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RESEARCH PAPERS

Rotordynamic-Coefficients and Static (Equilibrium Loci and Leakage) Characteristics for Short, Laminar-flow Annular Seals

[+] Author and Article Information
Dara W. Childs

Turbomachinery Laboratory, Texas A&M University, College Station, TXdchilds@mengr.tamu.edu

Luis E. Rodriguez

 Sulzer Hickham, La Porte, TX

Vito Cullotta

 Mustang Engineering, TX

Adnan Al-Ghasem, Matthew Graviss

Mechanical Engineering Department, Texas A&M University, College Station, TX

J. Tribol 128(2), 378-387 (Sep 28, 2005) (10 pages) doi:10.1115/1.2164468 History: Received April 26, 2005; Revised September 28, 2005

Test results are presented for laminar-flow seals that are representative of buffered-flow oil seals in centrifugal compressors. The seals are short (LD0.21), with a diameter of 117mm and a clearance-to-radius ratio 0.0007. A smooth seal, a seal with one central groove, and a seal with three grooves were tested. Groove geometries employed are representative of industrial practice for compressors with a groove-depth to clearance ratio on the order of 6. Tests were conducted at 4000, 7000, and 10,000rpm shaft speed with delta pressures across the seals of 21, 45, and 69bars. For all cases, the flow was laminar. The seals were tested from a centered position out to an eccentricity ratio of 0.7. Static data included leakage and equilibrium loci for a range of loads. Direct and cross-coupled stiffness and damping coefficients and direct mass coefficients were determined from dynamic tests. For the smooth seal, comparisons between measurements and predictions were reasonable for the direct and cross-coupled stiffness and damping coefficients; however, measured added mass coefficients were roughly ten times larger than predicted. Predictions for the grooved seals from a “deep-groove” model that assumed zero pressure oscillations in the grooves greatly over predicted the influence of the grooves. In a centered position, smooth and grooved seals had comparable leakage performance. At higher eccentricity ratios, the grooved seals leaked modestly more. For eccentricity ratios less than approximately 0.3, the grooved seals and the smooth seal had qualitatively similar static and dynamic characteristics. In terms of cross-coupled stiffness coefficients, the grooved seals were less stable than the smooth seal at eccentricity ratios greater than approximately 0.5 but had significantly lower cross-coupled coefficients at reduced eccentricity ratios between zero and 0.3. A grooved centered seal is more stable than a smooth centered seal. The smooth seal had higher damping than the grooved seals and had moderately better centering capabilities.

Copyright © 2006 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Oil seal assembly (9)

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Figure 2

Side view of the oil seal test rig

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Figure 3

End view of the oil seal test rig

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Figure 4

Test seal geometries

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Figure 7

Measured leakage for the smooth seal

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Figure 8

Measured leakage for the 3-groove seal

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Figure 13

cxx, cyy and cxy, cyx versus ε0 for the smooth seal at 7000rpm and three differential pressures. Solid lines are measurements, dashed lines are predictions from Code A.

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Figure 14

Measured direct stiffness coefficients for the smooth- and 3-groove seals at 7000rpm

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Figure 17

Measured damping coefficients for the smooth- and 3-groove seals at 7000rpm

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Figure 18

Added-mass coefficients for 3-groove seal at 7000rpm

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Figure 10

Real and imaginary components of the dynamic stiffness coefficients for ω=10,000rpm, Ps=69bar, and ε0=0.5

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Figure 9

Real and imaginary components of the dynamic stiffness coefficients for ω=10,000rpm, Ps=45bar, and ε0=0.3

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Figure 6

Three-groove seal loci for 21 (LP), 45 (MP), and 69 (HP) bar supply pressures

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Figure 5

Smooth seal loci for 21 (LP), 45 (MP), and 69 (HP) bar supply pressures

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Figure 12

cxx,cyy and cxy,cyx versus ε0 for the smooth seal at 7000rpm and three differential pressures. Solid lines are measurements, dashed lines are predictions from Code A.

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Figure 11

kxx,kyy and kxy,kyx versus ε0 for the smooth seal at 7000rpm and three differential pressures. Solid lines are measurements, dashed lines are predictions from Code A.

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Figure 16

Measured cross-coupled stiffness coefficients for the smooth- and 3-groove seals at 7000rpm at lower eccentricity ratios

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Figure 15

Measured cross-coupled stiffness coefficients for the smooth- and 3-groove seals at 7000rpm

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