A'STUDY ON THE PERFORMANCE OF HOLE-ENTRY HYBRID JOURNAL BEARINGS OPERATING IN TURBULENT REGIME

Abstract

Bearings are used extensively in all rotating machinery in the industry to support load. Their performance plays an important role in chemical, petrochemical, automotive, power generation, aerospace, turbo machinery and process industries. Bearings are generally designed based on empirical relations and design charts. The pioneering work in this field has been done by W. B. Rowe and co-workers. In present time the machines are required to be operated under very stringent, exact and precise conditions so as to cope with the latest technology advancement and constraints. Therefore the bearings are designed on the basis of more accurately predicted design data. Non-recessed hole-entry hybrid journal bearing system, which gives improved performance over recessed hybrid journal bearings, are successfully used in many engineering applications. The non-recessed bearing system especially the hole-entry hybrid journal bearings provide 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 such as reactor coolant pump, liquid rocket engine etc. The phenomenon of turbulence in lubrication has been received increasing attention from many researchers. Turbulence occurs basically for two reasons; high speed operation, and the use of unconventional lubricants of low kinematic viscosity such as water, synthetic lubricants or liquid metals. Sometimes the process fluids of low kinematic 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 generates a turbulent flow. The performance of non-recessed hole-entry hybrid journal bearing systems gets affected by number of parameters such as types of restrictor, mode of operation of bearing and wear. The wear occurs due to frequent (start/stop) operations in 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