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TECHNICAL PAPERS

Rotordynamic Force Coefficients of Pocket Damper Seals

[+] Author and Article Information
B. Ertas

Vibrations/Dynamics Laboratory, Rotating Equipment Group, GE Global Research, 1 Research Circle, Niskayuna, NY 12309ertas@research.ge.com

A. Gamal

Mechanical Engineering Department, Texas A&M University, College Station, TX 77843-3123ajmg@tamu.edu

J. Vance

Mechanical Engineering Department, Texas A&M University, College Station, TX 77843-3123jvance@tamu.edu

J. Turbomach 128(4), 725-737 (Feb 01, 2006) (13 pages) doi:10.1115/1.2221327 History: Received October 01, 2005; Revised February 01, 2006

This paper presents measured frequency dependent stiffness and damping coefficients for 12-bladed and 8-bladed pocket damper seals (PDS) subdivided into four different seal configurations. Rotating experimental tests are presented for inlet pressures at 69 bar (1000 psi), a frequency excitation range of 20–300 Hz, and rotor speeds up to 20,200 rpm. The testing method used to determine direct and cross-coupled force coefficients was the mechanical impedance method, which required the measurement of external shaker forces, system accelerations, and motion in two orthogonal directions. In addition to the impedance measurements, dynamic pressure responses were measured for individual seal cavities of the eight-bladed PDS. Results of the frequency dependent force coefficients for the four PDS designs are compared. The conclusions of the tests show that the eight-bladed PDS possessed significantly more positive direct damping and negative direct stiffness than the 12-bladed seal. The results from the dynamic pressure response tests show that the diverging clearance design strongly influences the dynamic pressure phase and force density of the seal cavities. The tests also revealed the measurement of same-sign cross-coupled (cross-axis) stiffness coefficients for all seals, which indicate that the seals do not produce a destabilizing influence on rotor-bearing systems.

Copyright © 2006 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Twelve bladed PDS

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Figure 2

Eight bladed PDS

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Figure 3

High-pressure annular gas seal test rig (12)

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Figure 4

Stator housing isometric view with instrumentation

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Figure 5

Stator housing front and side views

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Figure 6

Dynamic measurements

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X and Y direction pseudorandom forced excitations

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Figure 8

Experimental measurements: Impedance method (12)

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Figure 10

Dynamic cavity pressures

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Figure 11

Experimental measurements: Dynamic pressure response method

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Figure 12

Phasor plot: Dynamic pressure response

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Figure 13

Direct stiffness and direct damping: 8 bladed PDS 10,200rpm

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Figure 14

Direct stiffness and direct damping: 8 bladed PDS 20,200rpm

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Figure 15

Direct stiffness and direct damping: 8 bladed PDS versus 12 bladed PDS

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Figure 16

Cross-coupled stiffness: 8 bladed PDS

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Figure 17

Cross-coupled stiffness: 12 bladed PDS

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Figure 18

Cross-coupled damping: 12 bladed PDS

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Figure 19

Cavity pressure phase and force density: 8 bladed PDS

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Figure 20

Cavity coefficients: 8 bladed PDS

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