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Research Papers: Gas Turbines: Structures and Dynamics

Rotordynamic Performance of Hybrid Air Foil Bearings With Regulated Hydrostatic Injection

[+] Author and Article Information
Behzad Zamanian Yazdi

Turbomachinery and Energy System Laboratory,
Department of Mechanical and
Aerospace Engineering,
The University of Texas at Arlington,
Arlington, TX 76019;
Energy Recovery,
San Leandro, CA 94577

Daejong Kim

Turbomachinery and Energy System Laboratory,
Department of Mechanical and
Aerospace Engineering,
The University of Texas at Arlington,
Arlington, TX 76019

Contributed by the Structures and Dynamics Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received July 4, 2017; final manuscript received July 15, 2017; published online September 19, 2017. Editor: David Wisler.

J. Eng. Gas Turbines Power 140(1), 012506 (Sep 19, 2017) (8 pages) Paper No: GTP-17-1278; doi: 10.1115/1.4037667 History: Received July 04, 2017; Revised July 15, 2017

Air foil bearing (AFB) technology has made substantial advancement during the past decades and found its applications in various small turbomachinery. However, rotordynamic instability, friction and drag during the start/stop, and thermal management are still challenges for further application of the technology. Hybrid air foil bearing (HAFB), utilizing hydrostatic injection of externally pressurized air into the bearing clearance, is one of the technology advancements to the conventional AFB. Previous studies on HAFBs demonstrate the enhancement in the load capacity at low speeds, reduction or elimination of the friction and wear during starts/stops, and enhanced heat dissipation capability. In this paper, the benefit of the HAFB is further explored to enhance the rotordynamic stability by employing a controlled hydrostatic injection. This paper presents the analytical and experimental evaluation of the rotordynamic performance of a rotor supported by two three-pad HAFBs with the controlled hydrostatic injection, which utilizes the injections at particular locations to control eccentricity and attitude angle. The simulations in both time domain orbit simulations and frequency-domain modal analyses indicate a substantial improvement of the rotor-bearing performance. The simulation results were verified in a high-speed test rig (maximum speed of 70,000 rpm). Experimental results agree with simulations in suppressing the subsynchronous vibrations but with a large discrepancy in the magnitude of the subsynchronous vibrations, which is a result of the limitation of the current modeling approach. However, both simulations and experiments clearly demonstrate the effectiveness of the controlled hydrostatic injection on improving the rotordynamic performance of AFB.

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References

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Figures

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Fig. 1

Rotor-bearing configuration and the coordinate system

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Fig. 2

Rotor-bearing axial coordinate configuration

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Fig. 3

Schematic of a preloaded three-pad AFB

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Fig. 4

Hydrostatic top foil with welded orifice tube

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Fig. 5

Schematic of the three-pad HAFB

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Fig. 6

Three-pad HAFB with three orifice tubes

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Fig. 7

Cross section view of the rotordynamic test rig

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Fig. 8

Simulated waterfall plots: (a) hydrodynamic mode, (b) full hybrid mode, and (c) controlled hybrid mode

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Fig. 9

Predicted synchronous peak-to-peak vibration of the rotor for in-phase imbalance

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Fig. 10

Predicted synchronous peak-to-peak vibration of the rotor for out-phase imbalance

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Fig. 11

Rotor imbalance response: (a) 35,000 rpm, (b) 40,000 rpm, and (c) 45,000 rpm (feed pressure is 4.14 bar) (adopted from Ref. [29])

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Fig. 12

Simulated rotor imbalance response: (a) 35,000 rpm, (b) 40,000 rpm, and (c) 45,000 rpm (feed pressure is 4.14 bar)

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Fig. 13

Normalized pressure profile at 20,000 rpm: (a) hydrodynamic mode, (b) full hybrid mode, and (c) controlled hybrid mode (feed pressure is 4.14 bar)

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Fig. 14

(a) Predicted rotor eccentricity and (b) attitude angle versus speed

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Fig. 15

Simulated orbits at 40,000 rpm: (a) full hybrid mode and (b) controlled hybrid mode

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Fig. 16

Modal impedances for the forward whirl versus the excitation frequency ratio for cylindrical mode at 40,000 rpm

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Fig. 17

Modal impedances for the forward whirl versus the excitation frequency ratio for conical mode at 40,000 rpm

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