Research Papers: Gas Turbines: Structures and Dynamics

Extended Three-Dimensional Thermo-Hydrodynamic Model of Radial Foil Bearing: Case Studies on Thermal Behaviors and Dynamic Characteristics in Gas Turbine Simulator

[+] Author and Article Information
Daejong Kim1

 Mechanical and Aerospace Engineering Department, University of Texas at Arlington, 500 W. 1st Street, Arlington, TX 76019daejongkim@uta.edu

Jeongpill Ki

 Mechanical and Aerospace Engineering Department, University of Texas at Arlington, 500 W. 1st Street, Arlington, TX 76019

Youngcheol Kim, Kookyoung Ahn

 Korea Institute of Machinery and Materials, 171 Jang-dong, Yuseong-Gu, Daejeon, S. Korea 305-343


Corresponding author.

J. Eng. Gas Turbines Power 134(5), 052501 (Feb 15, 2012) (13 pages) doi:10.1115/1.4005215 History: Received April 13, 2011; Revised September 09, 2011; Published February 15, 2012; Online February 15, 2012

Environment-friendly microturbomachinery has its broad current and future applications in fuel cells, power generation, oil-free industrial blowers and compressors, small aero propulsions engines for missiles and small aircrafts, automotive turbo chargers, etc. Air foil bearings (AFBs) have been one of the popular subjects in recent years due to ever-growing interests in the environment-friendly oil-free turbomachinery. AFBs have many noticeable attractive features compared to conventional rigid-walled air/gas bearings such as improved damping and tolerance to minor shaft misalignment and external shocks. In addition, the low viscosity of air or gas allows very low power consumption even at high speeds. A turbine simulator mimicking 50 kW power generation gas turbine was designed. The turbine simulator can generate the same thermodynamic conditions and axial thrust load as the actual gas turbine. In this paper, the 3-D thermo-hydrodynamic (THD) model developed for single radial AFB was further extended to the turbine simulator configuration by extending the solution domain to the surrounding structures including two plenums, bearing sleeve, housing, and rotor exposed to the plenums. In addition, a computational fluid dynamic (CFD) model on the leading edge groove region was developed for better prediction of inlet thermal boundary conditions for the bearing. Several case studies are presented through computer simulations for hydrodynamically preloaded three-pad radial AFB in the hot section. It is found that both bearing and rotor should be provided with cooling air to maintain the temperature of both the rotor and top foil below 300 °C. It is also found that the higher thermal contact resistance between the rotor and hot impellers reduces the axial temperature gradient of the rotor. Dynamic performance of the bearing was evaluated using the linear perturbation method for operation at elevated temperature. The softening effect of the bump foil at elevated temperature results in a decrease of both stiffness and damping coefficients compared to the values at room temperature.

Copyright © 2012 by American Society of Mechanical Engineers
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Figure 1

Definition of preload, set bore clearance, and pad configuration

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Figure 2

Photo of designed turbine simulator; instrumentations are not shown

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Figure 3

Cross section of the turbine simulator; P1  ∼ P5 are the plenum locations and C1  ∼ C5 are locations of the cooling air inlets or discharges. Pt and Tt denote the pressure and temperature at hot section (turbine) and Pc and Tc denote the pressure and temperature at cold section (compressor).

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Figure 4

Simplified thermal domains of the surrounding structures around the radial foil bearing close to turbine and thermal boundary conditions. Two main cooling air flows are shown with dotted arrows (leakage flows from the bearing to the plenums are not shown).

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Figure 5

Dimensions of surrounding structures; other dimensions are in Tables  34

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Figure 6

Details of cooling channels on the rotor. (a) Leading edge region. (b) Cross section of simplified model of the leading edge region.

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Figure 7

Model of the leading edge region. (a) Isometric view of the mesh. (b) Side view of the mesh.

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Figure 8

CFD meshes of the leading edge groove region

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Figure 9

Cross-film temperature distributions at leading edge plane for axial cooling case, rotor reference speed 50,000 rpm

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Figure 10

λ map for the axial cooling cases from the CFD model. (a) Cooling through only bump channels. (b) Cooling through both bump and rotor channels.

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Figure 11

Cross-film averaged temperature distribution, 4000 Pa axial cooling, 50,000 rpm

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Figure 12

Rotor temperature distributions for axial cooling cases, 50,000 rpm, 4000 Pa; the region between the two lines at center is inside the bearing. (a) Cooling through only bump channels. (b) Cooling through both bump and rotor channels.

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Figure 13

Top foil temperature, 4000 Pa axial cooling, 50,000 rpm. (a) Cooling through only bump channels. (b) Cooling through both bump and rotor channels.

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Figure 14

Rotor temperature distributions for different axial cooling pressures with increased thermal insulation from hot section, 50,000 rpm; temperatures in the parenthesis are the average top foil temperature. (a) Stiffness coefficients. (b) Damping coefficients.

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Figure 15

Stiffness and damping coefficients of the bearing at 50,000 rpm; black: isothermal at 20°C; red: from THD solution. Coordinate system follows Fig. 1.



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