally pressurized porous thrust bearings

The characteristics of externally pressurized porous thrust bearings in the presence of a transverse applied magnetic field have been studied. It was found that the load capacity increases as the supply pressure, permeability and strength of the magnetic field increase. The time of approach also increases as the strength of the magnetic field increases for a prescribed porosity parameter.     

Turbulent lubrication of externally pressurized bearings including convective inertia effects

A numerical solution is developed for the equations governing the turbulent lubrication of externally pressurized circular bearings. The eddy viscosity is based on the nonlinear theory proposed by Elrod and Ng. The effects of fluid convective inertia tobether with these of lubricant acceleration at the recess edge are included in the analysis. Typical graphs showing the influence of recess radius ratio, film thickness ratio, pressure ratio, and method of compensation on the bearing performance—pressure distribution, load, flow rate, power consumption, and stiffness—are presented. Inertia effects are shown to increase or decrease the load factor, flow factor, and power factor, depending upon the values of recess radius ratio and film thickness ratio.     

Development of improved externally pressurized gas bearings

As a result of recent research and development work at the K.U. Leuven(Belgium), a number of airbearings with non-parallel airgaps have been designed for which some disadvantages(high costs, low load carrying capacity, small bearing stiffness and sensitivity to pneumatic hammering) have been eliminated or strongly attenuated. The conically shaped airgaps yield a larger thrust force and an increased bearing stiffness. The dynamic behaviour of the air film may be fully characterized as a function of bearing parameters, enabling one to predict the stability limits for a particular application.     

Analysis of externally pressurized gas-lubricated conical bearings

An analysis is presented of externally pressurized conical gas bearings with discrete point pressure sources in the form of orifices located around the circumference at quarter stations from the end of the bearing. The governing Reynolds equation over the developed bearing area is solved by a direct numerical method to determine the pressure distribution. Numerical results are presented in the form of non-dimensional charts for load capacity, flow rate and stiffness for a conical bearing having L/D_M = 1 and semicone angles from 10° to 40°.     

Analysis of orifice compensated externally pressurized gas bearings

Dynamic performance of orifice compensated externally pressurized gas bearings is considered. By adopting the finite element method and modifying the perturbation formulation of Lund, stiffness coefficients, damping coefficients, critical mass and threshold speed for various bearing eccentricities and design parameters have been computed.     

The design of partially grooved externally pressurized bearings

Most hydrostatic and aerostatic bearings are designed using external restrictors in order to obtain sufficient bearing stiffness. Alternatives such as the shallow pocket or partially grooved externally pressurized bearing are seldom applied, in spite of their advantageous constructive simplicity. In this article a simple analytical model to analyze journal bearings with partially grooved surfaces is described. The results of the analytical model are compared to the results obtained by numerical analysis. Both incompressible and compressible fluids are considered. The formulas derived are of extreme simplicity and helpful in finding the groove dimensions for optimal load capability and calculating approximate bearing characteristics using a simple calculator.     

The effects of velocity slip on externally pressurized gas porous thrust bearings

A numerical analysis is presented for the velocity slip on an externally pressurized gas porous bearing consisting of a circular pad with a central partially gas-supplied area and sealed circumferential area. Non-axial flow is assumed in the porous matrix. The modified Beavers-Joseph boundary condition of velocity slip is applied at the interface of the porous matrix and lubricating film. The result shows that the solution with the consideration of velocity slip on porous surface tends to agree with the experimental data for increasingly higher values of bearing number.     

Thermal and inertia effects in externally pressurized conical bearings lubricated with non-newtonian fluids

A finite difference technique was used to derive a numerical solution for the pressure and temperature distributions along the flow through externally pressurized conical bearings lubricated with non-newtonian fluids. The variation in the fluid viscosity with temperature was included in the solution. The effects of the flow behaviour index, the bearing geometry and the bearing speed on the pressure and temperature distributions were investigated under conditions of adiabatic flow.     

Aspects of the performance of externally pressurized journal bearings

The performance of externally pressurized journal bearings with four and six pockets was investigated experimentally. The influences of supply pressure, rotation and restrictor characteristics on the behaviour of the bearings operating under static loading are examined in the light of available theoretical and design information.Load capacities were found to be generally higher with the greater number of pockets but for both bearings the loads supported at given eccentricities are strongly influenced, in some ways unexpectedly, by restrictor non-linearity and the effects of rotation. At low supply pressures the loads are enhanced by increased rotational speeds whereas at high supply pressures the opposite occurs.     

