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Research Papers: Gas Turbines: Controls, Diagnostics, and Instrumentation

Synthesis of Experimental and Theoretical Analysis of Pneumatic Hammer Instability in an Aerostatic Bearing

[+] Author and Article Information
Mihai Arghir

PPRIME Institute,
UPR CNRS 3346,
Université de Poitiers, ENSMA ISAE, Chasseneuil Futuroscope 86962, France

Mohamed-Amine Hassini, Franck Balducchi

Centre National d'Etudes Spatiales,
PPRIME Institute,
Université de Poitiers,
Poitiers 86000, France

Romain Gauthier

SNECMA,
Division Moteurs Spatiaux,
Vernon 27208, France

1Present address: EDF Recherche et Développement, Clamart 92141, France.

2Present address: Hutchinson Stop-Choc Ltd., Banbury Avenue, Slough SL1 4LR, UK.

Contributed by the Controls, Diagnostics and Instrumentation Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received July 20, 2015; final manuscript received August 5, 2015; published online September 1, 2015. Editor: David Wisler.

J. Eng. Gas Turbines Power 138(2), 021602 (Sep 01, 2015) (8 pages) Paper No: GTP-15-1346; doi: 10.1115/1.4031322 History: Received July 20, 2015

The present work is focused on the pneumatic hammer instability in an aerostatic bearing with shallow recesses and orifices of four different diameters. Operating conditions were zero rotation speed, zero load, and different supply pressures. The diameters of the tested orifices were large compared to the usual practice and correspond to a combined inherent and orifice restriction. The theoretical analysis was based on the computational fluid dynamics (CFD) evaluation of the ratio between the recess and the feeding pressure and on the “bulk flow” calculation of the rotordynamic coefficients of the aerostatic bearing. Calculations showed an increase of the direct stiffness with decreasing the orifice diameter and increasing the supply pressure and, on the other hand, a decrease toward negative values of the direct damping with decreasing the orifice diameter. These negative values of the direct damping coefficient indicate pneumatic hammer instabilities. In parallel, experiments were performed on a floating bearing test rig. Direct stiffness and damping coefficients were identified from multiple frequency excitations applied by a single shaker. Experiments were performed only for the three largest orifices and confirmed the decrease of the direct damping with the orifice diameter and the supply pressure. The identification of the rotordynamic coefficients was not possible for the smallest available orifice because the aerostatic bearing showed self-sustained vibrations for all feeding pressures. These self-sustained vibrations are considered the signature of the pneumatic hammer instability. The paper demonstrates that aerostatic bearings with shallow recesses and free of pneumatic hammer instabilities can be designed by adopting orifice restrictors of large size diameter.

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References

Rieger, N. F., ed., 1967, Design of Gas Bearings Notes (note supplemetal to the RPI-MTI Course on Gas Bearing Design, Aug. 14), Vol. 2, Rensselaer Polytechnic Institute, Troy, NY, and Mechanical Technology, Inc., Latham, NY.
Powell, J. W. , 1970, Design of Aerostatic Bearings, The Machinery Publishing, Brighton, UK.
Gross, W. A. , Matsch, L. A. , Castelli, V. , Eshel, A. , Vohr, J. H. , and Wildmann, M. , 1980, Fluid Film Lubrication, Wiley-Interscience, New York.
Fuller, D. D. , 1984, Theory and Practice of Lubrication for Engineers, 2nd ed., Wiley, New York.
Hassini, M. A. , Arghir, M. , and Frocot, M. , 2012, “ Comparison Between Numerical and Experimental Dynamic Coefficients of a Hybrid Aerostatic Bearing,” ASME J. Eng. Gas Turbines Power, 134(12), p. 122506. [CrossRef]
Hassini, M. A. , 2012, “ Contribution à l'analyse des paliers fluids et des joints d’étanchéité utilisés dans les turbopompes spatiales,” Thèse de Docteur de l'Université de Poitiers, Poitiers, France.
Arghir, M. , and Frêne, J. , 2001, “ Numerical Solution of Lubrication's Compressible Bulk Flow Equations: Applications to Annular Gas Seals Analysis,” ASME Paper No. 2001-GT-117.
Roblee, J. W. , 1985, “ Design of Externally Pressurized Gas Bearings for Dynamic Applications,” Ph.D. dissertation, University of California, Berkley, CA.
Arghir, M. , 2011, “ Butée et paliers aérostatiques,” Techniques de l'Ingénieur, Report No. BM 5 336.
Arghir, M. , Balducchi, F. , Hassini, M. A. , Guingo, S. , and Renard, E. , 2013, “ Theoretical and Experimental Analysis of the Pneumatic Hammer Instability in an Aerostatic Bearing,” 5th World Tribology Congress (WTC 2013), Torino, Italy, Sept. 8–13, p. 1016.

Figures

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Fig. 1

Aerostatic hybrid bearings

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Fig. 2

Inertia effects in an aerostatic bearing

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Fig. 3

Boundary conditions for CFD analysis

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Fig. 4

Restrictor flow streaklines

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Fig. 5

Comparisons between CFD and bulk flow results (axial direction)

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Fig. 6

Amplitude (a) and phase (b) of the first-order recess pressure

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Fig. 7

Amplitude (a) and phase (b) of the first-order mass flow rate

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Fig. 8

The geometry of the circular aerostatic thrust bearing

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Fig. 9

Static stiffness of the circular aerostatic thrust bearing

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Fig. 10

Damping of the circular aerostatic thrust bearing for an infinite mass (i.e., ω → 0)

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Fig. 11

Variation of the recess pressure

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Fig. 12

Contour plot of the theoretical direct static stiffness K0 (N/m)

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Fig. 13

Contour plot of the theoretical direct damping C (N/m) for ω → 0

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Fig. 14

Side view of the floating bearing test rig

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Fig. 15

Front view of the floating bearing

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Fig. 16

Contour plot (continuous black lines) of the measured direct stiffness (N/m)

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Fig. 17

Contour plot (continuous black lines) of the measured direct damping (N s/m)

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Fig. 18

Power spectrum of measured acceleration for 50%Dorifice and for different supply pressures

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