EFFECT OF LOAD DIRECTION ON THE ELASTOHYDROSTATIC PERFORMANCE OF MULTIRECESS JOURNAL BEARINGS

Abstract

The hydrostatic/hybrid journal bearing systems have been widely used in number of applications such as rolling mills, machine tools, optical telescopes and medical equipment etc. due their ability support to heavy loads at low speeds, low frictional characteristics and good vibration damping characteristics. The performance of hydrostatic/hybrid journal bearing systems gets affected by number of parameters such as type of restrictor, bearing liner flexibility and mode of operation of bearing (hydrostatic/hybrid) etc. When the journal bearing system is subjected to heavy loads, the bearing liner deforms under high fluid film pressures. This in turn modifies the fluid film thickness profile and ultimately changes the bearing performance. Generally, in recessed bearings there can be two types of load arrangement, i.e one passing through the centre of the pocket and another through the centre of land between the adjacent recess. The similar studies in the case of tilted pad bearings has shown that the bearing performance does get affected due to the alteration of the load direction. Therefore, this work is aimed to study the effect of load direction on the performance of orifice compensated hydrostatic/hybrid journal bearings by taking the flexibility of the bearing shell into account. The performance of multirecess hydrostatic/hybrid journal bearings for two bearing configurations have been compared for the same bearing operating and geometric parameters. The configuration 1 is the journal bearing in which the load line passes through centre of the recess, while in configuration 2, the load line passes through the centre of the interrecess land width. For computing the bearing performance characteristics, the Reynolds equation for the flow of lubricant in the clearance space with equation of flow through restrictor as a constraint has been solved using appropriate boundary conditions. The flow field solution domain has been discretized using 4-noded isoparametric elements. The static performance characteristics are presented in terms of maximum pressure, minimum film thickness, bearing flow and attitude angle. The dynamic performance characteristics are presented in terms of stiffness coefficients, damping coefficients and threshold speed. The effect of load direction on the static and dynamic performance characteristics has been presented in graphical form and conclusions are drawn. The study reveals that the overall decision regarding which configuration is to be used would depend on the design criteria i.e on the basis of stiffness, minimum film thickness and load etc.