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RESEARCH PAPERS

High-Pressure Pocket Damper Seals: Leakage Rates and Cavity Pressures

[+] Author and Article Information
Ahmed M. Gamal

Turbomachinery Laboratory, Mechanical Engineering Department, Texas A&M University, College Station, TX 77843ahmedmg@tamu.edu

Bugra H. Ertas

Vibration/Dynamics Laboratory, Physical Sciences Department, General Electric Global Research, Niskayuna, NY 12309ertas@research.ge.com

John M. Vance

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

J. Turbomach 129(4), 826-834 (Sep 03, 2006) (9 pages) doi:10.1115/1.2720871 History: Received August 26, 2006; Revised September 03, 2006

The turbomachinery component of interest in this paper, the pocket damper seal, has the dual purpose of limiting leakage and providing an additional source of damping at the seal location. The rotordynamic coefficients of these seals (primarily the direct stiffness and damping) are highly dependent on the leakage rates through the seals and the pressures in the seals’ cavities. This paper presents both numerical predictions and experimentally obtained results for the leakage and the cavity pressures of pocket damper seals operating at high pressures. The seals were tested with air, at pressures up to 1000psi(6.92MPa), as the working fluid. Earlier flow-prediction models were modified and used to obtain theoretical reference values for both mass flow rates and pressures. Leakage and static pressure measurements on straight-through and diverging-clearance configurations of eight-bladed and twelve-bladed seals were used for code validation and for calculation of seal discharge coefficients. Higher than expected leakage rates were measured in the case of the twelve-bladed seal, while the leakage rates for the eight-bladed seals were predicted with reasonable accuracy. Differences in the axial pitch lengths of the cavities and the blade profiles of the seals are used to explain the discrepancy in the case of the twelve-bladed seal. The analysis code used also predicted the static cavity pressures reasonably well. Tests conducted on a six-bladed pocket damper seal to further investigate the effect of blade profile supported the results of the eight-bladed and twelve-bladed seal tests and matched theoretical predictions with satisfactory accuracy.

Copyright © 2007 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Ten-bladed pocket damper seal (sectioned view)

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Figure 2

Two-bladed flow-rate model

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Figure 3

Annular gas seal test-rig schematic

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Figure 4

Assembled test rig

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Figure 5

Twelve-bladed (left) and eight-bladed (right) pocket damper seals

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Figure 6

Half-section models of the diverging twelve-bladed (left), eight-bladed (center), and six-bladed (right) seals

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Figure 7

Effect of discharge coefficient ratio on static cavity pressures

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Figure 8

Rotor growth at high speeds

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Figure 9

Average leakage error (discharge coefficients 1.1 inlet and 0.95 exit)

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Figure 10

10,200rpm leakage (eight blades, CR=1:1, Cdin=0.866, Cdexit=0.922)

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Figure 11

15,200rpm leakage (eight blades, CR=1:1, Cdin=0.866, Cdexit=0.922)

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Figure 12

20,200rpm leakage (eight blades, CR=1:1, Cdin=0.866, Cdexit=0.922)

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Figure 13

Measured versus predicted leakage (eight blades, CR=1:1.5, Cdin=0.866, Cdexit=1.118)

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Figure 14

Leakage test inlet pressures (eight blades, CR=1:1.5)

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Figure 15

Measured versus predicted leakage (twelve blades, CR=1:2, Cdin=1.517, Cdexit=1.658)

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Figure 16

Leakage overprediction (eight blades, CR=1:1, Cdin=0.866, Cdexit=0.922)

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Figure 17

Leakage over-prediction (eight blades, CR=1:1.5, Cdin=0.866, Cdexit=1.118)

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Figure 18

Leakage overprediction (twelve blades, CR=1:2, Cdin=1.517, Cdexit=1.658)

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Figure 19

Static cavity pressures (eight blades, CR=1:1)

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Figure 20

Static cavity pressures (eight blades, CR=1:1.5)

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Figure 21

Beveled six-bladed seals

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Figure 22

Leakage through six-bladed PDS configurations

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Figure 23

Blade geometry for diverging eight-bladed (upper) and twelve-bladed (lower) seals

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