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Research Papers: Gas Turbines: Structures and Dynamics

Rotordynamics Performance of Hybrid Foil Bearing Under Forced Vibration Input

[+] Author and Article Information
Daejong Kim

Mechanical and Aerospace Engineering,
University of Texas at Arlington,
Arlington, TX 76019-0018
e-mail: daejongkim@uta.edu

Brian Nicholson, Lewis Rosado, Garry Givan

Aerospace System Directorate,
AFRL,
Wright Patterson AFB1790 Loop Road,
Dayton, OH 45433

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 July 5, 2017; final manuscript received July 5, 2017; published online September 19, 2017. Editor: David Wisler.

J. Eng. Gas Turbines Power 140(1), 012507 (Sep 19, 2017) (12 pages) Paper No: GTP-17-1286; doi: 10.1115/1.4037624 History: Received July 05, 2017; Revised July 05, 2017

Foil bearings (FB) are one type of hydrodynamic air/gas bearings but with a compliant bearing surface supported by structural material that provides stiffness and damping to the bearing. The hybrid foil bearing (HFB) in this paper is a combination of a traditional hydrodynamic foil bearing with externally pressurized air/gas supply system to enhance load capacity during the start and to improve thermal stability of the bearing. The HFB is more suitable for relatively large and heavy rotors where rotor weight is comparable to the load capacity of the bearing at full speed and extra air/gas supply system is not a major added cost. With 4448–22,240 N thrust class turbine aircraft engines in mind, the test rotor is supported by HFB in one end and duplex rolling element bearings (REB) in the other end. This paper presents experimental work on HFB with diameter of 102 mm performed at the U.S. Air force Research Laboratory (AFRL). Experimental works include: measurement of impulse response of the bearing to the external load corresponding to rotor's lateral acceleration of 5.55 g, forced response to external subsynchronous excitation, and high-speed imbalance response. A nonlinear rotordynamic simulation model was also applied to predict the impulse response and forced subsynchronous response. The simulation results agree well with the experimental results. Based on the experimental results and subsequent simulations, an improved HFB design is also suggested for higher impulse load capability up to 10 g and rotordynamics stability up to 30,000 rpm under subsynchronous excitation.

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Figures

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Fig. 1

Photo and cross-section model of AFRL test rig: (a) structure of HFB and bump (with top foil removed), (b) photos of HFB housing, REB and EMA, and (c) cross section of test rig

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Fig. 2

Coordinate system for 4DOF analysis; origin at the center of gravity. In all the plots, vertical direction is −X and horizontal direction is Y.

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Fig. 3

Measured load from load cell underneath EMA versus command signal from the controller

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Fig. 4

Temperature profile with continuous impulse loading, 12,000 rpm: (a) 1467 N impulse and (b) 1912 N impulse

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Fig. 5

Measured impulse response to loading in Fig. 3, all displacements from center of steady-state orbit. Arrows represent timing of loading and unloading: (a) transient response during loading and unloading, (b) detail view during loading, and (c) detail view during unloading.

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Fig. 6

Simulated impulse response to loading in Fig. 3, all displacements from center of steady-state orbit. Arrows represent timing of loading and unloading (a) during loading and (b) buring unloading.

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Fig. 7

Cross section of rig at the HFB location

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Fig. 8

Measured forced subsynchronous response to 50 Hz vertical excitation at 12,000 rpm, ±668 N plus rotor weight. The insert is an orbit with amplitude axis as a scale bar.

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Fig. 9

Simulated forced subsynchronous response to 50 Hz vertical excitation at 12,000 rpm, ±668 N plus rotor weight: (a) Nonlinear model and (b) Using linear coefficients of HFB

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Fig. 10

Measured forced subsynchronous response to 80 Hz vertical excitation at 12,000 rpm, ±668 N plus rotor weight. The insert is an orbit with amplitude axis as a scale bar.

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Fig. 11

Measured forced subsynchronous response to 110 Hz vertical excitation at 12,000 rpm, ±668 N plus rotor weight. The insert is an orbit with amplitude axis as a scale bar.

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Fig. 12

Measured forced subsynchronous response to 130 Hz vertical excitation at 12,000 rpm, ±668 N plus rotor weight. The insert is an orbit with amplitude axis as a scale bar.

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Fig. 13

Forced subsynchronous response to 120 Hz vertical excitation at 15,000 rpm, ±668 N plus rotor weight. The insert is an orbit with amplitude axis as a scale bar.

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Fig. 14

Forced subsynchronous response to 120 Hz horizontal excitation at 15,000 rpm, ±668 N plus rotor weight. The insert is an orbit with amplitude axis as a scale bar: (a) experiment and (b) simulation.

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Fig. 15

Forced subsynchronous response to 120 Hz horizontal excitation at 18,000 rpm, ±668 N plus rotor weight. The insert is an orbit with amplitude axis as a scale bar: (a) experiment and (b) simulation.

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Fig. 16

Detail view of Fig. 15 in frequency range 10–20 krpm: (a) experiment and (b) simulation

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Fig. 17

Cascade plot from measured imbalance response at 8000–24,000 rpm: (a) horizontal direction and (b) vertical direction

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Fig. 18

Simulated response to 10 g loading/unloading in vertical direction at different speeds, tenfold increase of bump stiffness, C = 200 μm, rp = 120 μm: (a) during loading and (b) during unloading

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Fig. 19

Simulated forced subsynchronous response to 120 Hz horizontal excitation, ±668 N, tenfold increase of bump stiffness, C = 200 μm, rp = 120 μm: (a) horizontal and (b) vertical

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Fig. 20

Simulated forced subsynchronous response to 120 Hz vertical excitation, ±668 N, tenfold increase of bump stiffness, C = 200 μm, rp = 120 μm

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