Measurements of Pressure Distributions and Force Coefficients in a Squeeze Film Damper Part I: Fully Open Ended Configuration

Jung, Si Young; Andrés, Luis San; Vance, John M.

doi:10.1080/10402009108982047

Cited by 20 publications

(8 citation statements)

References 5 publications

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“…As early as in 1991, a photograph in Ref. [15] shows a jet-like outflow through the PR slit. Thus, the outflow through a PR slit with area A slit is modeled as…”

Section: Fundaments Of Sfd Analysis and Identification Of Force Coeffmentioning

confidence: 99%

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Experimental Force Coefficients for Two Sealed Ends Squeeze Film Dampers (Piston Rings and O-Rings): An Assessment of Their Similarities and Differences

Andrés

Koo

Jeung

2018

Volume 7B: Structures and Dynamics

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Squeeze film dampers (SFDs) in aircraft engines effectively aid to reduce rotor motion amplitudes, in particular when traversing a critical speed, and help to alleviate rotor whirl instabilities. The current work is a long term endeavor focused on quantifying the dynamic force performance of practical SFDs, exploring novel design damper configurations, and producing physically sound predictive SFD models validated by experimental data. Piston rings (PRs) and O-rings (ORs), commonly used as end seals in SFDs for commercial and military gas turbine engines, respectively, amplify viscous damping in a short physical length and while operating with a modicum of lubricant flow. This paper presents experimental force coefficients (damping and inertia) for two identical geometry SFDs with end seals, one configuration hosts PRs, and the other one ORs. The test rig comprises a stationary journal and bearing cartridge (BC) hosting the SFD and supported on four elastic rods to emulate a squirrel cage. The damper film land length, diameter and clearance are L = 25.4 mm, D = 5L, and c = 0.373 mm (D/c = 340), respectively. A supply feeds ISO VG 2 oil to the film land at its middle plane through either one hole or three holes, 2.5 mm in diameter, 120° apart. In the PR-SFD, the lubricant exits thru the slit opening at the ring butted ends. The O-rings suppress oil leakage; hence, lubricant evacuates through a 1 mm hole at ¼ L near one journal end. The O-rings when installed add significant stiffness and damping to the test structure. The ORSFD produces 20% more damping than the PR-SFD, whereas both sealed ends SFDs show similar size added mass. For oil supplied at 0.69 bar(g) through a single orifice produces larger damping, 60% to 80% more than when the damper operates with three oil feedholes. A computational model reproducing the test conditions delivers force coefficients in agreement with the test data. Archival literature calls for measurement of a single pressure signal to estimate SFD reaction forces. For circular centered orbits, the dynamic pressure field, in the absence of any geometrical asymmetry or feed/discharge oil condition, “rotates” around the bearing with a speed equal to the whirl frequency. The paper presents force coefficients estimated from (a) measurements of the applied forces and ensuing displacements, and (b) the dynamic pressure recorded at a fixed angular location and “integrated” over the journal surface. The first method delivers a damping coefficient that is large even with lubricant supplied at a low oil supply pressure whereas the inertia coefficient increases steadily with feed pressure. Predictions show good agreement with the test results, in particular the added mass. On the other hand, identified damping and inertia coefficients from dynamic pressures show a marked difference from one pressure sensor to another, and vastly disagreeing with test results from the first method or predictions. The rationale for the discrepancy relies on local distortions in the dynamic pressure fields that show zones of oil vapor cavitation at a near zero absolute pressure and/or with air ingestion producing high frequency spikes from bubble collapsing; both phenomena depend on the magnitude of the oil supply pressure. An increase in lubricant supply pressure suppresses both oil vapor cavitation and air ingestion which produces an increase of both damping and inertia force coefficients. No prior art compares the performance of a PR-SFD vis-à-vis that of an OR-SFD. Supplying lubricant with a large enough pressure (flow rate) is crucial to avoid the pervasiveness of air ingestion. Lastly, the discussion on force coefficients obtained from two distinct methods questions the use of an oversimplifying assumption; the dynamic pressure field is not invariant in a rotating coordinate frame.

