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Gas Turbines: Structures and Dynamics

On The Nonlinear Dynamics of Two Types of Backup Bearings — Theoretical and Experimental Aspects

[+] Author and Article Information
Said Lahriri1

 Department of Solid Mechanical, Technical University of Denmark, Nils Koppels Allé, Bygning 404, DK-2800 Kgs. Lyngby, Denmark, e-mail: slah@mek.dtu.dk Lloyd’s Register ODS, Strandvejen 104A, 1, DK-2900 Hellerup, Denmark e-mail: said.lahriri@lr-ods.com

Ilmar F. Santos

 Department of Solid Mechanical, Technical University of Denmark, Nils Koppels Allé, Bygning 404, DK-2800 Kgs. Lyngby, Denmark e-mail: ifs@mek.dtu.dk

Hans I. Weber

 Department of Mechanical Engineering, Pontifícia Universidade Católica, PUC-Rio de Janeiro, Rua Marquês de São Vicente, 225- Gávea-22453-900 Rio de Janeiro, Brazil e-mail: hans@puc-rio.br

Henning Hartmann

Lloyd’s Register ODS, Strandvejen 104A, 1, DK-2900 Hellerup, Denmark e-mail: Henning.Hartmann@lr-ods.com

1

Corresponding author.

J. Eng. Gas Turbines Power 134(11), 112503 (Sep 28, 2012) (13 pages) doi:10.1115/1.4007166 History: Received June 22, 2012; Revised July 06, 2012; Published September 28, 2012; Online September 28, 2012

The possible contact between rotor and stator can for some cases be considered a serious malfunction that may lead to catastrophic failure. Rotor rub is considered a secondary phenomenon caused by a primary source that leads to a disruption of the normal operational condition. It arises from sudden mass unbalance, instabilities generated by aerodynamic and hydrodynamic forces in seals and bearings among others. The contact event gives rise to normal and friction forces exerted on the rotor at impact events. The friction force plays a significant role by transferring some rotational energy of the rotor to lateral motion, impacting the stator. This event results in persistent coupled lateral vibration of the rotor and stator. This paper proposes a new unconventional backup bearing design in order to reduce the rub related severity in friction. The idea is to utilize pin connections that center the rotor during impacts. In this way, the rotor is forced to the center and the lateral motion is mitigated. The four pins are passively adjustable, which allows the clearance to be customized. A mathematical model has been developed to capture phenomena arising from impact for the conventional backup bearing (annular guide) and for the new disk-pin backup bearing. For the conventional annular guide setup, it is reasonable to superpose an impact condition to the rub, where the rotor spin energy can be fully transformed into rotor lateral movements. Using a nonideal drive, i.e., an electric motor without any kind of velocity feedback control, it is even possible to almost stop the rotor spin under rubbing conditions. All the rotational energy will be transformed in a kind of “self-excited” rotor lateral vibration with repeated impacts against the housing. The vibration of the housing is coupled through the interaction force. The experimental and numerical analysis shows that for the conventional annular guide setup, the rotational energy is fully transformed into lateral motion and the rotor spin is stopped. However, by employing the new disk-pin design the analysis shows that the rotor at impact is forced to the center of the backup bearing and the lateral motion is mitigated. As a result of this, the rotor spin is kept constant.

Copyright © 2012 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

(a) Picture of the annular guide, experimental setup, (b) mechanical model of the annular guide, (c) picture of the new unconventional disk-pin contact design, experimental setup, and (d) mechanical model of the new unconventional disk-pin contact design

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Figure 2

(a) Test setup picture, (b) new backup bearing design, and (c) attached disk within the new backup bearing design

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Figure 3

(a) First and second bending modes, (b) hanging shaft with attached disk, and (c) rotations of the disk

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Figure 4

(a) Deflected shape in the inertial (X,Z) plane and (b) deflected shape in the inertial (Y,Z) plane

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Figure 5

Subsystem, impact motion, and forces

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Figure 6

Modified Coulomb friction model

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Figure 7

Subsystem, impact motion, and forces for the new backup bearing design

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Figure 8

(a) Characteristic torque curve of the ac motor, obtained experimentally, and (b) characteristic torque curves obtained for different values of C [23]

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Figure 9

Experiment: (a) time series y motion, (b) time series z motion, (c) trajectories of the center of the disk within the bearing clearance, and (d) angular velocity of the disk Rd/r0 = 100

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Figure 10

Experiment: (a) velocity of the disk in the y direction and (b) velocity of the disk in the z direction

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Figure 11

Experiment: Contour half-spectrum FFT plot Rd/r0 = 100

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Figure 12

Experiment: Waterfall full-spectrum FFT plot Rd/r0 = 100

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Figure 13

Experiment: (a) full-spectrum plot and (b) filtered orbit plot Rd/r0 = 100

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Figure 14

Numerical, torsional stiffness not included: (a) time series y motion, (b) time series z motion, (c) trajectories of the center of the disk within the bearing clearance, and (d) angular velocity of the disk Rd/r0 = 100

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Figure 15

Numerical: (a) time series y motion, (b) time series z motion, (c) trajectories of the center of the disk within the bearing clearance, and (d) angular velocity of the disk Rd/r0=100

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Figure 16

(a) Experiment: Displacement of the disk in the y direction. (b) Numerical: Displacement of the disk in the y direction.

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Figure 17

Experiment: (a) time series y motion, (b) time series z motion, (c) trajectories of the center of the disk within the bearing clearance, and (d) angular velocity of the disk Rd/r0 = 833

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Figure 18

Experiment: Contour half-spectrum FFT plot Rd/r0 = 833

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Figure 19

Experiment: Waterfall full-spectrum FFT plot Rd/r0 = 833

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Figure 20

Experiment: (a) full-spectrum plot and (b) filtered orbit plot Rd/r0 = 833

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Figure 21

Numerical: (a) time series y motion, (b) time series z motion, (c) trajectories of the center of the disk within the bearing clearance, and (d) angular velocity of the disk Rd/r0 = 833

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