COMBINED INFLUENCE OF HOl.fik3lZf AND JOURNAL MISALIGNMENT ON THE PERFORMANCE OF HOLE- ENTRY HYBRID JOUftNAI. BEARING

Abstract

It is quite usual in the manufacturing of hole-entry hybrid journal bearing, to form small holes at the bearing restrictors. The size and number of these holes directly affects the bearing performance. Also, the journal misalignment due to the under mentioned reasons greatly affects the bearing performance. The journal misalignment in hole-entry hybrid journal bearing is mainly caused by non-central loading, a moment produced by couple forces on the journal, shaft deflections due to elastic a thermal distortions and assembly errors. This journal misalignment modifies the fluid film thickness in both circumferential and axial directions of the bearing. Thus the bearing performance characteristic gets affected due to the hole size and journal misalignment. Therefore, the analyses based upon the assumption of parallel axes do not yield accurate results. Hence, for an accurate prediction of bearing performance characteristic it is very essential to include the effect of size of hole and journal misalignment in the analysis. The present work is aimed to analyze the performance characteristics of orifice compensated hole-entry hybrid journal bearing considering the combined influence of hole size and journal misalignment and comparing its performance characteristics with aligned hole-entry hybrid journal bearing without hole size effect for the same bearing geometric and operating parameters. The analysis involves computation of fluid film thickness which varies along circumferential and axial co-ordinates due to journal misalignment and simultaneous solution of Reynolds's equation along with equation of lubricant flow through restrictor as a constraint. The finite element method employing Galerkin's technique has been used to solve Reynolds's equation with proper boundary conditions. Further, the misalignment parameters have been specified in terms of Eulerian angles having first rotation (a) about bearing fixed X-axis and the second rotation (S) about the journal fixed Z'-axis. The journal has been allowed to misalign on a plane iii containing load vectors and on a plane perpendicular to axial plane containing load vector. For the symmetric hole-entry hybrid journal bearing, the static performance characteristics in terms of minimum fluid film thickness, total bearing flow, dynamic performance characteristics in terms of stiffness coefficients, damping coefficients and threshold speed have been studied for hybrid mode of operation of bearing. Those performance characteristics have been studied for selected values of misalignment parameters (a, S) for non- dimensional load (We) and /or restrictor design parameters (cs2). The results indicate that the combined effect of hole size variation and journal misalignment on performance characteristics of both symmetric and asymmetric hole-entry hybrid journal bearing is quite significant when the misalignment and external load is quite large. It is also observed that stability margin of hole- entry hybrid journal bearing configuration reduces as the journal misalignment increase and on the other hand, it increases in asymmetric hole-entry bearing configuration. Iv