Whirl instability of externally pressurized gas-lubricated porous journal bearings

A study of the whirl instability of externally pressurized gas-lubricated porous journal bearings was made. The theoretical analysis was obtained using a quasi-static assumption. The stability characteristic of a particular journal bearing is given for various supply pressures, design dimensions and feeding parameters. Experimental data confirm the theoretically obtained results.     

Analysis of externally pressurized gas bearings with journal rotation

Theoretical studies of rotating externally pressurized gas bearings with multiple pressure sources have been made. The solution is obtained for finite bearings by using pressure perturbation theory. Theoretical results are compared with experimental data. The theory allows good prediction of bearing load capacity, stiffness and attitude angle.     

Design data for externally pressurised spherical gas bearings

Radial and thrust loading characteristics are given for both single row entry and double row entry bearings. The design data presented gives a basis for comparison of the two bearing configurations. The paper shows that the double entry configuration reduces the negative stiffness regions which occur in single entry bearings. Finally a procedure is given to enable the designer to select a bearing to meet his particular requirements.     

Design of externally pressurized gas bearings for stiffness and damping

A design method for flat, circular thrust bearings is presented in this paper. The design method is based upon a new dynamic model of the bearing and permits the selection of stiffness and damping for applications of bearings in vibrating environments. Application of the design method to the tuning of bearing dynamics is emphasized here, while the development of the dynamic model is discussed in other references. Design constraints are considered in the iterative design procedure and are illustrated in a bearing design example.     

Empirical correlations for the pressure depression in externally pressurized gas bearings

The pressure depression phenomenon, usually observed in the inlet region of externally pressurized gas bearings, is predicated by constructing a simple empirical model. The same sets of experimental data, used previously by other investigators, were used to obtain the empirical equations which formulate the proposed model. Three correlations are proposed. These are the inlet pressure correlation, the minimum pressure correlation, and the position of the minimum pressure within the inlet region. Comparisons between the values obtained using these correlations and available experimental data show good agreement. Further, a comparison between the present model and another previously proposed model shows that the present one gives better results. In addition, comparison between the proposed model and available experimental data shows that the model correctly predicts pressure variations, which occur due to the effect of pressure depression, within the inlet region.     

Tilt stiffness and damping of externally pressurized porous gas journal bearings

The dynamic behaviour of an externally pressurized porous gas journal bearing is analysed by assuming one-dimensional flow through the porous bushing. A periodic disturbance (angular displacement) about the transverse axis is imposed on the bearing and the resulting dynamic pressure distribution is determined by small perturbations of the Reynolds equation. A finite difference method is used to determine the dynamic pressure. Design data for tilt stiffness and damping as a function of squeeze number, feeding parameter, supply pressure and porosity parameter are calculated numerically using a digital computer and are presented in tables and figures.     

Development of externally pressurized small-size conical-shaped gas bearings for micro rotary machines

We have developed externally pressurized small-size conical shaped gas bearings for micro rotary machines such as gas blowers, compressors, and medical devices. The bearings are lightweight and enable machines and devices to be downsized by reducing the number of parts, since the journal and thrust loads can be supported by a pair of bearings. The conical bearings (diameters 8 mm and 10 mm) were designed and the manufacturing techniques were considered. The bearing type is a double-row inherent orifice bearing with four feed holes per row. The shape accuracy of the manufactured bearings is within the design limits, being less than 0.005 mm in both roundness and cylindricity. The surface roughness (arithmetic average roughness) of the parts is 0.0002 mm. The static characteristics were calculated and validated by testing on manufactured bearings. Comparative agreement was obtained between the measured and designed values. The proposed calculation method presents as a relatively simple approach for predicting the bearing characteristics. The test rotor exceeded 350 Hz (21,000 rpm) in the rotational test, and whirl vibration was absent. During testing, the maximum rotor vibration amplitude was 0.0125 mm (corresponding to an eccentricity ratio of 0.89).     

Dynamic behaviour of externally pressurized gas journal bearings with multiple supply holes

A theoretical analysis of the dynamic behaviour of externally pressurized journal bearings using a compressible lubricant is made. Two aspects, (i) “squeeze-film” due to harmonic vibration of a stationary journal and (ii) steady-whirl instability of an unloaded rotating journal were studied. The bearing configuration considered had double plane admission feed holes at quarter station. The effect of recess volume at the downstream of the orifices was considered. The dynamic load and moment were determined for various frequencies, recess volumes and bearing design dimensions. Stability charts of whirl are given for various journal speeds, feed and bearing design parameters.