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“…As early as in 1991, a photograph in Ref. [15] shows a jet-like outflow through the PR slit. Thus, the outflow through a PR slit with area A slit is modeled as…”

Section: Fundaments Of Sfd Analysis and Identification Of Force Coeffmentioning

confidence: 99%

“…Zeidan and Vance [13] note that PR-SFDs are prone to both vapor and gaseous oil cavitation that eventually reduce the damper load capacity. As a result, Meng et al [14] and Jung et al [15,16] introduced a novel serrated piston ring that lessens the distorting pressure effect because of the jet-like outflow through the PR slit.…”

Section: Introductionmentioning

confidence: 99%

Experimental Force Coefficients for Two Sealed Ends Squeeze Film Dampers (Piston Rings and O-Rings): An Assessment of Their Similarities and Differences

Andrés

Koo

Jeung

2018

Volume 7B: Structures and Dynamics

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“…Radial motions from either a centred or an eccentric position were "rst investigated. Similar to tests of circular-centred journal motions in squeeze-"lm dampers [e.g., San Andres & Vance (1987c) or Jung et al (1991)], simple radial motions are very useful for the current experimental squeeze-"lm studies, since only some, in this case three of the seven, force terms are involved. Following the radial motion studies, quasi-straight-line motion with initial eccentricity perpendicular to the motion direction (called o!set-linear motion) was used to evaluate the remaining force terms.…”

Section: Introductionmentioning

confidence: 97%

Nonlinear Fluid Forces in Cylindrical Squeeze Films. Part Ii: Finite Length

Han

Rogers

2001

Journal of Fluids and Structures

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“…[35][36][37][38][39][40] Della Pietra and Adiletta, and Tichy investigated the influence of different PRs on SFDs. Several studies investigated the effect of various sealing types like gap seals, O-rings or other types of mechanical sealing devices.…”

Section: Introductionmentioning

confidence: 99%

Wear Behavior of Laser‐Patterned Piston Rings in Squeeze Film Dampers

Rosenkranz

Jaeger²,

Gachot

et al. 2015

Adv Eng Mater

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Machine components experience large tribological stresses during their lifetime. Due to the kinematics and the applied load, many of these components work under mixed or boundary lubrication conditions, with direct contact of both rubbing surfaces. Wear, thus plays a significant role in these two lubrication regimes, determining component life time. Laser surface patterning (LSP) can produce a well-defined surface topography in order to improve the tribological properties under boundary and mixed lubrication, including reduced wear. In this research work, the piston rings (PRs) of a squeeze film damper (SFD, stainless steel MSRR 6503) are patterned with a dot-like surface structure (4 mm spacing and ca. 1 mm depth) produced by three-beam laser interference from a solid state Nd:YAG laser with a pulse duration of 10 ns and wavelength of 355 nm. The wear behavior of these laser-patterned PRs is compared to that of conventional ground PRs. The tribological tests are performed on a special test rig for SFDs. The tested surfaces are then analyzed by white light interferometry in order to study the underlying wear mechanism and to estimate the corresponding wear volume. This analysis demonstrates an 85% reduction in the wear volume of the laser-patterned PRs. The designed surface topography can store wear particles in the topographic minima, removing them from the contact zone, thus reducing the amount of abrasive wear and the wear volume.

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Measurements of Pressure Distributions and Force Coefficients in a Squeeze Film Damper Part I: Fully Open Ended Configuration

Cited by 20 publications

References 5 publications

Experimental Force Coefficients for Two Sealed Ends Squeeze Film Dampers (Piston Rings and O-Rings): An Assessment of Their Similarities and Differences

Experimental Force Coefficients for Two Sealed Ends Squeeze Film Dampers (Piston Rings and O-Rings): An Assessment of Their Similarities and Differences

Nonlinear Fluid Forces in Cylindrical Squeeze Films. Part Ii: Finite Length

Wear Behavior of Laser‐Patterned Piston Rings in Squeeze Film Dampers

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