An Experimental Study of High-Speed Rotors Supported by Air-Lubricated Foil Bearings—Part 1: Rotation in Pressurized and Self-Acting Foil Bearings

Abstract

A high-speed rotor, supported by an air-lubricated foil bearing, is rotated in both the vertical and horizontal attitudes at speeds in excess of 60,000 rpm. The rotor is stable and free from “half-frequency” or “fractional-frequency” whirl instability encountered in conventional gas bearings. External pressurization is applied to separate the foil surfaces from the journal during the initial and final stages of rotation, with adequate self-acting support and foil separation established at relatively low transition speeds. In the pressurized mode of operation, the system is characterized by a series of ultra-harmonic resonances, of sharply defined frequencies, related by fractions to speeds of synchronous resonance. In the self-acting mode of operation, the response of the system to residual imbalance is influenced by both the foil bearing and by the pressurized thrust bearings. The magnitude of the air gap (clearance) is determined at various rotational speeds and compared with theoretically predicted results. The temperature rise of the foil with speed is measured at various locations in order to assess its contribution to clearance growth. The journal and foil surfaces are examined and it is found that the foil bearing is endowed with excellent wipe-wear characteristics.

Discussion: “The Dynamic Characteristics of a Turborotor Simulator Supported on Gas-Lubricated Foil Bearings—Part 2: Operation With Heating and Thermal Gradients” (Licht, L., 1970, ASME J. Lubr. Technol., 92, pp. 650–659)

“…Few will take issue with Mr. Cherubim's observation that foils contract on cooling and his deduction that this may affect the magnitude of the gap width. The influence of dissipative heating and convective cooling was discussed in considerable detail in references [3] and [4], Part 2. In particular, the transient gap width during coastdown, following a sudden decrease in the rate of convective cooling, is shown in Fig.…”

“…In particular, the transient gap width during coastdown, following a sudden decrease in the rate of convective cooling, is shown in Fig. 13 of reference [3].…”