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Research Papers: Gas Turbines: Structures and Dynamics

Rotordynamic Force Coefficients for Three Types of Annular Gas Seals With Inlet Preswirl and High Differential Pressure Ratio

[+] Author and Article Information
B. H. Ertas

 Mechanical Systems, Rotating Equipment Group, GE Research Center, Niskayuna, NY 12390ertas@research.ge.com

A. Delgado

 Mechanical Systems, Rotating Equipment Group, GE Research Center, Niskayuna, NY 12390

G. Vannini

 Conceptual Advanced Mechanical Design, Advanced Technology Organization, GE Oil and Gas, 50127 Florence, Italy

J. Eng. Gas Turbines Power 134(4), 042503 (Jan 27, 2012) (12 pages) doi:10.1115/1.4004537 History: Received April 12, 2011; Revised June 30, 2011; Published January 27, 2012; Online January 27, 2012

The following paper presents and compares rotordynamic force coefficients for three types of non-contact annular gas seals, which include a labyrinth (LABY), honeycomb (HC), and a fully partitioned damper seal (FPDS). These three annular seals represent the typical seal types used in process gas centrifugal compressors at the balance piston location or center seal location to limit internal leakage and ensure a robust rotordynamic design. Tests were conducted on 170.6 mm (6.716 in) diameter seals for rotor speeds up to 15 kprm, inlet air pressure of 6.9 bar (100 psi), ambient back pressure, and with inlet gas preswirl. The three seals were designed to have the same nominal clearance and similar axial lengths. Testing was conducted on a controlled motion test rig possessing non-synchronous excitation capability up to 250 Hz. Three different test methods were employed to give confidence in the rotordynamic coefficients, which include static force deflection tests, mechanical impedance tests, and dynamic cavity pressure tests. Results from experiments compare force coefficients for all seal configurations while paying special attention to the crossover frequencies of the effective damping term. All seals possessed negative effective damping at lower excitation frequencies with inlet preswirl, where the straight-through FPDS possessed the lowest cross over frequency of 40 Hz at 15 krpm. The testing also revealed that the preswirl parameter had significantly more influence on effective damping levels and crossover frequencies when compared to rotor speed.

Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 2

Test seal geometry (dimensions in inches)

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Figure 3

Test rig cross section (dimensions in inches)

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Figure 4

Inlet preswirl and coordinate system convention

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Figure 5

Example static force-deflection tests

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Figure 6

X excitation: Mechanical impedance method

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Figure 7

X excitation: Pressure method 198 Hz FPDS2

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Figure 8

Static stiffness with preswirl and no rotation

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Figure 9

Direct static stiffness with no preswirl

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Figure 10

Cross-coupled static stiffness with no preswirl

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Figure 11

Direct stiffness and damping: 7 krpm and 15 krpm: Mechanical impedance method

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Figure 12

Cross-coupled stiffness 7 krpm and 15 krpm: Mechanical impedance method

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Figure 13

Effective damping 7 krpm and 15 krpm: Mechanical impedance method

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Figure 14

Rotordynamic coefficients: Preswirl versus rotor speed FPDS2

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Figure 15

Cavity level rotordynamic coefficients: FPDS2 0 RPM with preswirl

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Figure 16

Cavity Ceff crossover frequencies: FPDS2

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