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Research Papers: Gas Turbines: Structures and Dynamics

Nonlinear Analysis of Rub Impact in a Three-Disk Rotor and Correction Via Bearing and Lubricant Adjustment

[+] Author and Article Information
Brian K. Weaver

Rotating Machinery and Controls Laboratory,
Department of Mechanical and
Aerospace Engineering,
University of Virginia,
122 Engineer’s Way,
Charlottesville, VA 22904
e-mail: bkw3q@virginia.edu

Ya Zhang

College of Mechanical and
Electrical Engineering,
Beijing University of Chemical Technology,
P.O. Box 93, No. 15 Beisanhuan East Road,
Chaoyang District,
Beijing 100029, China
e-mail: zhangya@mail.buct.edu.cn

Andres F. Clarens

Rotating Machinery and Controls Laboratory,
Department of Civil and
Environmental Engineering,
University of Virginia,
351 McCormick Road,
Charlottesville, VA 22904
e-mail: aclarens@virginia.edu

Alexandrina Untaroiu

Rotating Machinery and Controls Laboratory,
Department of Mechanical and
Aerospace Engineering,
University of Virginia,
122 Engineer’s Way,
Charlottesville, VA 22904
e-mail: au6d@virginia.edu

Contributed by the Structures and Dynamics Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received December 2, 2014; final manuscript received January 30, 2015; published online February 25, 2015. Editor: David Wisler.

J. Eng. Gas Turbines Power 137(9), 092504 (Sep 01, 2015) (8 pages) Paper No: GTP-14-1644; doi: 10.1115/1.4029778 History: Received December 02, 2014; Revised January 30, 2015; Online February 25, 2015

Rubbing between rotating and stationary surfaces in turbomachinery can result in catastrophic failures if not caught quickly. Removing the rub impact can then often require time consuming and expensive solutions including field balancing or magnetic bearing systems. However, simple changes in bearing dynamics via bearing and lubricant adjustment could provide for a faster and cheaper alternative. In this work, a three-disk rotor was examined analytically for nonlinear rotordynamic behavior due to an unbalance-driven rub. The rotordynamic solution was obtained using nonlinear and steady state finite element models to demonstrate the effect of the rub impact on the dynamic response of the machine. A thermoelastohydrodynamic (TEHD) model of tilting pad journal bearing performance was also used to study the possible removal of the rub impact by making minor adjustments to bearing parameters including preload, clearance, pad orientation, and lubricant properties. Gas-expanded lubricants (GELs), tunable mixtures of synthetic oil and carbon dioxide that have been proposed as a means to provide control in bearing-rotor systems, were also considered for their possible role in controlling the rub. The TEHD model provided a range of bearing inputs to the rotor models in the form of stiffness and damping coefficients. Results from the rotordynamic analyses included an assessment of critical speeds, peak rotor displacements, and vibration characteristics. Individual bearing parameter adjustments were found to have smaller, though still significant effects on the response of the machine. Overall, it was found that by adjusting a combination of these bearing parameters, the peak displacement of the rotor could be reduced by large enough amounts to remove the rub impact in the machine, hence providing a simple approach to solving rub impact problems in rotating machinery caused by excessive vibration.

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References

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Figures

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Fig. 1

Finite element model of the three-disk rotor

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Fig. 2

Critical speed map of the three-disk rotor, showing both forward (black lines) and backward (gray lines) modes

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Fig. 3

Center disk displacements for the 0.2 preload and LBP bearing configurations

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Fig. 4

Dynamic stiffness (a) and damping (b) coefficients for cases 2, 6, 10, and 14

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Fig. 5

Bifurcation diagrams for cases 2 (a) and 14 (b)

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Fig. 6

Shaft whirl orbits for cases 2 (a) and 14 (b)

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Fig. 7

Spectrum analysis of cases 2 (a) and 14 (b)

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Fig. 8

Center disk displacements for the 0.2 preload and LOP bearing configurations

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Fig. 9

Dynamic stiffness (a) and damping (b) coefficients for cases 1, 5, 9, and 13

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Fig. 10

Center disk displacements for the POE lubricant and 50.8 μm bearing clearance

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Fig. 11

Dynamic stiffness (a) and damping (b) coefficients for cases 1, 2, 3, and 4

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Fig. 12

Center disk displacements for the POE lubricant and 25.4 μm bearing clearance

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Fig. 13

Dynamic stiffness (a) and damping (b) coefficients for cases 5, 6, 7, and 8

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Fig. 14

Center disk displacements for the GEL lubricant cases

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Fig. 15

Dynamic stiffness (a) and damping (b) coefficients for cases 9, 10, 13, 14, 15, and 16

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