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Research Papers: Gas Turbines: Structures and Dynamics

Damping and Inertia Coefficients for Two End Sealed Squeeze Film Dampers With a Central Groove: Measurements and Predictions

[+] Author and Article Information
Luis San Andrés

Professor
Mechanical Engineering Department,
Texas A&M University,
College Station, TX 77843
e-mail: Lsanandres@tamu.edu

Sanjeev Seshagiri

Mechanical Engineer,
VYCON, Inc.,
16323 Shoemaker Avenue,
Suite 600,
Cerritos, CA 90703
e-mail: sseshagiri@vyconenergy.com

The designation long and short damper is a convenience for descriptive purposes only.

Lubricant through flow is still needed to evacuate the mechanical energy dissipated, i.e., to keep the oil and solid components cool.

The piston rings are rectangular in cross-section with a slit butt joint; their axial thickness equals 2.35 mm. When installed, the ring outer face pushes against the bearing inner diameter and leaves a gap equal to 0.19 mm with the journal.

The journals do not affect the natural frequency of the bearing and its support structure. Note that the journal and its base affixed to the ground are quite rigid.

The force coefficients reported for the short and long dampers have different normalizing parameters, thus making a direct comparison rather cumbersome. However, the preceding formulas reveal that (CA/CB)~7.4×(C¯A/C¯B), for example.

1Work conducted as a Graduate Research Assistant at Texas A&M University.

Contributed by the Structures and Dynamics Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received June 20, 2013; final manuscript received July 2, 2013; published online September 17, 2013. Editor: David Wisler.

J. Eng. Gas Turbines Power 135(11), 112503 (Sep 17, 2013) (9 pages) Paper No: GTP-13-1173; doi: 10.1115/1.4025033 History: Received June 20, 2013; Revised July 02, 2013

Aircraft engine rotors, invariably supported on rolling element bearings with little damping, are particularly sensitive to rotor imbalance and sudden maneuver loads. Most engines incorporate squeeze film dampers (SFDs) as a means to dissipate mechanical energy from rotor motions and to ensure system stability. The paper experimentally quantifies the dynamic forced performance of two end sealed SFDs with dimensions and an operating envelope akin to those in actual jet engine applications. The current experimental results complement and extend prior research conducted with open ends SFDs (San Andrés, 2012, “Damping and Inertia Coefficients for Two Open Ends Squeeze Film Dampers With a Central Groove: Measurements and Predictions,” ASME J. Eng. Gas Turbines Power, 134, p. 102506). In the tests, two journals make for two SFD configurations, both with a diameter D = 127 mm and nominal radial film clearance c = 0.127 mm. One short length damper has film lands with extent L = 12.7 mm, while the other has 25.4 mm ( = 2L) land lengths. A central groove of length LG = L and depth at ¾ L separates the film lands. A light viscosity lubricant is supplied into the central groove via three orifices, 120 deg apart, and then flows through the film lands whose ends are sealed with tight piston rings. The oil pushes through the piston rings to discharge at ambient pressure. In the tests, a static load device pulls the damper structure to increasing eccentricities (maximum 0.38c) and external shakers exert single-frequency loads 50–250 Hz, inducing circular orbits with amplitudes equaling ∼5% of the film clearance. The lubricant feed and groove pressures and flow rates through the top and bottom film lands are recorded to determine the flow resistances through the film lands and the end seals. Measured dynamic pressures in the central groove are as large as those in the film lands, thus demonstrating a strong flow interaction, further intensified by the piston ring end seals which are effective in preventing side leakage. Dynamic pressures and reaction loads are substantially higher than those recorded with the open ends dampers. Comparisons to test results for two identical damper configurations but open ended (San Andrés, 2012, “Damping and Inertia Coefficients for Two Open Ends Squeeze Film Dampers With a Central Groove: Measurements and Predictions,” ASME J. Eng. Gas Turbines Power, 134, p. 102506) demonstrate at least a threefold increase in direct damping coefficients and no less than a double increment in added mass coefficients. Predictions from a physics-based model that includes the central groove, the lubricant feed holes, and the end seals' flow conductances are in agreement with the test results for the short length damper. For the long damper, the predicted damping coefficients are in good agreement with the measurements, while the added masses are under-predicted by ∼25%.

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References

Figures

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Fig. 1

Cross section view of the SFD test rig and lubricant flow path through damper film lands (long journal with piston rings installed). Insets: (a) the BC axes and the static loader placement, and (b) the faces of the piston ring installed in the BC; face A is towards ambient.

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Fig. 2

Sealed ends short SFD: test damping (C¯XX,C¯YY)SFD and added mass (M¯XX,M¯YY)SFD coefficients versus the static eccentricity (eS/cB). Circular orbits of amplitude r = 0.055cB.

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Fig. 3

Sealed ends long SFD: test damping (C¯XX,C¯YY)SFD and added mass (M¯XX,M¯YY)SFD coefficients versus the static eccentricity (eS/cA). Circular orbits of amplitude r = 0.054cA.

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Fig. 4

Disposition of dynamic pressure sensors in the long damper configuration (LA = 25.4 mm)

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Fig. 5

Sealed ends short length SFD: peak-peak dynamic pressures in the film lands and in the central groove versus the whirl frequency. Centered bearing eS = 0; circular orbit r = 0.1cB. Static pressure in the groove: PG = 0.72 bar.

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Fig. 6

Sealed ends long SFD: peak-peak dynamic pressures in the film lands and in the central groove versus the whirl frequency. Centered bearing eS = 0; circular orbit r = 0.1cA. Static pressure in the groove: PG = 4.69 bar.

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Fig. 7

Short length open and sealed ends SFDs: comparison of the damping and inertia coefficients versus the static eccentricity. The data for the open ends SFD are from Ref. [26].

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Fig. 8

Open and sealed ends long SFDs: comparison of the damping and inertia coefficients versus the static eccentricity. The data for the open ends SFD are from Ref. [26].

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Fig. 9

Sealed ends short length SFD: the predicted and experimental damping (C¯XX,C¯YY)SFD and added mass (M¯XX,M¯YY)SFD coefficients versus the static eccentricity

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Fig. 10

Sealed ends long SFD: the predicted and experimental damping (C¯XX,C¯YY)SFD and added mass (M¯XX,M¯YY)SFD coefficients versus the static eccentricity

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Fig. 11

Hydraulic circuit diagram for the SFD with end seals

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