Rotor Dynamic Characteristics Supported by Multi-Pad Bump Foil Gas Bearings

Bump foil gas bearings (BFGBs) play an important role in high-speed turbomachinery. However, most studies on the dynamic characteristics of BFGBs focus on a one-pad structure composed of a bump foil and a top foil. This paper considers the multi-pad foil structure in BFGBs by developing the finite element model of bump and top foils and introducing nonlinear contact constraints between bearing components. In addition, a transient dynamic model of a rotor and multi-pad bump foil gas bearing (MP-BFGB) system is established through sufficient considerations of coupling effects among rotor, gas film, and foil structures. Nonlinear rotor dynamic responses, including stability and vibration characteristics, are obtained through integrating the transient state variables in the time domain. The results show that the rotor stability can be enhanced by increasing the number of top foil pads, which, however, tends to reduce the bearing load capacity and gas film stiffness. In addition, rotor sub-synchronous vibrations are more prone to appear under greater gas film stiffness.