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Research Papers: Gas Turbines: Structures and Dynamics

The Impact of Real Gas Properties on Predictions of Static and Rotordynamic Properties of the Annular Gas Seals for Injection Compressors

[+] Author and Article Information
Yoon-Shik Shin

Purdue University

Dara W. Childs

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

J. Eng. Gas Turbines Power 130(4), 042504 (Apr 29, 2008) (8 pages) doi:10.1115/1.2904891 History: Received October 03, 2007; Revised October 04, 2007; Published April 29, 2008

Predictions are presented for an annular gas seal that is representative of the division-wall seal of a back-to-back compressor or the balance-piston seal of an in-line compressor. A two-control-volume bulk-flow model is used including the axial and circumferential momentum equations and the continuity equations. The basic model uses a constant-temperature prediction (ISOT) and an ideal gas law as an equation of state. Two variations are used: adding the energy equation with an ideal gas law (IDEAL), and adding the energy equation with real gas properties (REAL). The energy equations assume adiabatic flow. The ISOT model has been used for prior calculations. Concerning predictions of static characteristics, the calculated mass leakage rates were, respectively, 9.46 kg∕s, 9.55 kg∕s, and 7.87 kg∕s for ISOT, IDEAL, and REAL. For rotordynamic coefficients, predicted effective stiffness coefficients are comparable for the models at low excitation frequencies. At running speed, REAL predictions are roughly 40% lower than ISOT, which could result in lower predicted critical speeds. Predicted effective damping coefficients are also generally comparable. REAL and IDEAL predictions for the crossover frequency are approximately 20% lower than ISOT. REAL predictions for effective damping are modestly lower in the frequency range of 40–50% of running speed where higher damping values are desired.

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Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 1

Geometry of HP seal (6)

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Figure 2

Flow in and flow out of the control volumes (6)

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Figure 3

Calculated versus measured mass leakage results for a HC-stator seal, sealing air

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Figure 4

Density distribution versus axial position

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Figure 5

Temperature distribution versus axial position

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Figure 6

Speed of sound for the three models

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Figure 7

Effective stiffness Keff(f) versus nondimensional frequency f

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Figure 8

Cross-coupled stiffness k(f) versus nondimensional frequency f

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Figure 9

Direct damping C(f) versus nondimensional frequency f

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Figure 10

Effective damping Ceff(f) versus nondimensional frequency f

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