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Research Papers

Rotordynamic Force Prediction of a Shrouded Centrifugal Pump Impeller—Part II: Stability Analysis

[+] Author and Article Information
Eunseok Kim

Mem. ASME
Department of Mechanical Engineering,
Texas A&M University,
College Station, TX 77840
e-mail: euns670@tamu.edu

Alan Palazzolo

Fellow ASME
Department of Mechanical Engineering,
Texas A&M University,
College Station, TX 77840
e-mail: a-palazzolo@tamu.edu

Contributed by the Technical Committee on Vibration and Sound of ASME for publication in the JOURNAL OF VIBRATION AND ACOUSTICS. Manuscript received June 18, 2015; final manuscript received January 18, 2016; published online April 18, 2016. Assoc. Editor: John Yu.

J. Vib. Acoust 138(3), 031015 (Apr 18, 2016) (13 pages) Paper No: VIB-15-1222; doi: 10.1115/1.4032723 History: Received June 18, 2015; Revised January 18, 2016

In Paper I, some test cases of centrifugal pump impellers which showed unconventional impedances curves were reviewed and possible sources of the bump and dip in the impedance curves were investigated by simulating a wear-ring seal pump impeller. In this paper, the unconventional impedances determined in Paper I are converted into a form for inclusion in rotordynamic stability and forced response analyses. First of all, a finite element (FE) rotor model is considered to investigate the influence of the bump and dip in the impedance curves on the rotordynamic stability. With the same FE model, speed-dependent impedances are calculated to obtain unbalance frequency response. Finally, a new linear curve-fit approach is developed to model the fluctuating impedances since the unconventional impedance cannot be expressed by the second-order polynomials with the rotordynamic coefficients (stiffness, damping, and mass). In order to validate the newly developed method, a Jeffcott rotor model with the impeller forces is considered and rotordynamic stability analysis is implemented. The results of the analysis show that the existence of the bump and dip in the impedance curves may further destabilize the rotor system.

Copyright © 2016 by ASME
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References

Figures

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Fig. 1

Impedance curves for the conventional wear-ring seal impeller at 2000 rpm (a) radial and (b) tangential for three inlet whirl frequency ratios (WFRs) inlet swirl ratio (ISR)

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Fig. 2

FE model of rotor-bearing system

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Fig. 3

Circular motion of the impeller

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Fig. 4

Cut plane view of three-dimensional eccentric grid of the conventional wear-ring seal impeller

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Fig. 5

Impedance curves at multiple spin speeds

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Fig. 6

Impedances for WFR = 1 at multiple spin speeds: (a) radial impedance and (b) tangential impedance

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Fig. 7

Synchronous unbalance response versus spin speed

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Fig. 8

Simple Jeffcott rotor model including impeller impedances

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Fig. 9

Least square curve-fit impedances of 2000 rpm case (a) tangential impedance and (b) radial impedance

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Fig. 10

Magnitude and phase of D(jΩ)  and E(jΩ) for the approximated quadratic impedances of 2000 rpm case

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Fig. 11

Curve-fit results of D(jΩ)  and E(jΩ) for the approximated impedances of 2000 rpm case

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Fig. 12

Curve-fit results utilizing frequency range segmentation of D(jΩ)  and E(jΩ) for the approximated impedances of 2000 rpm

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Fig. 13

Comparison of system log-dec for the quadratic impedance case versus damping ratio ζ

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Fig. 14

Curve-fit results of 4000 rpm case by transfer function model

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Fig. 15

Curve-fit results of 4000 rpm case by transfer function model with segmentation

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Fig. 16

Comparison of log-dec between the approximate (quadratic) impedances and the original (segmented curve fit) impedances versus damping ratio ζ for 4000 rpm case

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Fig. 17

Log-dec versus damping ratio ζ comparisons for different ISR for 2000 rpm case using the multisegment approach

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Fig. 18

Log-dec versus damping ratio ζ comparisons for different spin speeds using the multisegment approach

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