PERFORMANCE OF A GEOMETRICALLY IMPERFECT TWO-LOBE CFV COMPENSATED HYBRID JOURNAL BEARING LUBRICATED WITH NON-NEWTONIAN LUBRICANTS

Abstract

Journal bearing that operates at high speed encounter instability issues of whirl and whip, Instability might ruin not solely the bearing but can lead to failure of whole machine. Satisfactory dynamic performance characteristics are essential for proper working of bearing. Circular journal bearings encounter the problem of whirl and whip more frequently when speed of the journal exceeds the stability threshold margin. Over the years it has been determined that non-circular bearings enhances the shaft stability and effectively prevents instability issues of whirl and whip. Among the non-circular bearings, elliptical, two-lobe bearing, three-lobe bearing and four-lobe configurations are studied and in depth analysis is completed on these bearing configurations. Externally pressurized fluid-lubricated hybrid journal bearings have received an excellent deal of attention in recent years, primarily because of the reason that they have better bearing performance characteristics such as greater value of minimum fluid film thickness, high fluid film stiffness, better vibration-damping characteristics, smooth relative motion even at low speed, and better static and dynamic performance characteristics at high speed. To enhance the bearing performance various modifications are made in bearing design time to time. The use of non-Newtonian lubricants may result in better bearing functioning. Also use of varied journal having completely different surface profiles will have good impact on the bearing performance. The main objective of the present dissertation work is to evaluate performance of a geometrically imperfect two-lobe CFV (constant flow valve) compensated four-recessed hybrid journal bearing lubricated with non-Newtonian lubricants (cubic shear stress fluid model). In this work, the Reynolds equation is solved using Finite Element numerical technique (FEM) in order to calculate fluid film pressure in bearing clearance space. To calculate equilibrium position of journal centre, Newton-Raphson method is used. The solution procedure for the analysis of CFV compensated four-recessed hybrid journal bearing is transformed into the source code in Fortran 77. The numerically simulated results are presented in the form of static performance characteristics such as bearing flow rate, maximum fluid film pressure and minimum fluid film thickness as well as the dynamic performance characteristics such as fluid film stiffness and damping coefficients and threshold stability speed margin. Thus, this will contribute to predict the realistic bearing performance characteristics and is expected to be useful to the bearing designers