A linear fluid inertia model for improved prediction of force coefficients in grooved squeeze film dampers and grooved oil seal rings.

摘要

In Squeeze Film Dampers, (SFD), grooves (deep or shallow) are used to feed oil into the damper and prevent oil starvation within the fluid film lands. In oil seals with film land of clearance c, short shallow grooves (depth &le 15c, length &le 30c) are machined to reduce the cross-coupled stiffness coefficients, and thus improve the seal stability characteristics. Moreover, test stands for these devices can also incorporate grooves or recesses as part of oil feeding/discharge arrangements. A common assumption is that these grooves do not influence the test system forced response. However, unexpected large added mass coefficients are reported in these configurations and not adequately predicted. In the case of grooved oil seals, experimental results also show that circumferential grooves do aid to reduce cross-coupled force coefficients but to a lesser extent than predictions otherwise indicate.A linear fluid inertia model for analysis of multiple-groove SFD or oil seal configurations is advanced. A perturbation analysis for small motion about a journal centered and off-centered position yields zeroth and first order flow equations defined at each individual flow region (land and grooves) of constant clearance (c). The analysis considers both the circumferential and axial dynamic pressure variations across the groove and land regions. At the groove regions, an effective groove depth (d eta) and effective clearance (ceta = deta + C) are defined based on qualitative observations of the laminar flow pattern through annular cavities. This depth differs from the actual physical groove depth. The boundary conditions at the inlet and exit plane are a function of the geometric configuration. Integration of the resulting dynamic pressure fields on the journal surface yields the force coefficients (stiffness, damping, and inertia).Comparisons between predicted and experimental force coefficients for a grooved oil seal and a SFD show excellent correlation over a narrow range of effective groove depths. The results confirm that large added mass coefficients are associated to the feed/discharge grooves in the scrutinized test configurations. Furthermore, predictions, benchmarking experimental data, corroborate that short inner land grooves in an oil seal do not isolate the pressure field of the adjacent film lands, and hence contribute greatly to the force response of the seal.