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Research Papers: Gas Turbines: Structures and Dynamics

Stability Analysis of an Industrial Gas Compressor Supported by Tilting-Pad Bearings Under Different Lubrication Regimes

[+] Author and Article Information
Alejandro Cerda Varela1

Department of Mechanical Engineering,  Technical University of Denmark, 2800 Kgs. Lyngby, Denmarkacer@mek.dtu.dk

Ilmar Ferreira Santos

Department of Mechanical Engineering,  Technical University of Denmark, 2800 Kgs. Lyngby, Denmarkifs@mek.dtu.dk

1

Corresponding author.

J. Eng. Gas Turbines Power 134(2), 022504 (Dec 20, 2011) (11 pages) doi:10.1115/1.4004214 History: Received April 27, 2011; Revised May 03, 2011; Published December 20, 2011; Online December 20, 2011

This work is aimed at a theoretical study of the dynamic behavior of a rotor-tilting pad journal bearing (TPJB) system under different lubrication regimes, namely, thermohydrodynamic (THD), elastohydrodynamic (EHD), and hybrid lubrication regime. The rotor modeled corresponds to an industrial compressor. Special emphasis is put on analyzing the stability map of the rotor when the different lubrication regimes are included into the TPJB modeling. Results show that, for the studied rotor, the inclusion of a THD model is more relevant when compared to an EHD model, as it implies a reduction on the instability onset speed for the rotor. Also, results show the feasibility of extending the stable operating range of the rotor by implementing a hybrid lubrication regime.

Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

Mechanical model of the compressor by shaft elements; global coordinate system (x,y,z) and pad local coordinate system (x¯,y¯,z¯) used for the study

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Figure 2

Static equilibrium position for bearing 1, as a function of the rotational speed; results for the eccentricity ratio of the rotor journal and the rotation of pad #4

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Figure 3

Oil film thickness for bearing 1 pad #4 at equilibrium position; comparison of results for 6000 RPM (left) and 11,000 RPM (right). Results obtained at Z¯=0.

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Figure 4

Pressure profile at equilibrium position for bearing 1 pad #4; comparison of results for 6000 RPM (left) and 11,000 RPM (right). Result obtained at Z¯=0.

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Figure 6

Synchronously reduced direct stiffness and damping coefficients for bearing 1, vertical direction: comparison between rigid pads and flexible pads with different numbers of flexible modes included

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Figure 7

Stability map for the compressor; comparison between rigid pads and flexible pads model, for different numbers of modes (figure to the right details the instability onset zone)

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Figure 8

Oil film temperature for bearing 1 pad #4 at equilibrium position; comparison of results for 6000 RPM (left) and 11,000 RPM (right)

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Figure 9

Static equilibrium position for bearing 1, as a function of rotational speed; results for eccentricity ratio of the rotor journal and the rotation of pad #4

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Figure 10

Synchronously reduced direct stiffness and damping coefficients for bearing 1, vertical direction; effect of including THD model

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Figure 11

Stability map for the compressor; effect of including the THD model for the oil film (figure to the right details the instability onset zone)

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Figure 12

Stability map for the compressor, calculated using the TPJBs synchronously reduced dynamic coefficients for different lubrication regimes

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Figure 13

Static equilibrium for bearing 1, as a function of rotational speed; results for the eccentricity ratio of the rotor journal and the rotation of pad #4, effect of oil injection for two configurations

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Figure 14

Synchronously reduced direct stiffness and damping coefficients for bearing 1, vertical direction; effect of oil injection for two configurations

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Figure 15

Stability map for the compressor; effect of hybrid oil injection for two configurations (figure to the right details the instability onset zone)

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Figure 16

Stability map for the compressor; effect of injection pressure for hybrid regime with “two holes” configuration (figure to the right details the instability onset zone)

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Figure 5

Deformation of bearing 1 pad #4 at equilibrium position; comparison of results for 6000 RPM (left) and 11,000 RPM (right)

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