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Research Papers: Gas Turbines: Structures and Dynamics

On the Force Coefficients of a Flooded, Open Ends Short Length Squeeze Film Damper: From Theory to Practice (and Back)

[+] Author and Article Information
Luis San Andrés

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

Sean Den

Texas A&M University,
College Station, TX 77843
e-mail: Sean.thewind@yahoo.com

Sung-Hwa Jeung

Texas A&M University,
College Station, TX 77843
e-mail: Sean.jeung@gmail.com

1Presently at Formosa Plastics Corporation, Point Comfort, TX 77978.

2Presently at Compressor Technology and Development, Ingersoll Rand, La Crosse, WI 54601.

3Corresponding author.

Contributed by the Structures and Dynamics Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received July 2, 2017; final manuscript received July 5, 2017; published online September 19, 2017. Editor: David Wisler.

J. Eng. Gas Turbines Power 140(1), 012502 (Sep 19, 2017) (11 pages) Paper No: GTP-17-1250; doi: 10.1115/1.4037585 History: Received July 02, 2017; Revised July 05, 2017

Gas turbine aircraft engine manufacturers push for simple squeeze film damper (SFD) designs, short in length, yet able to provide enough damping to ameliorate rotor vibrations. SFDs employ orifices to feed lubricant directly into the film land or into a deep groove. The holes, acting as pressure sources (or sinks), both disrupt the film land continuity and reduce the generation of squeeze film dynamic pressure. Overly simple predictive formulations disregard the feedholes and deliver damping (C) and inertia (M) force coefficients not in agreement with experimental findings. Presently, to bridge the gap between simple theory and practice, the paper presents measurements of the dynamic forced response of an idealized SFD that disposes of the feedholes altogether. The short-length SFD, whose diameter D = 127 mm, has one end submerged (flooded) within a lubricant bath and the other end exposed to ambient. ISO VG 2 lubricant flows by gravity through the film land of length L = 25.4 mm and clearance c = 0.122 mm. From dynamic load tests over excitation frequency range 10–250 Hz, experimental damping coefficients (CXX, CYY) from the flooded damper agree well with predictions from the classical open ends model with a full film for small amplitude whirl motions (r/c ≪ 1), centered and off-centered. Air ingestion inevitably occurs for large amplitude motions (r/c > 0.4), thus exacerbating the difference between predictions and tests results. For reference, identical tests were conducted with a practical SFD supplied with lubricant (Pin = 0.4 bar) via three orifice feedholes, 120 deg apart at the film land midplane. A comparison of test results shows as expected that, for small amplitude (r/c ∼ 0.05) orbits, the flooded damper generates on average 30% more damping than the practical configuration as the latter's feedholes distort the generation of pressure. For large amplitude motions (r/c > 0.4), however, the flooded damper provides slightly lesser damping and inertia coefficients than the SFD with feedholes whose pressurized lubricant delivery alleviates air ingestion in the film land. The often invoked open ends SFD classical model is not accurate for the practical engineered design of an apparently simple mechanical element.

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References

San Andrés, L. , 2012, “ Modern Lubrication Theory, Squeeze Film Damper: Operation, Models and Technical Issues, Notes 13,” Texas A&M University Digital Libraries, College Station, TX. http://rotorlab.tamu.edu/me626/Notes_pdf/Notes13%20Squeeze%20Film%20Dampers.pdf
Vance, J. M. , 1988, Rotordynamics of Turbomachinery, Wiley, Hoboken, NJ, Chap. 6.
Harnoy, A. , 2002, Bearing Design in Machinery: Engineering Tribology and Lubrication, CRC Press, Boca Raton, FL, Chap. 18. [CrossRef]
Zeidan, F. , San Andrés, L. , and Vance, J. , 1996, “ Design and Application of Squeeze Film Dampers in Rotating Machinery,” 25th Turbomachinery Symposium, Houston, TX, Sept. 16–19, pp. 169–188. http://turbolab.tamu.edu/proc/turboproc/T25/T25169-188.pdf
San Andrés, L. , and Jeung, S.-H. , 2015, “ Experimental Performance of an Open Ends, Centrally Grooved, Squeeze Film Damper Operating With Large Amplitude Orbital Motions,” ASME J. Eng. Gas Turbines Power, 137(3), p. 032508. [CrossRef]
Jeung, S.-H. , San Andrés, L. , and Bradley, G. , 2015, “ Forced Coefficients for a Short Length, Open-Ends Squeeze Film Damper With End Grooves: Experiments and Predictions,” ASME J. Eng. Gas Turbines Power, 138(2), p. 022501. [CrossRef]
San Andrés, L. , and Jeung, S.-H. , 2016, “ Orbit-Model Force Coefficients for Fluid Film Bearings: A Step Beyond Linearization,” ASME J. Eng. Gas Turbines Power, 138(2), p. 022502. [CrossRef]
San Andrés, L. , Jeung, S.-H. , Den, S. , and Savela, G. , 2016, “ Squeeze Film Damper: An Experimental Appraisal of Their Dynamic Performance,” Asia Turbomachinery and Pump Symposium (ATPS), Singapore, Feb. 22–26, pp. 1–23. http://rotorlab.tamu.edu/tribgroup/2016%20TRC%20San%20Andres/2016%20ATPS%20SFD%20paper.pdf
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, “ Modern Lubrication Theory, Liquid Cavitation in Fluid Film Bearings, Notes 6,” Texas A&M University Digital Libraries, College Station, TX. http://rotorlab.tamu.edu/me626/Notes_pdf/Notes06%20Liquid%20cavitation%20model.pdf
Diaz, S. , and San Andrés, L. , 2001, “ A Model for Squeeze Film Dampers Operating With Air Entrainment and Validation With Experiments,” ASME J. Tribol., 123(1), pp. 125–133. [CrossRef]
Diaz, S. , and San Andrés, L. , 2001, “ Air Entrainment Versus Lubricant Vaporization in Squeeze Film Dampers: An Experimental Assessment of Their Fundamental Differences,” ASME J. Eng. Gas Turbines Power, 123(4), pp. 871–877. [CrossRef]
Gehannin, J. , Arghir, M. , and Bonneau, O. , 2015, “ A Volume of Fluid Method for Air Ingestion in Squeeze Film Dampers,” Tribol. Trans., 59(2), pp. 208–218. [CrossRef]
Adiletta, G. , and Della Pietra, L. , 2006, “ Experimental Study of a Squeeze Film Damper With Eccentric Circular Orbits,” ASME J. Tribol., 128(2), pp. 365–377. [CrossRef]
Pan, C. H. T. , and Tonessen, J. , 1978, “ Eccentric Operation of Squeeze-Film Damper,” J. Lubr. Technol., 100(3), pp. 369–377. [CrossRef]
Fritzen, C. P. , 1986, “ Identification of Mass, Damping, and Stiffness Matrices of Mechanical System,” J. Vib., Acoust., Stress, and Reliab., 108(1), pp. 9–16. [CrossRef]

