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Research Papers: Gas Turbines: Structures and Dynamics

Transient Response of a Short-Length (L/D = 0.2) Open-Ends Elastically Supported Squeeze Film Damper: Centered and Largely Off-Centered Whirl Motions

[+] Author and Article Information
Luis San Andrés

Mast–Childs Chair Professor
Fellow ASME
Turbomachinery Laboratory,
Mechanical Engineering Department,
Texas A&M University,
College Station, TX 77843
e-mail: Lsanandres@tamu.edu

Sean Den

Mechanical Maintenance Engineer
Formosa Plastics Corp.,
Point Comfort, TX 77978
e-mail: Sean.thewind@yahoo.com

Sung-Hwa Jeung

Graduate Research Assistant
Turbomachinery Laboratory,
Mechanical Engineering Department,
Texas A&M University,
College Station, TX 77843
e-mail: Sean.jeung@gmail.com

1Work conducted as a graduate research assistant at Texas A&M University.

2Corresponding author.

Contributed by the Structures and Dynamics Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received June 11, 2016; final manuscript received June 19, 2016; published online August 2, 2016. Editor: David Wisler.

J. Eng. Gas Turbines Power 138(12), 122503 (Aug 02, 2016) (11 pages) Paper No: GTP-16-1210; doi: 10.1115/1.4034002 History: Received June 11, 2016; Revised June 19, 2016

Commonly employed in air breathing (gas turbine) engines, squeeze film dampers (SFDs) reduce the amplitude of rotor vibration while traversing system critical speeds or in transient events such as during a maneuver load, a hard landing, a blade loss, or an engine startup/shutdown sequence that could instantaneously shift a damper journal eccentricity (es) to near its clearance (c). Experiments investigate the dynamic force performance of an open ends, short-length (L/D = 0.2) SFD test rig with radial clearance c = 267 μm and undergoing centered (es/c = 0) to largely off-centered (es/c → 1) whirl orbit motions induced by both a large static load plus a dynamic load. Four rods, symmetrically arranged to resemble a squirrel cage, elastically support the SFD test rig. A hydraulic load system displaces the test damper structure into static eccentricity (es/c). One of two types of dynamic load with amplitude FX = FY excite the SFD: a single-frequency, stepping from low frequency to high frequency discretely; or a sine-sweep frequency growing linearly with time at 6 Hz/s, 33 Hz/s, 40 Hz/s, or 55 Hz/s. For motions departing from es/c = 0.0, 0.95, and 0.99, the dynamic load uses a sine-sweep frequency varying from 5 Hz to 245 Hz and evolving rapidly at ∼33 Hz/s. Measurements of SFD displacements characterize the behavior of the SFD rig during its transient response which crosses two system natural frequencies. For motions departing from a largely off-centered condition (es → c), the dynamic load forces the damper to whirl with highly elliptical orbits, in particular while crossing a resonance (damped natural frequency). Moreover, the dynamic motions departing from es ∼ c are smaller in amplitude than those arising from a centered condition (es/c = 0). The larger damping produced by a very small squeeze film thickness explains the difference in response amplitude. At a largely off-centered condition (es/c = 0.99) and a low excitation frequency (f < 40 Hz), intermittent contact between the damper journal and its housing occurs as evidenced by a large magnitude recorded dynamic pressure (on the order of MPa). For whirl motions around various static eccentricity positions, es/c = 0.0–0.75, the dynamic load covers a frequency range from 10 Hz to 100 Hz using either a single-frequency excitation or a sine-sweep frequency excitation with a slow growth rate ∼6.5 Hz/s to induce a quasi-steady-state response. The experimental procedure builds complex stiffness in the frequency domain for identification of SFD stiffness, damping, and added mass force coefficients, (K, C, M)SFD. For motions centered around small to large static eccentricities, es/c = 0–0.75, the identified (K, C, M)SFD coefficients from sine-sweep frequency dynamic loads coincide with those extracted from single-frequency dynamic load tests over the same frequency range. Short-length SFD theory predictions for damping coefficients agree with the experimental results. Predicted added mass or inertia coefficients, like the model, fall short of the target experimental magnitudes. The test results give practitioners the credence to certify the ability of a SFD to control rotor response amplitude during typical transient events.

