Mechanical Engineering Faculty Research

Title

A Three-Dimensional Parametric Study and Numerical/Experimental Flow Visualization of a Six-Pocket Hydrostatic Journal Bearing

Document Type

Article

Publication Date

Winter 1-2012

Abstract

This article presents a numerical investigation and some experimental results supporting evidence on the flow structure and the pressure distribution in a hydrostatic journal bearing with six equidistant pockets. The parametric studies are of both operational and geometric nature. The operational ones include shaft's angular speed and inlet pressure. The geometric ones include pocket depth, eccentricity, clearance and restrictor diameter. The latter two are instrumental in changing the ratio of the restrictor to clearance hydraulic resistance (R). The flow regime in the bearing is kept in the laminar range (Rebrg < 60). It was found that for the deep pocket the pressure is uniformly distributed across its circumferential length, whereas for the shallow pocket it increases in a ramp fashion along the direction of rotation. The oil injected through the restrictor forms a penetrating jet that constitutes the driver of the upstream and downstream vortical cells that eventually interact with the Couette effect generated by the rotating shaft. This latter effect deforms both the upstream and downstream vortical cells, causing the downstream one to elongate and occupy a large portion of the pocket center. A direct consequence is the formation of a central vortical cell located at the mouth of the restrictor. It has become evident that the flow in the restrictor has to be modeled when simulating the flow in the pockets, because it represents an influential boundary condition that significantly alters the structure of the flow in the pocket itself. A novel modeling feature is the introduction of large sink-type reservoirs upstream of the restrictors. This allows prescription of the same pressure at the inlet of these ‘sinks’, thus simulating a common and constant pressure manifold for all restrictors. For high speeds of rotation the pressure on the lands between the pockets is dominated by hydrodynamic effects, which cause pressures higher than the hydrostatic pressure in the convergent zone. This situation has important consequences on the overall flow structure in pockets adjacent to these large hydrodynamic pressures, as the flow may be completely shut off at the circumferential and partially at the axial exits of the pocket. The change in the resistance R is associated with the change in the hydrodynamic to hydrostatic pressure component dominance in the bearing. Some validating qualitative experimental results concerning the numerical simulation of the flow in the pockets and associated feed mass flows are also presented.

Publication Title

Tribology Transactions

Volume

56

Issue

1

First Page

1

Last Page

26