Dynamic Forced Performance of Short Length Open-Ends Squeeze Film Damper with End Grooves

Abstract

Squeeze Film Dampers (SFDs) are effective means to reduce shaft vibration and eliminate instabilities in high performance rotating machinery. Presently there is a need to characterize the performance of ultra-short length SFDs for aero jet engines where overall weight and space are at a premium. The paper presents force coefficients and dynamic film pressures measured in an open ends SFD with slenderness ratio L/D = 0.2 and for two film clearances c _A  = 0.129 mm and c _B  = 0.254 mm. The film land length L = 25.4 mm and diameter D = 125.7 mm. ISO VG2 lubricant flows into the axial mid-plane of the film land through three orifices spaced 120^o. The journal has end grooves (width and depth = 2.5 × 3.8 mm) for the installation of piston rings, and hence the total wetted length L _tot  = 36.8 mm. A static loader pulls the bearing cartridge (BC) to a set static eccentricity (e _s ), and two shakers, orthogonally positioned, exert dynamic loads on the BC to create circular orbits of amplitude (r) over a range of whirl frequencies (ω). In the current tests, the end seals are not in place. Comparing the dynamic forced performance of the open ends SFDs, the small clearance damper generates about four times more damping than the one with a larger clearance, whereas the inertia coefficients are approximately twice as large. The test results modestly agree with the theoretical ratios, where damping scales with ~1/c ³ and inertia with ~1/c. The measurements also evidence significant dynamic pressures at the end grooves, which amplify the test elements’ inertia coefficients. The test results continue to demonstrate the paramount effect of grooves on enhancing the dynamic forced response of SFDs.

Gary Bradley: Work conducted as a research assistant while at Texas A&M University.