N.S. Rao

Stability characteristics of rough submerged oil elliptical bearings under dynamic load

Abstract This paper discusses the effect of surface roughness on the stability of submerged oil elliptical journal bearings under unidirectional constant and unidirectional periodic load. The non-linear transient simulation, taking the oil film history into account, has been used to predict the threshold of instability. The average flow model of Patir and Cheng (An average flow model for determining effects of three-dimensional roughness on partial hydrodynamic lubrication. Trans. ASME, Journal of Lubrication Technology , 1979, 100 , 12–17) has been used to describe the surface roughness effects. The effect of ellipticity ratio and that of various surface roughness parameters, viz., composite surface roughness, roughness orientation pattern and variance ratio on the stability has been studied.

Steady state performance of finite hydrodynamic porous journal bearings in turbulent regimes

Abstract A theoretical investigation has been conducted of the steady state performance of finite hydrodynamic porous journal bearings in turbulent regimes, following Constantinescus turbulent lubrication theory. A numerical method has been employed to solve the governing differential equations for a wide range of bearing parameters. The effects of turbulence, eccentricity ratio, slenderness ratio, bearing feeding parameter and anisotropy of permeability on the load carrying capacity, friction coefficient and oil flow rate have been investigated. The results are presented in the form of figures and tables which may be useful for the design of such bearings.

Stability of a rigid rotor in turbulent hybrid porous journal bearings

Stability characteristics of hybrid porous journal bearings with a turbulent fluid film have been investigated theoretically following Constantinescus turbulent lubrication theory. The stability curves have been drawn for different Re, eccentricity ratios, slenderness ratios and bearing speed parameters. In the absence of any experimental data, laminar flow results obtained by this analysis have been compared and found to be in excellent agreement with the previous results. It is observed that turbulence deteriorates the stability of the rotor and for better performance the value of the bearing feeding parameter, β, should be kept small.

Dynamic characteristics of gas-lubricated externally pressurized porous bearings with journal rotation II

Abstract The dynamic stiffness and damping coefficients of an externally pressurized porous bearing with journal rotation have been calculated theoretically by assuming one-dimensional flow through the porous wall. A periodic disturbance (displacement) is imposed on the journal around its concentric position and the dynamic pressure distribution is determined by small perturbations of the modified Reynolds equation. Non-dimensional stiffness and damping coefficients for various design conditions are calculated numerically using a digital computer and presented in the form of design charts and tables.

Effect of velocity slip on the performance of aerostatic porous thrust bearings with uniform film thickness

Abstract A steady state solution for aerostatic porous thrust bearings incorporating the effect of velocity slip is obtained. For rectangular thrust bearings with uniform film thickness the effect of velocity slip on the static characteristics is studied making use of the previously available solution based on the conventional adherence (no-slip) condition. Different slip models are compared in order to study their limitations. The effect of slip is to reduce the load capacity and to increase the mass rate of flow in comparison with the values obtained for the no-slip condition.

On the stability of a rigid rotor in turbulent finite hydrodynamic journal bearings

Abstract The stability characteristics of finite journal bearings in turbulent regime were investigated theoretically, following Constantinescus turbulent lubrication theory. Stability curves were drawn for different slenderness ratios for Reynolds numbers up to 50 000. Computed results are compared with published results (H. Hashimoto, S. Wada and J.-I. Ito, J. Tribol. Trans. ASME, 109 (1987) 307). Turbulence causes the stability of the rotor to deteriorate. However, the stability of the rotor improves with a decrease in the L/D ratio of the bearing.

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

Abstract 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.

Steady-State Characteristics of Aerostatic Porous Rectangular Thrust Bearings Incorporating the Effects of Velocity Slip, Anisotropy and Tilt

A generalized solution is presented in order to predict the steady-state performance characteristics of aerostatic porous rectangular thrust bearings of finite pad thickness. The analysis takes into account the Beavers-Joseph criterion for velocity slip at the bearing interface, the anisotropy of the porous material and the tilt of the bearing. Dimensionless load capacity, mass flowrate of the gas and static stiffness are computed numerically for different operating parameters and bearing dimensions and presented in the form of design charts. The effect of slip is to reduce the load capacity and increase the mass rate of flow.

Turbulent hybrid journal bearings with porous bush: a steady state performance

Abstract A theoretical investigation was carried out into the steady state performance of finite hybrid porous journal bearings in turbulent regime, following Constantinescus turbulent lubrication theory. A numerical method was used to solve the governing differential equations for a wide range of bearing parameters. The effects of turbulence, slenderness ratio, speed parameter, H/R and anisotropy of permeability on the load carrying capacity, friction coefficient and oil flow rate were investigated.

Static Axial Characteristics of Aerostatic Annular Porous Thrust Bearings with Tilt

A theoretical analysis is presented to predict the static axial performance characteristics of a porous circular thrust bearing with a central hole for both open and sealed ends, taking into consideration the tilt of the runner pad. The flow in the bearing matrix is considered to be three-dimensional. The governing equations of gas flow through the porous pad and the bearing clearance are solved simultaneously using the finite difference technique to obtain pressure distribution in the bearing clearance. The load capacity, mass rate of flow and static axial stiffness are calculated numerically for various bearing dimensions and supply conditions and presented in graphical form. The bearings with sealed ends have comparatively better load capacity over those with unsealed ends. The effect of tilt is to decrease the load capacity and increase the mass flowrate.