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Research Papers: Hydrodynamic Lubrication

Dynamic Force Coefficients of Hydrostatic Gas Films for Recessed Flat Plates: Experimental Identification and Numerical Predictions

[+] Author and Article Information
Adolfo Delgado

Texas A&M University,
Mechanical Engineering Department,
College Station, TX 77840
e-mail: adelgado@tamu.edu

Bugra Ertas

GE Global Research Center,
Mechanical Systems Organization,
1 Research Circle,
Niskayuna, NY 12309
e-mail: ertas@ge.com

Contributed by the Tribology Division of ASME for publication in the JOURNAL OF TRIBOLOGY. Manuscript received July 31, 2017; final manuscript received April 26, 2018; published online May 21, 2018. Assoc. Editor: Daejong Kim.

J. Tribol 140(6), 061703 (May 21, 2018) (9 pages) Paper No: TRIB-17-1305; doi: 10.1115/1.4040114 History: Received July 31, 2017; Revised April 26, 2018

The following paper focuses on an experimental and analytical study aimed at identifying the dynamic force coefficients of hydrostatic gas films for recessed flat plates. The motivation for the effort was brought upon by the necessity of generating more accurate models for hydrostatic gas films found in hybrid gas bearings. Pressurized air at room temperature up to 120 psi was used to test different recess geometries on a flat plate test rig, capable of characterizing the stiffness and damping force coefficients for varying supply pressures, gas film thickness values, excitation frequencies, and vibration amplitudes. The test rig design and operation is described. Experimental results include frequency-dependent stiffness and damping coefficients, and leakage. The test results show that using external pressurization can generate large stiffness values while exhibiting small leakage. However, the results also show that the majority of the test configurations portray high negative damping values. An analytical model is presented and numerical predictions are compared to experimental results. Example damping trends as a function of frequency, pressure, and film thickness are presented in addition to force coefficient plots as functions of pressure ratio.

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References

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Lubell, D. R. , Wade, J. L. , Chauhan, N. S. , and Nourse, J. G. , 2008, “Identification and Correction of Rotor Instability in an Oil-Free Gas Turbine,” ASME Paper No. GT2008-50305.
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Delgado, A. , 2015, “Experimental Identification of Dynamic Force Coefficients for a 110 Mm Compliantly Damped Hybrid Gas Bearing,” ASME J. Eng. Gas Turbines Power, 137(7), p. 072502. [CrossRef]
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Arghir, M. , Hassini, M. A. , Balducchi, F. , and Gauthier, R. , 2016, “Synthesis of Experimental and Theoretical Analysis of Pneumatic Hammer Instability in an Aerostatic Bearing,” ASME J. Eng. Gas Turbines Power, 138(2), p. 021602. [CrossRef]
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Figures

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Fig. 1

Flat plate test bench: (1) proximity probes measuring excitation plate vibration with respect to stationary mounting plate, (2) force transducer, (3) electrohydraulic exciter, (4) support column, (5) base, (6) excitation plate, (7) stationary mounting plate, and (8) pitch stabilizers

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Fig. 2

Flat plate geometry

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Fig. 3

Computational flow domain

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Fig. 4

Flowchart for computation of mass flow balance and force coefficients

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Fig. 5

Leakage measurements

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Fig. 6

Pressure profile across pad length

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Fig. 7

Dynamic input force

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Fig. 8

Vibration motion response of flat plate

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Fig. 9

Force coefficients for plate with 1 × 1 in2 (25.4 × 25.4 mm2), 0.016 in (0.41 mm) deep recess and 0.032 in (0.81 mm) inlet orifice diameter versus excitation frequency (ω). Three inlet pressures (40, 90, 120 psi/2.7, 6.1, 8.2 bar) and three film thickness (0.0015, 0.001, 0.00075 in/31.8, 25.4, 19.1 mm). Smooth lines: experiments, dotted lines: numerical predictions.

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Fig. 10

Force coefficients for plate with 0.65 × 0.65 in (16.5 × 16.5 mm2), 0.008 in (0.20 mm) deep recess and 0.050 (1.27 mm) inlet orifice diameter versus excitation frequency (ω). Three inlet pressures (40, 90, 120 psi/2.7, 6.1, 8.2 bar) and three film thickness (0.0015, 0.001, 0.00075 in/31.8, 25.4, 19.1 mm). Smooth lines: experiments, dotted lines: numerical predictions.

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Fig. 11

Experimental and numerical gas film stiffness and damping at 128 Hz for multiple inlet pressures and film thicknesses (1 in × 1 in (25.4 × 25.4 mm2), 0.016 in (0.41 mm) recess, 0.032 in (0.81 mm) in orifice)

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Fig. 12

Experimental and numerical gas film stiffness and damping at 128 Hz for multiple inlet pressures and film thicknesses (0.65 in × 0.65 in (16.5 × 16.5 mm2), 0.008 in (0.20 mm) recess, 0.050 in (1.27 mm) orifice)

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Fig. 13

Surface plots displaying plate A nondimensional stiffness (a) and damping (b) as a function of pressure ratio (pr) and excitation frequency (ω). Dotted lines: experiments, solid lines: numerical predictions.

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Fig. 14

Surface plots displaying plate B nondimensional stiffness (a) and damping (b) as a function of pressure ratio (pr) and excitation frequency (ω). Dotted lines: experiments, solid lines: numerical predictions.

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