Research Papers

Experimental Analysis of the Unbalance Response of Rigid Rotors Supported on Aerodynamic Foil Bearings

[+] Author and Article Information
Franck Balducchi

Hutchinson Stop-Choc Ltd.,
Banbury Avenue,
Slough SL1 4LR, UK
e-mail: fbalducchi@stop-choc.co.uk

Mihai Arghir

Fellow ASME
Institut PPRIME,
UPR CNRS 3346,
Université de Poitiers,
11. Bd. Pierre et Marie Curie,
Futuroscope 86962, Chasseneuil Cedex, France
e-mail: mihai.arghir@univ-poitiers.fr

Romain Gauthier

Space Engine Division,
Forêt de Vernon—BP 802,
Vernon 27208, France
e-mail: romain.gauthier@snecma.fr

1The work was performed at Institut PPRIME, UPR CNRS 3346, France, while being employed by Centre National d'Etudes Spatiales and by CNRS, respectively.

2Corresponding author.

Contributed by the Technical Committee on Vibration and Sound of ASME for publication in the JOURNAL OF VIBRATION AND ACOUSTICS. Manuscript received November 21, 2014; final manuscript received June 11, 2015; published online October 6, 2015. Assoc. Editor: John Yu.

J. Vib. Acoust 137(6), 061014 (Oct 06, 2015) (11 pages) Paper No: VIB-14-1443; doi: 10.1115/1.4031409 History: Received November 21, 2014; Revised June 11, 2015

The paper presents the experimental unbalance response of two slightly different rigid rotors supported by aerodynamic foil bearings. Impulse (Pelton) turbines manufactured directly in the mass of the rotors (on the outer surface) entrain both rotors at rotation speeds comprised between 50 krpm and 100 krpm. The displacements in the two foil bearings are measured during coast down and are depicted as waterfall plots. They show typical nonlinear behavior, i.e., subsynchronous vibrations accompanying the synchronous component. The measurements clearly show that the subsynchronous components bifurcate or jump at typical rotation speeds (mostly rational fractions of the rotation speed). The nonlinear behavior of the rigid rotor supported on foil bearings is also emphasized by varying the added unbalance: with increasing unbalance the vibration spectrum becomes gradually more diverse as new subsynchronous vibrations appear. The experimental results are compared with very simplified theoretical predictions based on the assumption that the air film in the two bearings is infinitely stiff compared to the foil structure. The latter is characterized by a cubic stiffness and a structural damping coefficient. The comparisons show only a rough qualitative agreement.

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Fig. 7

Waterfall plots of rotor 1 measured by the X displacement transducer at bearing 1

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Fig. 8

Waterfall plots of rotor 1 measured by the Y displacement transducer at bearing 2

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Fig. 6

Bearing temperatures for the rotor 1

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Fig. 3

Eigenfrequencies of the direct rigid modes of the rotors

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Fig. 2

Generation two foil bearing

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Fig. 1

Slice view of the test rig

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Fig. 5

Experimental static force/displacement (P1 = bearing 1, P2 = bearing 2)

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Fig. 4

The mounting for measuring the static stiffness of the foil bearings

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Fig. 9

Peak-to-peak amplitudes of rotor 1 (X direction in bearing 1 and Y direction in bearing 2)

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Fig. 10

Synchronous unbalance response of rotor 1 (X direction in bearing 1 and Y direction in bearing 2)

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Fig. 11

Bearing temperatures for rotor 2

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Fig. 12

Waterfall plots of rotor 2, residual unbalance

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Fig. 13

Waterfall plots of rotor 2 with 5 g mm added unbalance

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Fig. 14

The 4DOF rigid rotor supported on two bearings

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Fig. 15

Theoretical waterfall plots of the X displacements for the rotor 1 with 5 g mm unbalance



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