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Research Papers: Gas Turbines: Structures and Dynamics

A Design to Improve the Effective Damping Characteristics of Hole-Pattern-Stator Annular Gas Seals

[+] Author and Article Information
Dara W. Childs

Turbomachinery Laboratory, Texas A&M University, College Station, TX 77843dchilds@tamu.edu

Yoon-Shik Shin, Brent Seifert

Turbomachinery Laboratory, Texas A&M University, College Station, TX 77843

J. Eng. Gas Turbines Power 130(1), 012505 (Jan 09, 2008) (7 pages) doi:10.1115/1.2771242 History: Received June 13, 2006; Revised August 16, 2006; Published January 09, 2008

Predictions are presented for hole-pattern-stator seals for which the hole depth is varied axially, showing that various depth patterns can significantly improve damping performance in terms of both increasing the seal’s effective damping and reducing its crossover frequency—the frequency at which effective damping changes from positive to negative. Test results are presented for the seal with the best variable hole depth (VHD) pattern showing an increase in peak damping by a factor of 1.6 over a constant hole depth (CHD) design versus predictions of 2.7. The crossover frequency is reduced by approximately 40%. The VHD seal has a significant negative static stiffness that probably arises from a friction-factor-jump phenomenon, not flow path divergence. The VHD seal leaks less than a comparable CHD design.

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Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 1

CHD, HP geometry (5)

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Figure 2

Effective damping versus f

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Figure 3

Effective stiffness versus f

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Figure 4

Measured values versus predictions for the VHD test seal

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Figure 5

Nondimensional measured rotordynamic coefficients for the CHD seal with PR=.45 and the VHD seal with and PR=.50 for ω=20,200rpm, zero preswirl, and Cr=0.20mm

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Figure 6

Leakage coefficient for the VHD seal at Pin=41.4bars and the CHD seal with Pin=70bars for zero preswirl and ω=20,200rpm

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Figure 7

Kxx, Kxy, Cxy, Cxy versus excitation frequency Ω for a CHD seal for Cr=0.20mm, ω=20,200rpm, u0(0)=0.028, and PR=0.45(5).

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