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TECHNICAL PAPERS: Gas Turbines: Structures and Dynamics

A Bulk Flow Model for Off-Centered Honeycomb Gas Seals

[+] Author and Article Information
Thomas Soulas, Luis San Andres

Mechanical Engineering Department, Texas A&M University, College Station, TX 77843-3123

The empirical values for the Blasius’ rotor and stator friction coefficient parameters used in Kleynhans’ model are nr=0.0586, mr=0.2170, ns=0.0785, and ms=0.1101 respectively.

Weatherwax (15) presents honeycomb seal test results for increasing rotor eccentricities with comparisons to predictions from the present model.

J. Eng. Gas Turbines Power 129(1), 185-194 (Mar 01, 2002) (10 pages) doi:10.1115/1.2227031 History: Received October 01, 2001; Revised March 01, 2002

A computational analysis for prediction of the static and dynamic forced performance of gas honeycomb seals at off-centered rotor conditions follows. The bulk-flow analysis, similar to the two-control volume flow model of Kleynhans and Childs (1997, “The Acoustic Influence of Cell Depth on the Rotordynamic Characteristics of Smooth-Rotor/Honeycomb-Stator Annular Gas Seals  ,” ASME J. Eng. Gas Turbines Power, 119, pp. 949–957), is brought without loss of generality into a single-control volume model, thus simplifying the computational process. The formulation accommodates the honeycomb effective cell depth, and existing software for annular pressure seals and is easily upgraded for damper seal analysis. An analytical perturbation method for derivation of zeroth- and first-order flow fields renders the seal equilibrium response and frequency-dependent dynamic force impedances, respectively. Numerical predictions for a centered straight-bore honeycomb gas seal shows good agreement with experimentally identified impedances, hence validating the model and confirming the paramount influence of excitation frequency on the rotordynamic force coefficients of honeycomb seals. The effect of rotor eccentricity on the static and dynamic forced response of a smooth annular seal and a honeycomb seal is evaluated for characteristic pressure differentials and rotor speeds. Leakage for the two seal types increases slightly as the rotor eccentricity increases. Rotor off-centering has a pronounced nonlinear effect on the predicted (and experimentally verified) dynamic force coefficients for smooth seals. However, in honeycomb gas seals, even large rotor center excursions do not sensibly affect the effective local film thickness, maintaining the flow azimuthal symmetry. The current model and predictions thus increase confidence in honeycomb seal design, operating performance, and reliability in actual applications.

FIGURES IN THIS ARTICLE
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Copyright © 2007 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Honeycomb annular seal and rotating shaft—Two control volume model

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Figure 2

Measured and predicted (real and imaginary parts) dynamic impedances (D) and (E) for a honeycomb seal versus excitation frequency. Medium speed/medium pressure (PD∕PS=0.50), rotor centered condition (ε=0).

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Figure 3

Leakage (Q) predictions versus rotor speed/supply pressure for smooth and honeycomb gas seals (PD∕PS=0.50), rotor eccentricity ratio (eX∕c*) increases

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Figure 4

Dynamic direct stiffness coefficient KXX=Re(D) versus excitation frequency for smooth and honeycomb seals (PD∕PS=0.50) as a function of rotor eccentricity (eX∕c*)—LSLP, MSMP, and HSHP configurations

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Figure 5

Dynamic direct stiffness coefficients KXX=Re(D) and KYY=Re(F) versus excitation frequency for smooth and honeycomb seals (PD∕PS=0.50), eccentricity ratio eX∕c*=0.5—LSLP configuration

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Figure 6

Dynamic cross-coupled stiffness coefficient KXY=Re(E) versus excitation frequency for smooth and honeycomb seals (PD∕PS=0.50) as a function of rotor eccentricity (eX∕c*)—LSLP, MSMP, and HSHP configurations

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Figure 7

Dynamic cross-coupled stiffness coefficients KXY=Re(E) and −KYX=−Re(G) versus excitation frequency for smooth and honeycomb seals, (PD∕PS=0.50) and eccentricity ratio eX∕c*=0.5—LSLP configuration

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Figure 8

Coefficient ωCXX=Im(D) versus excitation frequency for smooth and honeycomb seals (PD∕PS=0.50) as a function of rotor eccentricity (eX∕c*)—LSLP, MSMP, and HSHP configurations

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Figure 9

Coefficients ωCXX=Im(D) and ωCYY=Im(F) versus excitation frequency for smooth and honeycomb seals, (PD∕PS=0.50) and eccentricity ratio eX∕c*=0.5—LSLP configuration

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Figure 10

Effective stiffness coefficient (KXeff) versus excitation frequency for smooth and honeycomb seals (PD∕PS=0.50) as a function of rotor eccentricity (eX∕c*). MSMP configuration

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Figure 11

Effective damping coefficient (CXeff) versus excitation frequency for smooth and honeycomb seals (PD∕PS=0.50) as a function of rotor eccentricity (eX∕c*). MSMP configuration

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