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Research Papers: Gas Turbines: Structures and Dynamics

Forced Coefficients for a Short Length, Open Ends Squeeze Film Damper With End Grooves: Experiments and Predictions

[+] Author and Article Information
Sung-Hwa Jeung

Mechanical Engineering Department,
Texas A&M University,
College Station, TX 77843
e-mail: sean.jeung@gmail.com

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

Gary Bradley

Motor Trike, Inc.,
Troup, TX 75789
e-mail: g-daniel@sbcglobal.net

1Corresponding author.

2Work conducted as a 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 23, 2015; final manuscript received July 23, 2015; published online September 1, 2015. Editor: David Wisler.

J. Eng. Gas Turbines Power 138(2), 022501 (Sep 01, 2015) (11 pages) Paper No: GTP-15-1216; doi: 10.1115/1.4031236 History: Received June 23, 2015

Squeeze film dampers (SFDs) are effective to ameliorate shaft vibration amplitudes and to suppress instabilities in rotor–bearing systems. Compact aero jet engines implement ultra-short length SFDs (L/D ≤ 0.2) to satisfy stringent weight and space demands with low parts count. This paper describes a test campaign to identify the dynamic forced response of an open ends SFD (L = 25.4 mm and D = 125.7 mm), single film land, and oil fed through three holes (120 deg apart), operating with similar conditions as in an aircraft engine. Two journals make for two SFD films with clearances cA = 0.129 mm and cB = 0.254 mm (small and large). The total oil-wetted length equals Ltot = 36.8 mm that includes deep end grooves, width and depth = 2.5 × 3.8 mm, for installation of end seals. In the current experiments, the end seals are not in place. A hydraulic static loader pulls the bearing cartridge (BC) to a preset static eccentricity (eS), and two electromagnetic shakers excite the BC with single frequency loads to create circular orbits, centered and off-centered, over a prescribed frequency range ω = 10–100 Hz. The whirl amplitudes range from r = 0.05cA–0.6cA and r = 0.15cB–0.75cB while the static eccentricity increases to eS = 0.5cA and eS = 0.75cB, respectively. Comparisons of force coefficients between the two identical dampers with differing clearances show that the small clearance damper (cA) provides ∼4 times more damping and ∼1.8 times the inertia coefficients than the damper with large clearance (cB). The test results demonstrate damping scales with ∼1/c3 and inertia with ∼1/c, as theory also showed. Analysis of the measured film land pressures evidence that the deep end grooves contribute to the generation of dynamic pressures enhancing the dynamic forced response of the test SFDs. A thin film flow model with an effective groove depth delivers predictions that closely match the test damping and inertia coefficients. Other predictions, based on the short length bearing model, use an effective length Leff ∼ 1.17L to deliver damping coefficients 15% larger than the experimental results; however, inertia coefficients are ½ of the identified magnitudes. The experiments and analysis complement earlier experimental work conducted with centrally grooved SFDs.

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Copyright © 2016 by ASME
Topics: Dampers , Damping
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References

Figures

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Fig. 8

Open ends dampers A and B: normalized dynamic film pressures (P̂) and film thickness (h) recorded at Θ = 225 deg versus time (t/T) for measurements at midplane (z = 0). Circular centered orbits with frequency ω = 200 Hz. Graphs show data for dampers A and B operating with orbit radii r = 38 μm and 76 μm.

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Fig. 7

Schematic views of the disposition of pressure sensors in BC: (a) top view, (b) axial view, and (c) unwrapped view [16]. (Figures 7(a) and 7(b) are reproduced with permission from San Andrés et al. [17]. Copyright 2014 by Springer International Publishing.)

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Fig. 6

SFD normalized coefficients for dampers A and B: direct damping (ĈXX,ĈYY) and added mass (M̂XX,M̂YY) coefficients versus orbit amplitude (r). Clearances cA = 129 μm and cB = 254 μm. Parameters identified at centered condition, eS/c = 0.0. (Reproduced with permission from San Andrés et al. [17]. Copyright 2014 by Springer International Publishing.)

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Fig. 5

Open ends damper B (cB = 254 μm): SFD direct and cross-coupled dynamic force coefficients (C¯B, M¯B, K¯B)SFD versus orbit amplitude (r/cB) at five static eccentricities (es/cB = 0.15, 0.30, 0.45, 0.60, 0.75). Identification frequency range 10–100 Hz. (Reproduced with permission from San Andrés et al. [17]. Copyright 2014 by Springer International Publishing.)

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Fig. 4

Open ends damper A (cA = 129 μm): SFD direct and cross-coupled dynamic force coefficients (C¯A, M¯A, K¯A)SFD versus orbit amplitude (r/cA) at five static eccentricities (es/cA = 0, 0.1, 0.2, 0.3, 0.4, 0.5). Identification frequency range 10–100 Hz [16]. (Reproduced with permission from San Andrés et al. [17]. Copyright 2014 by Springer International Publishing.)

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Fig. 3

(a) Cross section of SFD journal and BC showing the film land length (L) and side end grooves and lip sections. Total wetted length Ltot was noted. (b) Photograph of feed orifice with hex socket. (Figure 3(a) is reproduced with permission from San Andrés et al. [17]. Copyright 2014 by Springer International Publishing.)

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Fig. 2

SFD test rig schematic: (a) cut view and (b) top view with physical dimensions and path of lubricant flow (L = 25.4 mm, D = 127 mm, and cA = 129 μm or cB = 254 μm). (Figure 2(a) is reproduced with permission from San Andrés et al. [17]. Copyright 2014 by Springer International Publishing.)

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Fig. 1

Photograph of SFD test rig with components labeled. Inset shows view from the top. (Reproduced with permission from San Andrés et al. [17]. Copyright 2014 by Springer International Publishing.)

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Fig. 9

Normalized p–p film dynamic pressures versus excitation frequency (ω) for (a) open ends damper A [16] and (b) damper B. Centered (es = 0) circular orbit tests with radius r = 38 μm. Measurements at damper midplane, top and bottom (half-planes), and end grooves. (Inset shows location of pressure sensors). (Reproduced with permission from San Andrés et al. [17]. Copyright 2014 by Springer International Publishing.)

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Fig. 10

Normalized p–p film dynamic pressures (P4) at midplane (z = 0) versus whirl frequency (ω) for increasing orbit radii (r): (a) damper A and (b) damper B. Centered condition (eS = 0).

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Fig. 11

Open ends damper A (cA = 129 μm): experimental and predicted SFD direct damping and added mass coefficients (C¯A,M¯A)SFD versus amplitude (r/cA) for circular centered (eS = 0) orbits. Frequency range 10–100 Hz.

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Fig. 12

Open ends damper B (cB = 254 μm): experimental and predicted SFD direct damping and added mass coefficients (C¯B,M¯B)SFD versus amplitude (r/cB) for circular centered orbits (eS = 0). Frequency range 10–100 Hz.

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