COMBINED INFLUENCE OF JOURNAL MISALIGNMENT AND. RECESS SHAPE ON THE PERFORMANCE OF HYDROSTATIC- JOURNAL BEARING SYSTEM

Abstract

The multirecess hydrostatic/ hybrid journal bearings have found 'extensive use in engineering applications such as machine tools, test equipments, radio telescope and in the aerospace industry. Their wide acceptability in the engineering applications is mainly owing to their excellent characteristics in respect of high fluid film thickness, high load carrying capacity at zero loads and zero speed, long life and smooth operation, good rotational accuracy and large fluid film damping coefficient. The journal misalignment in hydrostatic/ hybrid journal bearing may be caused, generally, by non-central loading, moment produced by couple forces on the journal, shaft deflections due to elastic and thermal distortion and assembly errors. Thus the bearing performance characteristics gets affected due to the journal misalignment Therefore, the analysis based upon the, assumption of parallel axes do not yield accurate results. Therefore, an accurate prediction of bearing performance characteristics it is essential to include journal misalignment in the analysis. It has also been observed from the literature that in most of the studies, the geometric shape of recesses used in hydrostatic/ hybrid journal bearing system is mainly rectangular. This could be due to ease in manufacturing and relative simplicity of this particular geometric shape of the recess. However, with the advent of newer and sophisticated manufacturing techniques such as CAM, EDM etc., the other geometric recess shapes (circular, elliptical and triangular) can also be easily manufactured. It has also been observed that the combined influence of misalignment and variation geometric in shape of recess for capillary compensated hydrostatic/ hybrid journal bearing system, have not been studied yet. The present work is therefore, aimed to analyze the performance of a capillary compensated hydrostatic/ hybrid journal bearing system by considering the combined influence of recess shape and journal misalignment into account and comparing its performance characteristics with aligned square recessed shape hydrostatic/ hybrid journal bearing. The analysis involves the simultaneous solution of Reynold'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 Reynold'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 misaligned on an axial plane containing load vector and on a plane perpendicular to the axial plane containing load vector. The study indicates that the performance of a capillary compensated hydrostatic/ hybrid journal bearing system gets affected significantly due to geometric shape of recess and journal misalignment. In order to have an optimum performance of a capillary compensated misaligned journal bearing a proper selection of geometric shape of recess, misalignment parameter (ff ands) , speed parameter(Q) , external load (W0) , restrictor design parameter (CS2) is essential.