Characterization of Foil Bearing Structure for Increasing Shaft Temperatures: Part II—Dynamic Force Performance Conference Paper uri icon

abstract

  • The forced response of a gas foil bearing (GFB), a typical rotor support in oil-free microturbomachinery, relies heavily on its resilient bump-strip layers structure, which also offers dry-friction type damping to ameliorate rotor vibrations. Operation at high temperature not only changes the FB elastic support material properties, but also produces thermal growth of the rotor and bearing components which ultimately affect the bearing structural stiffness and energy dissipation characteristics. The paper presents dynamic shaker load versus foil bearing structural deflection measurements for increasing shaft temperatures, from ambient to 188°C. In the tests, a FB supported on a non-rotating shaft is excited with a shaker at three load amplitudes (13 N, 22 N, and 31 N) and frequencies ranging from 40 to 200 Hz. A mechanical impedance model identifies the frequency dependent FB structural stiffness and equivalent viscous damping coefficient or dry-friction coefficient. Surface plots show trends in test results across increasing dynamic loads, shaft temperatures, and excitation frequencies. The FB stiffness increases by as much as 50% with dynamic loads amplitudes increasing from 13 N to 31 N. The stiffness nearly doubles from low to high frequencies; and most importantly, it decreases by a third as the shaft temperature rises to 188°C. In general, the FB dynamic structural stiffness is lower than its static stiffness, reported in a companion paper, at low excitation frequencies, while it becomes larger with increasing excitation frequency due apparently to a bump slip-stick phenomenon. The bearing viscous damping is inversely proportional to the amplitude of dynamic load, excitation frequency, and shaft temperature. The FB structure dry-friction coefficient decreases with increasing amplitude of applied load and shaft temperature, and increases with increasing excitation frequency. The experimental results demonstrate the paramount effect of operating temperature on the structural parameters of a foil bearing. Copyright © 2008 by ASME.

author list (cited authors)

  • Kim, T. H., San Andrés, L., & Breedlove, A. W.

citation count

  • 7

publication date

  • January 2008

publisher