Dynamic Performance of an O-Ring Sealed Squeeze Film Damper and a Simple Way to Estimate the (Ingested) Gas Content in a Squeeze Film

Completing a long-term project characterizing squeeze film dampers (SFDs) for air breathing engines, the paper presents complete measurements of the forced performance of an elastic structure hosting an OR-sealed damper (OR-SFD) and the identification of physical parameters, namely stiffness and damping, for the dry structure, the ORs, and the lubricated OR-SFD. The damper with slenderness ratio L/D = 0.2 and radial clearance c ~ 0.002 D is lubricated a light oil supplied at 0.69 bar(g). Shakers produce circular whirl motions of the test system with amplitude r = 0.05c to 0.45c and frequency \(\omega\)  = 10 Hz to 70 Hz (max. Squeeze velocity vs = r \(\omega\) =55 mm/s). The ORs force coefficients are a function of the orbit amplitude and nearly invariant with frequency. The ORs centering stiffness quickly decreases with amplitude, likely due to the extensive deformation and slow elastic recovery in the ORs’ material bonds. As the whirl amplitude grows, the ORs viscous damping (COR) reduces from 10% to 3% of the lubricated system damping. For small orbit radii, r ≤ 0.25 c, the SFD added mass (MSFD) and viscous damping (CSFD) coefficients approach predictions for a fully sealed damper. For moderate size orbits (r = 0.45 c), MSFD drops by 75% and COR decreases by ~ 40% due to persistent air ingestion for motions with vs > 24.5 mm/s. Videos show a bubbly mixture in the return line and also through the damper top end exposed to ambient. Over a certain elapsed time, a simple procedure draws into a deflated balloon the material contents in the film. The novel approach estimates the gas volume fraction (GVF) that rapidly increases as vs grows. The findings quantify the deterioration of ORs force coefficients, their inability to keep the lubricant sealed, and their limited ability to prevent persistent air ingestion into the film land.