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Research Papers: Gas Turbines: Oil and Gas Applications

Static Load Performance of a Water-Lubricated Hydrostatic Thrust Bearing

[+] Author and Article Information
Michael Rohmer

Machinery Engineer,
ExxonMobil Research & Engineering,
Spring, TX 77389
e-mail: michael.a.rohmer@exxonmobil.com

Luis San Andrés

Fellow ASME
Mechanical Engineering Department,
Texas A&M University,
College Station, TX 77843
e-mail: lsanandres@tamu.edu

Scott Wilkinson

Mechanical Engineering Department,
Texas A&M University,
College Station, TX 77843
e-mail: wilk1847@tamu.edu

Contributed by the Oil and Gas Applications Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received July 31, 2017; final manuscript received September 11, 2017; published online February 27, 2018. Editor: David Wisler.

J. Eng. Gas Turbines Power 140(6), 062401 (Feb 27, 2018) (10 pages) Paper No: GTP-17-1419; doi: 10.1115/1.4038472 History: Received July 31, 2017; Revised September 11, 2017

In rotating equipment, thrust bearings aid to balance axial loads and control shaft position. In turbomachinery, axial loads depend on shaft speed and pressure rise/drop on the impellers. This paper details a water-lubricated test rig for measurement of the performance of hydrostatic thrust bearings (HTBs). The rig contains two water-lubricated HTBs (105 mm outer diameter (OD)), one is the test bearing and the other a slave bearing. Both bearings face the outer side of thrust collars of a rotor. The paper shows measurements of HTB axial clearance, flow rate, and recess pressure for operation with increasing static load (max. 1.4 bar) and supply pressure (max. 4.14 bar) at a rotor speed of 3 krpm (12 m/s OD speed). Severe angular misalignment, static and dynamic, of the bearing surface against its collar persisted and affected all measurements. The HTB axial clearance increases as the supply pressure increases and decreases quickly as the applied load increases. The reduction in clearance increases the flow resistance across the film lands, thus reducing the through flow rate with an increase in recess pressure. In addition, an estimated bearing axial stiffness increases as the operating clearance decreases and as the supply pressure increases. Predictions from a bulk flow model qualitatively agree with the measurements. Alas they are not accurate enough. The differences likely stem from the inordinate tilts (static and dynamic) as well as the flow condition. The test HTB operates in a flow regime that spans from laminar to incipient turbulent. Quantification of misalignment at all operating conditions is presently a routine practice during operation of the test rig.

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References

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Figures

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Fig. 1

Cross-sectional view of thrust bearing test rig [17]

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Fig. 2

Photograph of thrust bearing test rig with the top half of housing removed [17]

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Fig. 3

Schematic view of flexure pivot, tilting pad hydrostatic bearing. Orifices for liquid injection shown.

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Fig. 4

Depiction of water-lubricated test HTB. Orifice diameter = 1.55 mm. Location of eddy current sensors noted.

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Fig. 5

Depiction of axial clearance Co and tilt angles (δx, δy) between thrust collar and bearing surface

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Fig. 6

Test and slave HTBs: measured axial clearance (C0) versus specific load (W/A). Operation with water (24 °C) at (PS) = 2.76, 3.45, and 4.14 bar(g) into the thrust bearings. No shaft rotation. (a) test thrust bearing and (b) slave thrust bearing.

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Fig. 7

Test HTB: recess pressure ratio (PR/PS) versus axial clearance (C0) and versus specific load (W/A). Operation with water (24 °C) at (PS)=2.76, 3.45, and 4.14 bar(g). No shaft rotation: (a) recess pressure ratio versus axial clearance and (b) recess pressure ratio versus specific axial load.

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Fig. 8

Thrust collar misalignments: (top) static (δx, δy) versus clearance (Co); (bottom) example of dynamic (δx, δy) versus frequency. Shaft speed = 3 krpm (50 Hz) and water at PS = 3.45 bar(g).

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Fig. 9

Test and slave HTBs: Experimental axial clearance (C0) versus specific load (W/A) for Operation with water (31 °C) at PS = 2.76, 3.45, and 4.14 bar(g). Shaft rotates at 3 krpm. (a) test thrust bearing and (b) slave thrust bearing.

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Fig. 10

Test and slave HTBs: Experimental axial clearance (C0) versus specific load (W/A). Tests without and with rotor speed (3 krpm). Water (24 °C, 31 °C) at PS = 2.76, 3.45, and 4.14 bar(g): (a) PS = 2.76 bar(g), (b) PS = 3.45 bar(g), and (c) PS = 4.14 bar(g).

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Fig. 11

Test HTB: Supply flow rate versus axial clearance (C0) for operation with water (31 °C) at PS = 2.76, 3.45, and 4.14 bar(g). Shaft rotates at 3 krpm.

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Fig. 12

Test HTB: Flow rate through ID versus axial clearance (C0). Water (31 °C) at PS = 2.76, 3.45, and 4.14 bar(g). Shaft rotates at 3 krpm.

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Fig. 13

Test HTB: Ratio of exhaust flow through bearing ID to supply flow versus (top) axial clearance (C0) and (bottom) specific load. Water (31 °C) at supply pressure PS = 2.76, 3.45, and 4.14 bar(g). Shaft rotates at 3 krpm: (a) ID flow/supply flow versus axial clearance (C0) and (b) ID flow/supply flow versus load/area.

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Fig. 14

Test HTB: Recess pressure ratio (PR/PS) versus axial clearance (C0). Water (31 °C) at supply pressure (PS) = 2.76, 3.45, and 4.14 bar(g). Shaft rotates at 3 krpm.

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Fig. 20

Test HTB: Static axial stiffness estimated from test data and predicted (lines) versus axial clearance (C0). Water (31 °C) at PS = 2.76, 3.45, and 4.14 bar(g). Shaft rotates at 3krpm.

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Fig. 19

Measured and predicted recess pressure ratio (PR/PS) versus specific axial load (W/A). Water (31 °C) at PS = 2.76, 3.45, and 4.14 bar(g). Shaft rotates at 3 krpm.

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Fig. 18

Measured and predicted flow rate through HTB ID versus specific axial load. Operation with water (31 °C) at PS = 2.75, 3.45, and 4.14 bar(g). Shaft rotates at 3 krpm.

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Fig. 17

Measured and predicted supply flow rate to test HTB versus specific axial load (W/A). Water (31 °C) at PS = 2.76, 3.45, and 4.14 bar(g). Shaft rotates at 3 krpm.

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Fig. 16

Measured and predicted axial clearance (C0) versus specific load (W/A). (Left) test HTB and (right) slave HTB. Water at PS = 2.76, 3.45, and 4.14 bar(g). Shaft rotates at (top) 0krpm and (bottom) 3 krpm.

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Fig. 15

Test HTB: empirical orifice discharge coefficient (Cd) versus axial clearance (C0). Water (31 °C) at PS = 2.76, 3.45, and 4.14 bar(g). Shaft rotates at 3 krpm.

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