Numerical and experimental studies on stability of cryogenic turbo-expander with protuberant foil gas bearings

High speed turbo-expander is an essential refrigerating component in cryogenic systems. In addition to thermodynamic performance, its stability in transient high speed operation is also of great concern for its comprehensive performance. Oil free foil bearing has a great application potential in high speed turbomachinery by virtue of its high stability with no extra external supplying gas. In this paper, finite element model of a 150 Nm³/h cryogenic turbo-expander using foil bearing for air separation is configured for a case study. Influence of bearing structural stiffness and damping characteristics on the rotor-foil bearing system are evaluated for stable operation. Static structural stiffness and damping coefficients of the protuberant foil journal bearing and thrust bearings are obtained from the static loading and deflection tests. With the tested coefficients, rotordynamic performances of the rotor-bearing system is analyzed numerically and compared with the transient experimental results.