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Research Papers

Impact Analysis of Pocket Damper Seal Geometry Variations on Leakage Performance and Rotordynamic Force Coefficients Using Computational Fluid Dynamics

[+] Author and Article Information
Clemens Griebel

Institute for Energy Systems,
Technical University of Munich,
Garching 85748, Germany
e-mail: clemens.griebel@tum.de

Manuscript received June 25, 2018; final manuscript received June 29, 2018; published online December 4, 2018. Editor: Jerzy T. Sawicki.

J. Eng. Gas Turbines Power 141(4), 041024 (Dec 04, 2018) (9 pages) Paper No: GTP-18-1340; doi: 10.1115/1.4040749 History: Received June 25, 2018; Revised June 29, 2018

In this paper, different notch and partition wall arrangements of a fully partitioned pocket damper seal (FPDS) are investigated using computational fluid dynamics (CFD). The CFD model is derived for a baseline FPDS design reflecting the full sealing configuration with a structured mesh. Steady-state simulations are performed for eccentric rotor position and different operational parameters. The results are validated using experimental cavity pressure measurements. In transient computations, rotor whirl is modeled as a circular motion around an initial eccentricity using a moving mesh technique. Different whirl frequencies are computed to account for the frequency-dependent behavior of damper seals. The stiffness and damping coefficients are evaluated from the impedances in the frequency domain using a fast Fourier transform. The validated model is then transferred to varying designs. In addition to the baseline design, six different notch arrangements with constant clearance ratio were modeled. Moreover, two partition wall design variations were studied based on manufacturability considerations. Predicted leakage as well as frequency-dependent stiffness and damping coefficients are presented and the impact of geometry variations on these parameters is discussed. The results suggest that a single centered notch is favorable and indicate considerably higher effective damping for a design with staggered partition walls. A rounded partition wall design with significantly eased manufacturing reveals good performance.

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References

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Figures

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Fig. 1

Pocket damper seal (PDS, left) and fully partitioned pocket damper seal (FPDS, right)

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Fig. 2

Fully partitioned pocket damper seal geometry variations: notch configurations

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Fig. 3

Fully partitioned pocket damper seal geometry variations: partition wall configurations

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Fig. 4

Schematic of the no-whirl test rig with test seal casing and air supply system

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Fig. 5

Computational grid for the baseline FPDS model with sectional planes of fluid domain

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Fig. 6

Setup of the flow domain with velocity distribution and indicative streamlines

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Fig. 7

Rotor motion scheme used in transient simulations: forward whirl

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Fig. 12

Predicted stiffness coefficients compared for all seal geometries

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Fig. 11

Axial velocity component profile in outlet blade notches: flow narrowing

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Fig. 10

Predicted leakage compared for all seal geometries

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Fig. 9

Experimental and predicted leakage for baseline FPDS at different inlet pressures

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Fig. 8

Experimental and predicted axial pressure distribution on stator wall of baseline FPDS at minimum and maximum clearance

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Fig. 13

Predicted damping coefficients compared for all seal geometries

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Fig. 14

Predicted effective damping compared for all seal geometries

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