Rotordynamic Performance of Flexure Pivot Hydrostatic Gas Bearings for Oil-Free Turbomachinery

Abstract

Micro-turbomachinery demands gas bearings to ensure compactness, lightweight and extreme temperature operation. Gas bearings with large stiffness and damping, and preferably of low cost, will enable successful commercial applications. Presently, tests conducted on a small rotor supported on flexure pivot–hydrostatic pad gas bearings (FPTPBs) demonstrate stable rotordynamic responses up to 100,000 rpm (limit of the drive motor). Test rotor responses show the feed pressure raises the system critical speed (increase in bearing direct stiffness) while the viscous damping ratio decreases. Predictions correlate favorably with experimentally identified (synchronous) direct stiffness bearing force coefficients. Identified experimental gas bearing synchronous damping coefficients are 50% or less of the predicted magnitudes, though remaining relatively constant as the rotor speed increases. Tests without feed pressure show the rotor becomes unstable at ∼ 81 krpm with a whirl frequency ratio of 20%. FPTPBs are mechanically complex and more expensive than cylindrical plain bearings. However, their enhanced stability characteristics and predictable rotordynamic performance makes them desirable for the envisioned oil-free applications in high speed micro turbomachinery.

Motion analysis of a rotor supported by self-acting axial groove gas bearing system with double time delays

“…[1][2][3][4][5] The performances of the hydrostatic gas journal bearings and the flexure pivot hydrostatic gas tilting-pad bearings were investigated theoretically and experimentally by Liu et al 6 and Zhu and Andres. 7 Their works provided better support in the application of the hydrostatic gas bearings for oil-free turbomachinery. Yang et al 8,9 analyzed the dynamic coefficients and stability of the aerodynamic tiltingpad journal bearings using the linear theory.…”