B.S. Prabhu

Effects of journal misalignment on the performance characteristics of three-lobe bearings

Abstract In this paper an investigation has been made to evaluate experimentally the performance characteristics of a misaligned 3-lobe journal bearing. Various parameters which have been studied are: friction through coast down time analysis, vibration responses, minimum film thickness, stiffness and damping coefficients of the fluid film, system natural frequency and damping factor. The film thickness decreases, friction increases and system damping increases as the bearing misalignment increases.

Analysis of aerodynamic multileaf foil journal bearings

In the present work analysis of a gas lubricated multileaf journal bearing has been presented. The two-dimensional compressible Reynolds equation is solved to establish the pressure field in the clearance space of the bearing. The elastic deformation equation is coupled with the Reynolds equation to get the foil deflections and change in film thickness. The problem has been formulated using the incremental finite element method. The system of equations has been solved using the Newton Raphson iterative procedure. The static performance parameters such as load carrying capacity, frictional torque, minimum film thickness and dynamic characteristics in terms of stiffness and damping coefficients have been presented in a non-dimensional form for various design parameters such as compressibility number, eccentricity ratio, foil stiffness parameter and L/D (length to diameter ratio of the bearing) ratios.

The effect of a non-Newtonian lubricant on piston ring lubrication

Abstract The effect of a non-Newtonian oil (shear thinning) on the lubrication of a piston ring is theoretically investigated. A variation of shear strain rate with shear stress that is cubic in form is used to obtain a modified form of the Reynolds equation (dynamic) applicable to a run-in ring profile which is considered to be a double parabola with a central straight portion. Numerical solutions are obtained for the film thickness, pressure and frictional force over a complete stroke for the case of a constant load. Results presented in non-dimensional form show that the effect of pseudo plasticity is to reduce slightly the minimum film thickness, peak pressure ratio and friction coefficient.

The steady state performance of a hydrodynamic journal bearing with a non-newtonian lubricant

Abstract Using the Reiner-Philippoff shear stress-shear strain rate relation a modified form of Reynolds equation is derived for a non-Newtonian (shear thinning as well as shear thickening) lubricant under conventional hydrodynamic lubrication approximations. A finite difference iteration scheme with successive over-relaxation incorporating Reynolds boundary conditions is used to obtain the pressure distribution of a cylindrical journal bearing. Steady state performance characteristics such as load capacity, friction and flow rate are obtained for various values of non-linear parameters. The results presented in dimensionless form and applicable to shear-thinning as well as shear-thickening lubricants are compared with established results for New-tonian lubricants.

Experimental investigation on the performance characteristics of tilting pad journal bearings for small LD ratios

Abstract In the present paper an experimental investigation has been carried out on the steady state and dynamic performance characteristics of a tilting pad journal bearing. Pad temperature and oil temperature measurements have been made using a thermocouple measuring system. Coast down time experiments were conducted on a rotor bearing test rig, and the coefficient of friction of tilting pad journal bearing has been found out experimentally. The deceleration vs. speed diagrams have been drawn for different length to diameter ( L D ) ratios and ror different loading configurations. Stiffness and damping coefficients have been identified using an identification algorithm and the identified coefficients were compared with the theoretically predicted coefficients.

An experimental investigation of tribological effects on coastdown phenomena in horizontal rotating machinery

Abstract An experimented investigation of the coastdown characteristics of a two-rotor system consisting of a variable-speed d.c. motor driving a flexible rotor on two journal bearings is presented. The characteristics are plotted in terms of decelaration versus speed for various operating conditions (speed, lubricant type, misalignment and commutator carbon brushes). The coast-down curve resembles the classical Stribeck friction diagram and hence can be used to evaluate the transition speed of journal bearings of rotating systems. The results confirm that this simple technique provides a measure of the friction present and indicates the mechanical condition of the rotating assemblies.

Experimental studies of coastdown time

Abstract Coastdown time (CDT) monitoring of power driven rotating systems during every routine stoppage, using the coastdown phenomenon (CDP), is investigated for prediction of onset of failure. CDP plots were made for a variable speed motor with oil, multipurpose grease and Servogem grease lubrication, with released carbon brushes and with various misalignments, each at four cut-off speeds. Results facilitated determination of transition speed by sudden increases and decreases in deceleration on a deceleration versus speed curve of a CDT study. Decrease in CDT after reassembly of the rotating system indicates deviation from correct alignment. Dry friction arising from carbon brushes increases deceleration rate considerably.

The effect of inlet film boundary conditions on the steady state characteristics of hydrodynamic journal bearings

Abstract The well-known solutions for the pressure distribution in the lubricating film of a hydrodynamic journal bearing, satisfying the Reynolds boundary conditions, show a sudden change in the pressure gradient at the position of maximum film thickness, which is possible only if the lubricant is added precisely at this position. Since the pressure develops smoothly because of hydrodynamic action, a correction in the Reynolds boundary conditions is proposed and a new solution for the pressure distribution is obtained. The steady state characteristics of a hydrodynamic journal bearing using the new boundary conditions are compared with the well-known characteristics using the Reynolds boundary conditions.

Conditions for backward whirling motion of a flexible rotor supported on hydrodynamic journal bearings

The necessary conditions for backward whirling motion of a Jeffcott rotor supported in identical hydrodynamic journal bearings are investigated in this paper. Backward whirling motion of the rotor centre is shown to occur if and only if the load parameter is greater than a limiting value corresponding to the flexibility parameter. In spite of the backward whirling motion of the rotor centre, the journal centre is shown to orbit only in the forward sense.

Steady state characteristics of conical hybrid bearings

Abstract The steady state performance of externally pressurized gas-lubricant conical bearings under rotation is presented in this paper. The conical bearing considered had plain orifices around the circumference at quarter stations from the ends of the bearing. The governing Reynolds equation over the developed bearing surface was solved by a numerical method to obtain the pressure distribution. Steady state results are presented in the form of non-dimensional charts for a conical bearing having L D M = 1 and a semicone angle in the range from 10° to 40°. The influence of operating parameters on the radial and axial load capacity, attitude angle, friction loss and stiffness is discussed.