The transition from hydrodynamic to boundary regime of tilting thrust pads

Abstract

The fundamental problem of the hydrodynamic lubrication of thrust pads is now well understood, especially in the simple case of flat tilting pads resting on a flat race. Sophisticated theories¹ have been developed to extend the solution for a rectangular pad of infinite width to the case of finite, sector shaped pads. The problem of transition from the hydrodynamic regime to the boundary regime is more intricate, however, and has been given less attention than the simple problem for radial bearings. Furthermore, in any theoretical work, the pivoting axis is implicitly assumed to be located within the active friction face; the circumferential offset of this axis is the only variable taken into account². The analysis of the state of equilibrium of all the forces applied to the pad in both lubrication regimes has suggested that the axial offset of the radial pivot has an influence. A special tribometer has been designed and used to investigate the laws governing the transition phenomena³. The influence of the pivot location on the fluid hydrodynamic friction has been considered but the most significant results have been obtained by investigating the influence of the tilting conditions on the transition critical point. The accurate definition and detection of this threshold is based upon a specially developed electrical method. These results are summarized in terms of the equivalent rectangular pad and lead to interesting conclusions allowing an optimum layout of the pad and its support to be derived.