Experimental and Analytical Investigation of Squeeze Film Bearing Damper Forces Induced by Offset Circular Whirl Orbits

Abstract

A basic research program was conducted to investigate the hydrodynamic forces of a squeeze film bearing damper. These forces were induced by controlled offset circular whirl orbits of the damper journal. The orbits were mechanically produced by eccentric damper rings and cams in a specially designed, end sealed test rig. Aircraft engine damper geometry and operating conditions were simulated. The instantaneous circumferential pressure profiles, for specific orbits, were measured by eight high response pressure transducers. From these data, twelve composite pressure plots were developed; each was numerically integrated to determine the damper forces corresponding to every 30 deg position of the damper center, i.e., 0–360 deg. The variations in oil film thickness data were monitored via two proximity probes. A numerical method which uses the proximity test data and the damper geometry to calculate the instantaneous values of damper center eccentricity (e), phase angle (φ), radial velocity (e˙), and whirl velocity (φ˙) is presented. These test values are required to compare theory with test. Since the data reduction for offset orbits is extremely complicated, this simple method was found to be very useful in analyzing the test results. Test results for pressure profiles as well as damper forces were compared with theoretical predictions. Agreement was good. The analysis is based on “long bearing” solution of Reynolds equation and includes the effect of inlet and cavitation pressures. For the cavitated oil film, inlet pressure was shown to have important effect on damper forces.