Research Papers: Hydrodynamic Lubrication

Real-Gas Effects in Foil Thrust Bearings Operating in the Turbulent Regime

[+] Author and Article Information
T. M. Conboy

Member ASME
Advanced Nuclear Concepts,
Sandia National Laboratories,
P.O. Box 5800, MS 1136,
Albuquerque, NM 87185
e-mail: tmconbo@sandia. gov

Contributed by the Tribology Division of ASME for publication in the Journal of Tribology. Manuscript received July 23, 2012; final manuscript received March 4, 2013; published online May 10, 2013. Assoc. Editor: Luis San Andres.

J. Tribol 135(3), 031703 (Mar 04, 2013) (12 pages) Paper No: TRIB-12-1119; doi: 10.1115/1.4024048 History: Received July 23, 2012; Revised March 04, 2013

In this study, an elastohydrodynamic model was created for predicting the pressure field in a compliant thrust bearing assembly lubricated by high pressure CO2. This application is of significance due to ongoing research into the closed-cycle supercritical CO2 turbine as a high-efficiency alternative to steam turbines. Hardware development for this concept has been led by Sandia National Laboratories, where turbomachinery running on gas foil thrust and journal bearings is being tested. The model accounts for the fluid velocity field, hydrodynamic pressure, and frictional losses within the lubrication layer by evaluating the turbulent Reynolds equation coupled with an equation for structural deformation in the bearings, and the fluid properties database RefProp v9.0. The results of numerical simulations have been compared with empirical correlations, with reasonable agreement attained. Of particular interest is the contrast drawn between the performance of high pressure CO2 as a lubricant, and ambient pressure air. Parametric studies covering a range of fluid conditions, operating speeds, and thrust loads were carried out to illustrate the value of this model as a tool for improved understanding and further development of this nascent technology.

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Fig. 1

Schematic of the S-CO2 turbo-alternator-compressor [3]

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Fig. 2

Schematic of a compliant foil thrust bearing [18]

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Fig. 3

Nomenclature used to describe the lubrication film relative to the bearing structure [18]

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Fig. 4

Values of linearized turbulence coefficients due to Hirs

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Fig. 5

Nomenclature used to define the thrust bearing surface geometry [18]

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Fig. 6

Block diagram of the bearings model solver

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Fig. 7

Prototype thrust bearing with one top foil removed [27]

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Fig. 8

Profile of the thrust bearings compliance coefficient α in atmospheric air

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Fig. 9

Multipad simulation results for the pressure profile of a heavily loaded in CO2 at 1.4 MPa, 75,000 rpm

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Fig. 10

Single-pad simulation results for relative displacement of a heavily loaded bearing in CO2 at 1.4 MPa, 75,000 rpm

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Fig. 11

Variation of load capacity with runner speed

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Fig. 12

Variation of load capacity with bearings diameter

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Fig. 13

Variation of power loss with runner speed, CO2 and air

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Fig. 14

Variation of stiffness with runner speed, CO2 and air

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Fig. 15

Variation of power loss with CO2 film pressure

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Fig. 16

Variation of power loss with CO2 film temperature

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Fig. 17

Variation of power loss with bearings diameter, for o.d./i.d. = 2

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Fig. 18

Variation of film thickness and power loss with increasing thrust load

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Fig. 19

Variation of load capacity with runner speed and CO2 film density




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