TO STUDY THE PERFORMANCE CHARACTERISTICS OF TOTAL CROSS FLOW (TCF) MULTIRECESS HYDROSTATIC/HYBRID JOURNAL BEARING

Abstract

Externally pressurized journal bearing have been known as early as 1865. Currently, they are commonly used in various technology because of the advantage of complete freedom from wear and excellent characteristics with respect to fluid film stiffness, low friction, good vibration damping characteristics and smooth relative motion even at low rotational speeds. A conventional hydrostatic bearing unlike a. hydrodynamic bearing has its sliding surfaces continuously and completely separated by a pressurized oil film under static and dynamic conditions within the design range. The main problem with conventional design of hydrostatic bearing has been the undesirable hydrodynamic effect associated with the oil turbulence in the pocket under critical dynamic condition. This is because of the friction losses due to shearing of oil both in pressurized pocket and under the lands can become excessive. Total Cross Flow (TCF) hydrostatic bearing is an externally pressurized bearing with design feature to overcome most of the side effect of conventional journal Bearing (CJB) i.e. drag resistance, cavitation and whirl etc. With the properties of good damping, stiffness and low temperature rise the TCF hydrostatic bearings are considered suitable for high speed application. In recent years, considerable amount of research has been carried out and reported in the area of multirecess compensated hydrostatic/hybrid journal bearing system. To the best knowledge of candidate no comprehensive study is yet available in literature which addresses the influence of the grooved lands on the performance of TCF hydrostatic/hybrid journal bearing system with capillary as a compensating element. Thus, the work presented in the report is aimed to study the influence of groove pitch (2g) and groove angle (Bg) on the performance of bearing. The following paragraphs briefly detail the work presented in this report. 111 The analysis of a TCF multirecess compensated hydrostatic/hybrid journal bearing system requires the solution of Reynolds equation governing the flow of lubricant in the bearing clearance space together with the equation of flow of lubricant through the restrictor as a constraint along with appropriate boundary conditions. The finite element method has been used to obtain the solution of relevant governing equations. The system equation for the lubricant flow field has been derived using the orthogonality condition of Galerkin's technique. The shape of the groove undertaken in this study is trapezoidal in which pitch varies in the range of 1 mm-2mm and the groove angles are 600, 100°, 1500. The shape of the recess consider is rectangular with capillary as a compensating element. The bearing performance characteristics of 4-pocket TCF hydrostatic/hybrid journal bearing have been obtained in terms of maximum fluid film pressure (ax)' bearing flow (Q), fluid film stiffness coefficients (1'22)' fluid film damping coefficients (I'2) ,critical journal mass (M~ )and the stability threshold speed margin(if) for the generally used bearing operating and geometric parameters as shown in Table 4.1 and 4.2. Results computed from the study indicates that from the point of view of, the fluid film stiffness, the TCF rigid bearing at groove pitch (Ag) =1 mm and groove angle (9g) =150° is likely to provide better performance in comparison to conventional hydrostatic journal bearings and hence a designer can select an appropriate bearing geometry from the following criterion: 'SI11221TCF(Ag=lmm,Og=150°) > SII/ 22ICJB lI/22TCF(Ag=Imm,Og100°) 511/22ITCF(tg=Imm,Og=60°) The results presented in this report are expected to be quite useful to the bearing designers.