INFLUENCE OF WEAR ON THE PERFORMANCE OF SLOT-ENTRY JOURNAL BEARINGS OPERATING IN TURBULENT REGIME

Abstract

The growing demands from industries for higher speed applications and ability of hybrid journal bearing to support heavy loads at very high speed have necessitated to study the performance of bearings in detail under more realistic conditions. Non-recessed slot-entry hybrid journal bearing system, which gives the improved performance over recessed hybrid journal bearings, are successfully used in many engineering applications. The non-recessed bearing system especially the slot-entry hybrid journal bearings provide the excellent performance such as low power consumption, increased minimum fluid film thickness, large fluid film damping and relatively simplicity in manufacturing. These features make these bearings more suitable for many engineering applications. The phenomenon of turbulence in the lubrication has been received increasing attention from many researchers. Turbulent flow occurs in bearing flow basically for two reasons; high speed operation, and the use of unconventional lubricants of low kinematic viscosity such as synthetic lubricants, water or liquid metals. Sometimes, process fluids of low viscosity are used. as lubricants to simplify the equipment design or to overcome the difficulty of shaft sealing. A high velocity combined with low kinematic viscosity leads to high Reynolds number resulting in turbulence flow. The performance of non-recessed slot-entry hybrid journal bearing system gets affected by number parameters such as slot width ratio, mode of operation of bearing and wear depth. The wear occurs due to frequent start/stop operations in hybrid journal bearings. During the transient periods, the bush progressively wears. The wear could be large and may significantly alter the bearing performance depending upon bearing material and applied load. Therefore, the influence of wear on the performance of bearing characteristics is quite significantly. The aim of present work is to analyze the influence of wear on the performance of slot-entry journal bearings operating in turbulent regime. For computing the bearing performance characteristics, the wear caused on the bearing surface is modeled using Dufranes's abrasive wear model. The modified Reynolds equation based on Constantinescu's lubrication theory has been solved using FEM. The numerically computed results have been presented for bearing operating and geometric parameters, for iii various values of Reynolds number and conclusion has been drawn for non-recessed slot-entry hybrid journal bearing system. The computed results suggest that it is imperative to account for the effect of wear in order to predict the performance of bearing operating in turbulent regime accurately. It has been observed that the value of hmin reduces as the value of wear depth parameter increases. However, due to combined influence of wear and turbulence the value of hmin gets enhanced. Further slot width ratio = 0.25 has the higher value of h„l~n compared to slot width ratio = 0.5 and 0.75 configuration. In general it is observed that, wear in bearings decreases the performance of bearing when operating in turbulent regime. iv