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Research Papers: Gas Turbines: Structures and Dynamics

A Water-Lubricated Hybrid Thrust Bearing: Measurements and Predictions of Static Load Performance

[+] Author and Article Information
Luis San Andrés

Mast-Childs Chair Professor,
Fellow ASME
Turbomachinery Laboratory,
Mechanical Engineering Department,
Texas A&M University,
College Station, TX 77843-3123
e-mail: lsanandres@tamu.edu

Stephen Phillips

Research Engineer
Turbomachinery Laboratory,
Mechanical Engineering Department,
Texas A&M University,
College Station, TX 77843-3123

Dara Childs

L.T. Jordan Chair Professor
Fellow ASME
Turbomachinery Laboratory,
Mechanical Engineering Department,
Texas A&M University,
College Station, TX 77843-3123

Contributed by the Structures and Dynamics Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received June 23, 2016; final manuscript received June 28, 2016; published online September 13, 2016. Editor: David Wisler.

J. Eng. Gas Turbines Power 139(2), 022506 (Sep 13, 2016) (10 pages) Paper No: GTP-16-1272; doi: 10.1115/1.4034042 History: Received June 23, 2016; Revised June 28, 2016

Process fluid-lubricated thrust bearings (TBs) in a turbomachine control rotor placement due to axial loads arising from pressure fields on the front shroud and back surface of impellers. To date, prediction of aerodynamic-induced thrust loads is still largely empirical. Thus, needs persist to design and operate proven TBs and to validate predictions of performance derived from often too restrictive computational tools. This paper describes a test rig for measurement of the load performance of water-lubricated hydrostatic/hydrodynamic TBs operating under conditions typical of cryogenic turbo pumps (TPs). The test rig comprises of a rigid rotor composed of a thick shaft and two end collars. A pair of flexure-pivot hydrostatic journal bearings (38 mm in diameter) supports the rotor and quill shaft connected to a drive motor. The test rig hosts two TBs (eight pockets with inner diameter equal to 41 mm and outer diameter equal to 76 mm); one is a test bearing and the other is a slave bearing, both facing the outer side of the thrust collars on the rotor. The slave TB is affixed rigidly to a bearing support. A load system delivers an axial load to the test TB through a nonrotating shaft floating on two aerostatic radial bearings. The test TB displaces to impose a load on the rotor thrust collar, and the slave TB reacts to the applied axial load. The paper presents measurements of the TB operating axial clearance, flow rate, and pocket pressure for conditions of increasing static load (max. 3600 N) and shaft speed to 17.5 krpm (tip speed 69.8 m/s) and for an increasing water supply pressure into the TBs, max. 17.2 bar (250 psig). Predictions from a bulk flow model that accounts for both fluid inertia and turbulence flow effects agree well with recorded bearing flow rates (supply and exiting through the inner diameter), pocket pressure, and ensuing film clearance due to the imposed external load. The measurements and predictions show a film clearance decreasing exponentially as the applied load increases. The bearing flow rate also decreases, and at the highest rotor speed and lowest supply pressure, the bearing is starved of lubricant on its inner diameter side, as predicted. The measured bearing flow rate and pocket pressure aid to the empirical estimation of the orifice discharge coefficient for use in the predictive tool. The test data and validation of a predictive tool give confidence to the integration of fluid film TBs in cryogenic TPs as well as in other more conventional (commercial) machinery. The USAF Upper Stage Engine Technology (USET) program funded the work during the first decade of the 21st century.

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References

Figures

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Fig. 1

Cross-sectional view of hydrostatic TB test rig (units: inch)

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Fig. 2

Photograph of hydrostatic TB test rig during assembly and exploded view of its components (units: inch)

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Fig. 7

Measured axial clearance of test TB versus applied load. No shaft rotation. Water at 93 °F (34 °C) and supply pressure at 3.42, 10.34 and 17.2 bar. Predictions for same range of applied load.

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Fig. 6

Cross-section view of test TB, axial load shaft, and aerostatic bearings support (units: inch)

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Fig. 5

Views of thrust hybrid bearings (test and slave): (a) test TB with piping for water outlet through OD; (b) split slave TB installed in housing

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Fig. 4

Depiction of radial hydrostatic bearing—flexure pivot type (units: inch)

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Fig. 3

Schematic representation of test rig: thrust and radial bearings as mechanical elements with stiffness and damping coefficients: axial and lateral

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Fig. 8

Measured inlet and ID discharge flow rates in test TB versus applied axial load. No shaft rotation. Water at 93 °F (34 °C) and supply pressure of 17.2 bar (250 psig). Predictions (lines) for same range of applied load.

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Fig. 9

Measured axial clearance of test TB versus applied load. Water at 93 °F (34 °C) and supply pressure at 17.2 bar (250psig). Tests with shaft rotation: 7.5, 12.5, and 17.5 krpm. Predictions (lines) for identical test conditions.

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Fig. 10

Measured axial clearance of test TB versus applied load. Water at 93 °F (34 °C) and supply pressure at 3.45 bar (50psig). Tests with shaft rotation: 7.5, 12.5, and 17.5 krpm. Predictions (lines) for identical test conditions.

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Fig. 16

Comparison of measured axial clearance on test and slave TBs versus applied load. Water at 93 °F (34 °C), supply pressure at 3.45 bar (50 psig) and shaft rotation at 17.5 krpm. Predictions (line) for identical test conditions.

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Fig. A1

Measured axial clearance at three circumferential positions (for locations, see inset) and estimated clearance at center of TB versus applied axial load. No shaft rotation. Water at 44 °C and supply pressure of 17.2 bar (250 psig). Predictions based on analysis in Ref. [10].

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Fig. 11

Measured inlet and ID discharge flow rates in test TB versus applied axial load. Water at 34 °C, supply pressure 17.2 bar (250 psig) and 7.5 krpm shaft speed. Predictions (lines) for identical test conditions.

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Fig. 12

Measured inlet and ID discharge flow rates in TB versus applied axial load. Water at 34 °C, supply pressure of 3.45 bar (50 psig) and 17.5 krpm shaft speed. Predictions (lines) for identical test conditions.

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Fig. 13

Experimentally derived recess pressure ratio (PR − Pa)/(PS − Pa) versus applied axial load. Tests with shaft rotation: 7.5, 12.5, and 17.5 krpm. Water at 34 °C (93 F) and supply pressure at 1.72 MPa (250 psig). Predictions (lines) for identical test conditions.

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Fig. 14

Estimated orifice discharge coefficient (Cd) versus TB axial clearance for tests with shaft rotation: 7.5, 12.5, and 17.5krpm. Water at 93 F (34 °C) and supply pressure at 17.2 bar (250 psig).

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Fig. 15

Estimated and predicted static stiffness (Kz) of test TB versus axial clearance for tests with shaft rotation: 7.5, 12.5, and 17.5 krpm. Water at 93 F (34 °C) and supply pressure at 17.2 bar (250 psig). Static load range: 600–1600 N.

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Fig. A2

Depiction of tilted thrust collar with respect to TB surface and locations of axial clearance measurement

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Fig. A3

Example of misalignment or tilt displacements R(δX, δY) of test TB versus applied load. Water at 93 °F (34 °C) and supply pressure at 17.2 bar (250 psig). Tests with shaft rotation at 17.5 krpm.

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