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References

Cookson, R. A. , 1979, “ The Effectiveness of Squeeze-Film Damper Bearings Supporting Rigid Rotors Without a Centralising Spring,” Int. J. Mech. Sci., 21(11), pp. 639–650. [CrossRef]
Dede, M. , Dogan, M. , and Holmes, R. , 1985, “ The Damping Capacity of a Sealed Squeeze Film Bearing,” ASME J. Tribol., 107(7), pp. 411–418. [CrossRef]
Zeidan, F. Y. , Vance, J. M. , and San Andrés, L. , 1996, “ Design and Application of Squeeze Film Dampers in Rotating Machinery,” 25th Turbomachinery Symposium, Texas A&M University, Houston, TX, Sept. 17–19, pp. 169–188.
San Andrés, L. , Jeung, S.-H. , Den, S. , and Savela, G. , 2016, “ Squeeze Film Dampers: An Experimental Appraisal of Their Dynamic Performance,” 1st Asia Turbomachinery and Pump Symposium, Singapore, Feb. 22–25.
Della Pietra, L. , and Adiletta, G. , 2002, “ The Squeeze Film Damper Over Four Decades of Investigations. Part I: Characteristics and Operating Features,” Shock Vib. Dig., 34(1), pp. 3–26.
Adiletta, G. , and Della Pietra, L. , 2002, “ The Squeeze Film Damper Over Four Decades of Investigations. Part II: Rotordynamics Analysis With Rigid and Flexible Rotors,” Shock Vib. Dig., 34(2), pp. 97–126.
Pan, C. H. T. , and Tonessen, J. , 1978, “ Eccentric Operation of Squeeze-Film Damper,” ASME J. Lubr. Tech., 2(100), pp. 369–377. [CrossRef]
Cookson, R. A. , 1980, “ The Effectiveness of Squeeze-Film Damper Bearings Supporting Flexible Rotors Without a Centralising Spring,” Int. J. Mech. Sci., 22(5), pp. 313–324. [CrossRef]
Cookson, R. A. , 1981, “ The Vibration Isolating Properties of Uncentralized Squeeze-Film Damper Bearings Supporting a Flexible Rotor,” ASME J. Gas Turbines Power, 103(4), pp. 781–787. [CrossRef]
Den Hartog, J. P. , 1985 Mechanical Vibrations, Dover Publications, Mineola, NY, pp. 225–277.
Harish, C. N. , and Sekhar, A. S. , 2013, “ Swept Sine Testing of Rotor-Bearing System for Damping Estimation,” J. Sound Vib., 333(2), pp. 604–620.
San Andrés, L. , and Diaz, S. E. , 2001, “ Sine Sweep Load vs. Impact Excitations and Their Influence on the Damping Coefficients of a Bubbly Oil Squeeze Film Damper,” STLE Tribol. Trans., 44(4), pp. 692–698. [CrossRef]
Jeung, S.-H. , San Andrés, L. , and Bradley, G. , 2016, “ Forced Coefficients for a Short Length, Open-Ends Squeeze Film Damper With End Grooves: Experiments and Predictions,” ASME J. Gas Turbines Power, 138(2), p. 032502.
Den, S. , 2015, “ Analysis of Force Coefficients and Dynamic Pressures for Short-Length (L/D=0.2) Open-Ends Squeeze Film Dampers,” M.S. thesis, Texas A&M University, College Station, TX.
San Andrés, L. , 2012, “ Squeeze Film Damper: Operation, Models, and Technical Issues,” Modern Lubrication Theory, Notes 13, Texas A&M University, College Station, TX.
Zeidan, F. Y. , and Vance, J. M. , 1990, “ Cavitation and Air Entrainment Effects on the Response of Squeeze Film Supported Rotors,” ASME J. Tribol., 112(2), pp. 347–353. [CrossRef]
San Andrés, L. , and Jeung, S.-H. , 2016, “ Response of a Squeeze Film Damper-Elastic Structure System to Multiple and Consecutive Impact Loads,” ASME J. Eng. Gas Turbines Power (accepted).

