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 intothe damper and prevent oil starvation within the fluid film lands. In oil seals with filmland of clearance c, short shallow grooves (depth ? 15c, length ? 30c) are machined toreduce the cross-coupled stiffness coefficients, and thus improve the seal stabilitycharacteristics. Moreover, test stands for these devices can also incorporate grooves orrecesses as part of oil feeding/ discharge arrangements. A common assumption is thatthese grooves do not influence the test system forced response. However, unexpectedlarge added mass coefficients are reported in these configurations and not adequatelypredicted. In the case of grooved oil seals, experimental results also show thatcircumferential grooves do aid to reduce cross-coupled force coefficients but to a lesserextent than predictions otherwise indicate.A linear fluid inertia model for analysis of multiple-groove SFD or oil sealconfigurations is advanced. A perturbation analysis for small motion about a journalcentered and off-centered position yields zeroth and first order flow equations defined ateach individual flow region (land and grooves) of constant clearance ( c ).The analysisconsiders both the circumferential and axial dynamic pressure variations across thegroove and land regions. At the groove regions, an effective groove depth ( d? ) andeffective clearance (c d c ? ? = + ) are defined based on qualitative observations of thelaminar flow pattern through annular cavities. This depth differs from the actual physicalgroove 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 thejournal surface yields the force coefficients (stiffness, damping, and inertia).Comparisons between predicted and experimental force coefficients for a groovedoil seal and a SFD show excellent correlation over a narrow range of effective groovedepths. The results confirm that large added mass coefficients are associated to thefeed/discharge grooves in the scrutinized test configurations. Furthermore, predictions,benchmarking experimental data, corroborate that short inner land grooves in an oil sealdo not isolate the pressure field of the adjacent film lands, and hence contribute greatlyto the force response of the seal.