Figures

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Fig. 1

SFD test rig with damper structure, electromagnetic shakers, and a static loader (inset shows a top view of test rig)[7]

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Fig. 2

(a) Cross section of BC and lubricant flow path and (b) photograph of journal submerged in a lubricant bath

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Fig. 3

Schematic views (side and top) of the lubricant flow path through the film clearance for (left) flooded damper, and (right) damper with (three) feedholes at midplane

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Fig. 4

Open-ends flooded damper (c = 122 μm): direct and cross-coupled damping coefficients (C¯XX, C¯XY)SFD versus static eccentricity (es/c) and orbit amplitude (r/c)

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Fig. 5

Open-ends flooded damper (c = 122 μm): direct and cross-coupled added mass coefficients (M¯XX, M¯XY)SFD versus static eccentricity (es/c) and orbit amplitude (r/c)

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Fig. 6

Open-ends flooded damper (c = 122 μm): direct and cross-coupled stiffness coefficients (−K¯XX, −K¯XY)SFD versus static eccentricity (es/c) and orbit amplitude (r/c). Coefficients normalized by structural stiffness KS.

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Fig. 7

Test damping (C¯XX, C¯YY) coefficients (a) versus whirl orbit amplitude (r/c) about center (es = 0) and (b) versus static eccentricity (es/c) for orbits with r = 0.05c. Predictions from orbit model [7] and full-film lubrication theory [1].

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Fig. 8

Test added mass (M¯XX, M¯YY) coefficients (a) versus whirl orbit amplitude (r/c) about center (es = 0) and (b) versus static eccentricity (es/c) for orbits with r = 0.05c. Predictions from orbit model [7] and full-film lubrication theory [1].

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Fig. 9

Test damping (C¯XX, C¯YY) and added mass (M¯XX, M¯YY) coefficients versus whirl orbit amplitude (r/c) at static eccentricity es = 0.15c. Predictions from orbit model [7].

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Fig. 10

Schematic views of pressure sensors disposition in bearing: (a) top, (b) axial, and (c) unwrapped views [6]

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Fig. 11

Photograph of bottom oil collector showing lubricant discharge condition as a foamy mixture

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Fig. 12

Open-ends flooded damper: dynamic film pressure (P4) and film thickness (h) recorded at midplane location. Circular centered orbit with amplitude r/c = 0.45 and whirl frequency f = 100 Hz and 200 Hz. Clearance c = 122 μm.

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Fig. 13

Open-ends flooded damper: dynamic film pressure (P4) and film thickness (h) recorded at midplane. Motions centered at es = 0 and 0.15 c with amplitude r/c = 0.60, whirl frequency f = 200 Hz. c = 122 μm.

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Fig. 14

Open-ends flooded damper: Measured peak–peak film pressure (P¯) at midplane versus squeeze velocity (vs). Circular centered whirl motions. Frequency range: 50–200 Hz. Orbit radii r = 0.05 c to 0.60 c. (Inset shows location of pressure sensor and journal position relative to the BC.)

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Fig. 15

Flooded SFD and orifice fed SFD: experimental damping coefficients (C¯XX, C¯YY) (a) versus whirl orbit amplitude (r/c) about center (es = 0) and (b) versus static eccentricity (es/c) for orbits with r = 0.05 c

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Fig. 16

Flooded SFD and orifice fed SFD: experimental inertia coefficients (M¯XX, M¯YY) (a) versus whirl orbit amplitude (r/c) about center (es = 0) and (b) versus static eccentricity (es/c) for orbits with r = 0.05 c

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