Experimental Observation of Cavitating Squeeze-Film Dampers

Abstract

This paper presents the results of an experimental investigation intended to observe cavitation in squeeze-film bearing dampers representative of those commonly found in aircraft gas turbine engines. Two different squeeze-film damper geometries were tested with both high-speed motion pictures and stroboscopic video recordings acquired at speeds up to 20,000 r/min. The results presented are limited to 8000 r/min due to the increased clarity of the photos acquired at the lower speeds and the similarity of trends at the higher speeds. Comparisons are also made with analysis formulated to handle the dynamics of the film rupture for the “short” damper case. The test results confirmed several of the commonly held “short” bearing assumptions (i.e., predominant axial flow and the effect of supply pressure and eccentricity on the cavitation zone). However, the test results demonstrated that significant flow reversals and film rupture were experienced in the feed/drain grooves in contradiction to the assumed boundary conditions. While agreement between analysis and test is of the right order of magnitude in predicting the cavitation zone shape and circumferential extent, current analyses do not adequately account for the observed variations in the boundaries and change in shape of the cavitation zone.