A study of misaligned roughened two-lobe hole-entry hybrid journal bearing

Purpose - The non-recessed hybrid journal bearings of cylindrical type, when operating at higher rotational speeds can suffer self-exited vibrations(oil-whirl Instability), which can cause excessive rotor motion causing bearing and sometimes total machine failure. The multi-lobe journal bearing exhibits better stability as well as a superior capability to suppress oil-whirl. The paper aims to present a theoretical study pertaining to a two-lobe hole-entry hybrid journal bearing by considering the combined influence of surface roughness and journal misalignment on the performance of the bearing. Design/methodology/approach - The average Reynolds equation governing the flow of lubricant in the clearance space between the rough bearing surfaces together with the equation of flow through a capillary restrictor has been solved using FEM. The bearing performance characteristics have been simulated for a two-lobe hole-entry hybrid journal bearing for the various values of offset factor, restrictor design parameter, surface roughness parameter, surface pattern parameter and journal misalignment parameters. Findings - The two-lobe hole-entry hybrid journal bearing system with an offset factor greater than one indicates significant improvement of the order of 15-25 percent in the values of direct stiffness and direct damping coefficients compared to a circular hole-entry hybrid journal bearing system. Also the lubricant flow of a two-lobe hole-entry hybrid journal bearing is reduced by 25 percent vis-a-vis circular bearing. Originality/value - The present work is original of its kind, in case of two-lobe hole-entry hybrid journal bearing. The results are quite useful for the bearing designer