Research Papers: Gas Turbines: Structures and Dynamics

Response of a Squeeze Film Damper-Elastic Structure System to Multiple and Consecutive Impact Loads

[+] 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

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

1Corresponding 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 13, 2016; final manuscript received June 19, 2016; published online August 2, 2016. Editor: David Wisler.

J. Eng. Gas Turbines Power 138(12), 122504 (Aug 02, 2016) (12 pages) Paper No: GTP-16-1214; doi: 10.1115/1.4034001 History: Received June 13, 2016; Revised June 19, 2016

Squeeze film dampers (SFDs) are common in aircraft gas turbine engines, customized to provide a desired level of damping while also ensuring structural isolation. This paper presents measurements obtained in a test rig composed of a massive cartridge, an elastic structure, and an open-ends SFD with length L = 25.4 mm, diameter D = 127 mm, and radial clearance c = 0.267 mm. ISO VG 2 oil at room temperature lubricates the thin film. The measurements quantify the system transient response to sudden loads for motions departing from various static eccentricity displacements, es/c = 0–0.6. The batch of tests include recording the system response to (a) one single impact, (b) two (and three) impacts with an elapsed time of 30 ms in between, and (c) two or more consecutive impacts, without any delay, each with a load magnitude at 50% of the preceding impact. The load actions intend to reproduce, for example, a hard landing on an uneven surface or plunging motions from sudden contacts in a machine tool. The test system transient responses due to one or more impacts, each 30 ms apart, show the peak amplitude of motion (ZMAX) is proportional to the magnitude of applied load (FMAX). The identified system damping ratio (ξ) is proportional to the peak dynamic displacement as a linear system would show. Predictions of transient response from a physical SFD model accounting for fluid inertia correlate best with the experimental results as they produce greatly reduced peak dynamic motions when compared to predictions from a purely viscous SFD model. For the responses due to consecutive impacts, one after the other with no delay, the system motion does not decay immediately but builds to produce larger motion amplitudes than in the earlier cases. Eventually, as expected, after several oscillations, the system comes to rest. For an identical damper having a smaller clearance cs = 0.213 mm (0.8c), its damping ratio (ξs) is ∼1.3 to ∼1.7 times greater than the damping ratio for the damper with a larger film clearance (ξ). Hence, the experimentally derived (ξs/ξ) scales with (c/cs)2. The finding demonstrates the importance of manufacturing precisely the components in a damper to produce an accurate clearance.

Copyright © 2016 by ASME
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Fig. 1

(a) Photograph of the SFD test rig with shakers, static loader, and oil supply line (inset shows view from the top) and (b) cross section view of test SFD with lubricant flow path (L = 25.4 mm, D = 126.7 mm, c = 0.267 mm)

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Fig. 2

Journal with three orifices ϕ = 2.5 mm, 120 deg apart. Film land length, L = 25.4 mm, D = 126.7 mm. (L/D = 0.2).

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Fig. 3

Schematic view of BC statically displaced relative to a stationary journal (exaggerated film clearance)

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Fig. 4

Typical impact load along X direction and BC dynamic displacement ZX versustime. Test at centered condition (eS = 0.0c). Single impact load FMAX-X/(LD) = 2.4 bar → |ZMAX-X|/c = 0.17. Amplitude of DFT (ZX) shown.

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Fig. 5

Maximum displacements Z¯MAX/c versus peak load F¯MAX/(LD) for motions initiating from static eccentricity es/c = 0.0, 0.2, 0.4, and 0.6. Response to a single impact. β (1/bar) = slope of linear fit to data. Open-ends SFD with clearance c = 0.267 mm.

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Fig. 6

Peak BC dynamic amplitude |ZX|MAX/c and envelope (e−ξωnt) versus time (t). Measurements for FMAX/(LD) = 2.4 bar and 6.1 bar for motions from es = 0, and for FMAX/(LD) = 5.4 bar for motions from es = 0.6c. Amplitude of DFT (ZX) also shown. (a) ZX(t) and (b) ZX(ω).

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Fig. 7

System damping ratio (ξ) and logarithmic decrement (δ) versus peak displacement (ZMAX/c). Data for one impact load and motions departing from various static eccentricity. Open-ends SFD with c = 0.267 mm (L/D = 0.2).

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Fig. 8

SFD damping ratio (ξ) versus peak BC (ZMAX/c) displacement. Open-ends SFD with c = 0.267 mm and cs = 0.213 mm [20]. Parameters identified for motions initiating at static eccentricity es/c = 0.

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Fig. 9

Sets of consecutive (3 and 6) impact loads FX(t) and ensuing BC displacements ZX(t) versus time. Measurements for FMAX-X/(LD) ∼ 3.1 bar and motions initiating from static eccentricity es = 0. Elapsed time between impacts ti ∼ 30 ms. (a) impact F versus time and (b) response Z versus time.

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Fig. 10

Maximum displacement Z¯MAX/c versus peak load F¯MAX/(LD) for motions from es = 0. Data from six consecutive impacts with elapsed time between impacts ti ∼ 30 ms. (Insets show time traces of impact load and ensuing BC displacement). β (1/bar) = slope of line fit to data.

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Fig. 11

β = slope of Z¯MAX/cversusF¯MAX/(LD) versus number of impacts for motions initiating from es = 0. Tests with consecutive impacts, one to six. Average elapsed time between impacts ti = ∼30 ms. Open-end SFD clearance c = 0.267 mm.

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Fig. 12

Impact load FX(t) and ensuing BC displacement ZX(t) versus time for (a) single impact, (b) 3¯ consecutive impacts, and (c) 4¯ consecutive impacts. Elapsed time between impacts is ti = ∼0 s. Motions departing from es = 0 and FMAX/(LD) = 7.9 bar.

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Fig. 13

(Normalized) impact load and BC displacement and velocity versus time for motions from es = 0. Graphs shows data for 4¯ consecutive and immediate impacts for FMAX/(LD) = 7.8 bar. Elapsed time between impacts is ti = ∼0 s.

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Fig. 14

Maximum displacement Z¯MAX/c versus peak load F¯MAX/(LD) for motions from es = 0 (left) and es = 0.4c (right). Tests with (a) case 3¯ and (b) case 4¯ consecutive impacts; elapsed time between impacts ti = 0 s. β (1/bar) = slope of line fit to data. Open-ends SFD c = 0.267 mm.

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Fig. 15

β = slope of Z¯MAX/cversusF¯MAX/(LD) versus static eccentricity (es/c). Tests with one, 3¯ and 4¯ consecutive impacts;elapsed time between impacts ti = 0 ms. Open-end SFD c = 0.267 mm.

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Fig. 16

Experimental and predicted β = slope of Z¯MAX/cversusF¯MAX/(LD) versus number of impacts for motions from es = 0. Duration of impact tIMP = 1.3 ms and elapsed time in between impacts ti = 30 ms. Predictions without and with fluid inertia in the SFD model. Open-ends SFD c = 0.267 mm.




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