INFLUENCE OF VISCOSITY VARIATION DUE TO PRESSURE ON THE PERFORMANCE OF TWO LOBED HYDROSTATIC/HYBRID JOURNAL BEARINGS

Abstract

Hydrostatic/Hybrid journal bearings are extensively used in machine tool industries and in heavily loaded machines due to their excellent performance characteristics such as higher load carrying capacity at low as well as high speed and higher value of fluid film stiffness/damping coefficients. The bearing also has its own importance in the satisfactory functioning of the machinery in the form of reduction in wear between two parts in relative motion. Hydrostatic/Hybrid journal bearings utilize an external source to supply lubricant into the bearing clearance space. Hybrid journal bearing associates the mechanisms of hydrostatic and hydrodynamic lubrication due to which it has better static and dynamic performance at low as well as high speed. Further, circular journal bearing suffered with journal instability (whip and whirl phenomenon) at higher speed, therefore non-circular bearing has been developed. Two lobe journal bearing is widely used in the industrial machinery system due to its simple geometry and ease in manufacturing. Two lobe journal bearing provides better bearing performance as compared to circular journal bearing. The main objective of the present work is to evaluate the performance of two lobe hybrid journal bearing with consideration of viscosity variation due to pressure. The Reynolds equation is solved by using FEM in order to calculate the fluid film pressure in bearing clearance space and other performance parameters. The numerically simulated results are presented in the form of static performance characteristics such as bearing flow, maximum fluid film pressure and minimum fluid film thickness as well as the dynamic performance characteristics such as fluid film stiffness/damping coefficients and threshold speed margin. Lubricant behaviour have very important aspect in bearing performance as lubricant viscosity changes with temperature, pressure, shear rate, and flow conditions i.e. laminar or turbulent. Viscosity changes due to pressure is not considered in previous studies of two lobe bearing. Therefore, lubricant viscosity variation due to pressure has been taken into consideration. Further, a comparative performance assessment of circular and two lobe hybrid journal bearing has also been performed. The results of present study will be helpful for the bearing designers.