Introduction

Abstract

Hydrodynamic bearings are known as the mechanical components that smoothly support the external loads due to geometry and relative motion of mating surfaces when a thick film of lubricant exists between them. Such bearings find extensive use in high-speed rotating machines as they have low friction, high load capacity, and good damping characteristics. Due to high speed of the rotor, there was the tendency of occurrence of oil whip and oil whirl phenomenon. Formation of oil whip is not desirable because the rotor cannot form a stable wedge and it leads to metal to metal contact between rotor and bearing. Once surface contact exists, the rotor begins to precess, in a reverse direction from the actual rotor rotation direction, using the entire bearing clearance. This condition leads to high friction levels which increase the temperature of lubricating oil. This will overheat the bearing metal, thus causing rapid destruction of the bearing, rotor journal, and machine seals. Fuller (1956) has suggested that the fluid film bearings are probably the most important mechanical components in the recent technological development and are comparable in their significance (as they were used in turbines which ultimately leads to generation of power) to the effect of electricity. The development of fluid film lubrication mechanisms has been observed by Petrov (1883) in Russia and by Tower (1883) in England. In 1886, Reynolds presented his classical analysis of bearing hydrodynamics, which forms the basis of present days’ bearing study. It has been seen in literature that the temperature rise in the oil film is quite high in circular journal bearings since they operate with single active oil film. To overcome the problem of excessive temperature rise, it leads to the development of bearings with non-circular profiles, which operate with more than one active oil film. The feature of operating with more than one active oil film accounts for the superior stiffness, damping, and reduced temperature in the oil film as compared to the circular journal bearings. Almost all the non-circular journal bearing geometries enhance the shaft stability under proper operating conditions. Such non-circular profile bearings will also help in reduced power losses and increase oil flow as compared to an inscribed circular bearing, thus reducing the oil film temperature. Among non-circular journal bearings, the commonly reported in the literature are: offset-halves, two-lobe, elliptical, lemon bore, and three-lobe configurations.