DESIGN OF TWO-LOBE HYDRODYNAMIC JOURNAL BEARINGS

Abstract

rotating machinery such as turbines, compressors and pumps. The recent trend towards higher speed for increased performance of turbo machinery has aroused considerable interest in the subject of bearing influenced rotor dynamics. A major contribution to this was the development of new and radical bearing designs such as elliptical bearings, multi-lobe bearings etc. Amongst the various types of non-circular hydrodynamic bearings, elliptical or two-lobe bearings are very popular because of their simple structure, relatively low manufacturing cost and superior durability; moreover they have higher load carrying capacity and stability than circular journal bearings. Analysis of hydrodynamic journal bearing with circular cross-section is comparatively simple, but the analysis becomes complicated in case of bearings with non-circular cross-section due to their complex geometry. In this dissertation work, a computer code has been developed using MATLAB to investigate the static and dynamic performance characteristics of two-lobe hydrodynamic journal bearings. The MATLAB program predicts the pressure distribution in the lubricant film and determines the static and dynamic characteristics of two-lobe hydrodynamic journal bearings. The determination of pressure field involves solving the Reynolds equation which governs the pressure distribution in hydrodynamic journal bearings. The Reynolds equation for the flow-field in the clearance space between the bearing lobes and the journal has been solved by Finite difference method. The analysis based on finite difference method is general and can be extended to study the performance characteristics of any multi-lobe journal bearings. The Reynolds boundaries in the lobes of the bearing are computed with the help of an iterative search procedure. Static characteristics such as Load carrying Capacity, side leakage, frictional coefficient etc were determined and compared with the theoretical results existing in the published literature. With the increase in the operating speed the design of hydrodynamic bearings are reaching a limit whereby the steady state performance does not match the performance predicted by the available theories. This is typically encountered when the v bearing operating conditions are in the turbulent regime. With the continuing drive for greater operating speeds for increased efficiency of high performance machines, the application range of the conventional design is also reaching a limit. Recent developments in journal bearing design have addressed both performance and extension of the application range. These efforts have been concentrated on minimizing power loss and reducing oil flow rates, while at the same time decreasing bearing operating temperature which is very important to avoid melting of soft liner and lubricant oxidation. The computer program developed is thus a preliminary step in evaluating the major performance characteristics of two-lobe hydrodynamic journal bearings. Once, these performance parameters are evaluated, further improvement can be done in the performance of two-lobe bearings by optimization of certain parameters and considering several other operating variables in a more general fashion. vi