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Research Papers

A Thermoelastohydrodynamic Analysis for the Static Performance of High-Speed—Heavy Load Tilting-Pad Journal Bearing Operating in the Turbulent Flow Regime and Comparisons to Test Data

[+] Author and Article Information
Hirotoshi Arihara

Kobe Steel LTD,
Kobe-city 651-2271, Hyogo, Japan
e-mail: arihara.hirotoshi@kobelco.com

Yuki Kameyama, Yoshitaka Baba

Kobe Steel LTD.,
Takasago-city 676-8670, Hyogo, Japan

Luis San Andrés

Fellow ASME
Mechanical Engineering Department,
Texas A&M University,
College Station, TX 77843

Manuscript received July 5, 2018; final manuscript received July 17, 2018; published online October 4, 2018. Editor: Jerzy T. Sawicki.

J. Eng. Gas Turbines Power 141(2), 021023 (Oct 04, 2018) (9 pages) Paper No: GTP-18-1445; doi: 10.1115/1.4041130 History: Received July 05, 2018; Revised July 17, 2018

Tilting-pad journal bearings (TPJBs) ensure rotordynamic stability that could otherwise produce dangerously large amplitude rotor oil-whirl/whip motions in high-speed rotating machinery. Currently, highly efficient turbo compressors demand an ever increasing rotor surface speed and specific load on its support bearings. The accurate prediction of bearing performance is vital to guarantee reliable products, specifically with regard to reducing maximum bearing pad temperature and drag power losses, and operating with the least flow rate while still maximizing load capacity. The hydrodynamic pressure and heat generation in an oil film acting on a bearing pad produce significant mechanical and thermal deformations that change the oil film geometry (clearance and preload) to largely affect the bearing performance, static, and dynamic. In addition, a high surface speed bearing often operates in the turbulent flow regime that produces a notable increase in power loss and a drop in maximum pad temperature. This paper details a thermoelastohydrodynamic (TEHD) analysis model applied to TPJBs, presents predictions for their steady-load performance, and discusses comparisons with experimental results to validate the model. The test bearing has four pads with a load between pads configuration; its length L = 76.2 mm and shaft diameter D = 101.6 mm (L/D = 0.75). The rotor top speed is 22.6 krpm, i.e., 120 m/s surface speed, and the maximum specific load is 2.94 MPa for an applied load of 23 kN. The test procedure records shaft speed and applied load, oil supply pressure/temperature and flow rate, and also measures the pads' temperature and shaft temperature, as well as the discharge oil (sump) temperature. The TEHD model couples a generalized Reynolds equation for the hydrodynamic pressure generation with a three-dimensional energy transport equation for the film temperature. The pad mechanical deformation due to pressure utilizes the finite elemental method, whereas an analytical model estimates thermally induced pad crowning deformations. For operation beyond the laminar flow regime, the analysis incorporates the eddy viscosity concept for fully developed turbulent flow operation. Current predictions demonstrate the influence of pressure and temperature fields on the pads mechanical and thermally induced deformation fields and also show static performance characteristics such as bearing power loss, flow rate, and pad temperatures. The comparisons of test results and analysis results reveal that turbulent flow effects significantly reduce the pads' maximum temperature while increasing the bearing power loss. Turbulent flow mixing increases the diffusion of thermal energy and makes more uniform the temperature profile across the film.

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References

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Figures

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Fig. 1

A geometry of a four pads TPJB and coordinate system

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Fig. 2

Pad finite element method structure model and constraint condition [21]

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Fig. 3

Static condensation of pad stiffness matrix: (a) original pad FE model (22,572 DOFs) and (b) reduced pad FE model (836 DOFs)

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Fig. 4

Schematic view of thermally induced deformations in a pad and journal [28]

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Fig. 5

Cross section of bearing test rig

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Fig. 6

Photograph of test rig opened to showcase test bearing and support bearings

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Fig. 7

Location of thermocouples in pads of test bearing: (a) location of thermocouples in bearing side view and (b) axial and circumferential position of thermocouples

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Fig. 8

Shaft surface temperature measurement points

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Fig. 9

Temperature distribution in bearing pads (measured and predictions) and pad deformations for test bearing. Journal surface speed =120 m/s, specific load =2.94 MPa: (a) measured and predicted temperatures in pads and (b) thermally induced and pressure elastic deformation of the pads.

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Fig. 10

Predicted max. Reynolds number versus journal surface speed (specific load =2.94 MPa).

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Fig. 11

Predicted temperatures at midplane of loaded pad (#4) for operation with journal surface speed =120 m/s, specific load =2.94 MPa: (a) laminar flow model, (b) turbulent flow model, and (c) temperature distribution across film of pad#4 trailing edge

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Fig. 12

Measured and predictions for bearing static performance versus surface speed (specific load =2.94 MPa): (a) maximum pad#4 temperature (85%), (b) journal surface temperature, (c) bearing drag power loss, and (d) bearing oil flow rate

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