Figures

Grahic Jump Location
Fig. 1

(a) Top view of SFD test rig, (b) schematic view of whirl orbit kinematics, (c) coordinate systems for motion, (d) various orbits with amplitude (r) and whirling around static eccentricity (es)

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Fig. 2

(a) View of journal with diameter D = 12.7 cm, land length, L = 2.54 cm (L/D = 0.2), three 120 deg spaced orifice feedholes ϕ = 2.54 mm, and (b) cross section of squeeze film with radial clearance c = 267 μm

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Fig. 3

Cut-section view of the SFD test bearing section, lubrication flow path, flexural support rods

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Fig. 4

Example of a recorded sine-sweep frequency dynamic load. Excitation frequency varies with α = 6.5 Hz/s.

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Fig. 5

Measured applied dynamic load components (FX, FY), ensuing BC displacements (x/c, y/c), and BC eccentricity (e/c) versus frequency (fr) for motions departing from es = 0 with Fs = 0 N and F* ≈ 110 N. Frequency range 5–245 Hz, α = 33 Hz/s.

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Fig. 6

Measured DFT amplitude of dynamic load (Fx) and displacement (x/c) from a sine-sweep frequency dynamic load excitation with α = 33, 40, 55 Hz/s over frequency range 5–245 Hz. Motions departing from es = 0, Fs = 0 N and dynamic load amplitude F* ≈ 110 N.

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Fig. 7

Experimental dynamic load components (FX, FY), ensuing BC displacements (x/c, y/c), and BC eccentricity (e/c) versus frequency (fr) for motions departing from es = 0.95 c with Fs = 2270 N and F*≈ 110 N. Frequency range 5–245 Hz, α = 33 Hz/s.

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Fig. 8

Measured DFT amplitude of BC displacements (x/c, y/c) from a sine-sweep frequency dynamic load excitation with α = 33 Hz/s over frequency range 5–245 Hz. Motions departing from es = 0 and 0.95 c (Fs = 2270 N), dynamic load amplitude F* ≈ 110 N.

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Fig. 9

(a) Frames of the measured dynamic load (FX versus FY) for various frequency fr = f/fn (fn = 122 Hz). Motions departing from es = 0.95 c with F*≈ 110 N and Fs = 2270 N. Frequency range 5–245 Hz, angular acceleration = 33 Hz/s. (b) Frames of measured BC whirl orbit motion (x/c versus y/c) for various frequency fr = f/fn (fn = 122 Hz). Motions departing from es = 0.95 c with F*≈110 N and Fs = 2270 N. Frequency range 5–245 Hz, angular acceleration = 33 Hz/s.

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Fig. 10

Recorded amplitude of applied dynamic load, dynamic film pressure P¯=P4/P*, and film thickness (h/c), versus frequency fr = f/fn (fn = 122 Hz). Data obtained for motions departing from static eccentricity es = 0.99 c with F* ≈ 110 N and Fs = 2360 N. Frequency range 5–20 Hz, α = 33 Hz/s.

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Fig. 11

Real and imaginary parts of measured direct complex stiffnesses (HXX, HYY) for the lubricated system (solid line) versus excitation frequency and corresponding K-C-M curve fits (dashed line). Data obtained from a sine-sweep frequency load with frequency range 10–110 Hz, α = 6.5 Hz/s.

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Fig. 12

Damping coefficients (C¯=C/C*)XX,YY versus static eccentricity (eS/c) obtained from sine-sweep frequency dynamic loads with α = 6.5 Hz/s and two single-frequency circular orbit tests, Frequency range 10–100 Hz. Predictions from short-length open-ends SFD model.

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Fig. 13

Added mass coefficients (M¯=M/M*)XX,YY versus static eccentricity (eS/c) obtained from sine-sweep frequency dynamic loads with α = 6.5 Hz/s and two single-frequency circular orbit tests, Frequency range 10–100 Hz. Predictions from short-length open-ends SFD model.

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Fig. 14

Stiffness coefficients (K¯=K/Ks)XX,YY versus static eccentricity (eS/c) obtained from sine-sweep frequency dynamic load tests with α = 6.5 Hz/s and two single-frequency circular orbit tests. Frequency range 10–100 Hz.

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Fig. 15

Recorded whirl orbit(s) from (left) sine-sweep frequency dynamic load excitation with α = 6.5 Hz/s and (right) single-frequency dynamic load excitation. Both show nearly equal orbit amplitude (r∼0.05c) over frequency range 10–100 Hz. Insets zoom in on the whirl orbit.

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