Parametric Studies on Dynamic Performance of Hydrostatic Flexure Pivot Tilting Pad Gas Bearing With Radial Compliance

Abstract

Flexure pivot tilting pad gas bearings are recognized as an alternative to foil gas bearing [1, 2] for high speed turbomachinery, due to their capability to provide high rotor-bearing stability and simple structure. The flexure pivot design eliminates wear problem of axial pins or sockets at the pivots which are common in traditional tilting pad bearings. Added features such as a pivot offset and pad preloads can also be optimized to further improve the stability. Hybrid flexure pivot tilting pad gas bearing have also been reported [3]. The hybrid bearing has a direct air supply to the bearing clearance through a tiny orifice. It has shown that the hybrid operation of the tilting pad gas bearing can also increase the rotor-bearing stability [3]. In many microturbomachinery applications, hollow shafts are adopted to reduce the rotor weight and increase the bending critical speeds. However, the hollow shaft has a large centrifugal growth at high speeds requiring the gas bearing to have radial compliances. However, the radial compliance within the tilting pads can compromise the rotor-bearing stability because large displacement of the pads along the radial direction can cause hydrodynamic rotor-bearing instability associated with the increased bearing clearance (i.e. decreased effective preload) if the radial stiffness is not designed properly. Analytical studies show that optimal choice of pad radial stiffness could extend operating envelope of flexure pivot tilting pad gas bearing without deteriorating rotor-bearing stability [4]. High speed operation can generate significant amount of heat and adequate heat dissipation mechanism should also be developed. Hybrid operation is considered to have added benefit of effective cooling capability. This paper presents design studies on hybrid flexure tilting pad gas bearing with radial compliance which can accommodate large rotor centrifugal growth and also provide effective cooling mechanism.