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Research Papers: Gas Turbines: Structures and Dynamics

# Numerical Investigations on the Leakage and Rotordynamic Characteristics of Pocket Damper Seals—Part II: Effects of Partition Wall Type, Partition Wall Number, and Cavity Depth

[+] Author and Article Information
Zhigang Li

Institute of Turbomachinery,
Xi'an Jiaotong University,
School of Energy & Power Engineering,
Xi'an Jiaotong University,
Xi'an 710049, China

Jun Li

Institute of Turbomachinery,
School of Energy & Power Engineering,
Xi'an Jiaotong University,
Xi'an 710049, China
Collaborative Innovation Center of
Beijing 100191, China
e-mail: junli@mail.xjtu.edu.cn

Zhenping Feng

Institute of Turbomachinery,
School of Energy & Power Engineering,
Xi'an Jiaotong University,
Xi'an 710049, China

1Corresponding author.

Contributed by the Structures and Dynamics Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received July 11, 2014; final manuscript received July 17, 2014; published online September 30, 2014. Editor: David Wisler.

J. Eng. Gas Turbines Power 137(3), 032504 (Sep 30, 2014) (13 pages) Paper No: GTP-14-1374; doi: 10.1115/1.4028374 History: Received July 11, 2014; Revised July 17, 2014

## Abstract

Effects of partition wall type, partition wall number and cavity depth on the leakage and rotordynamic characteristics of the pocket damper seal (PDS) were numerically investigated using a presented 3D transient computational fluid dynamics (CFD) method based on the multifrequency elliptical whirling orbit model. The accuracy and availability of this transient CFD method and the multifrequency elliptical whirling orbit model were demonstrated with the experimental data of the experimental eight-bladed fully partitioned pocket damper seal (FPDS). The leakage flow rates and frequency-dependent rotordynamic coefficients of PDS were computed for two types of partition wall (namely conventional PDS and fully partitioned PDS), four partition wall numbers including the labyrinth seal (no partition wall) and six cavity depths including the plain smooth seal (zero cavity depth) at operational conditions with or without inlet preswirl and 15,000 rpm rotational speed. The numerical results show that the FPDS has the similar leakage performance and more superior stability capacity than the conventional PDS. The FPDS possesses slightly larger leakage flow rate (∼2.6–4.0% larger) compared to the labyrinth seal. Eight is a preferable value for the partition wall number to gain the best leakage performance of the FPDS with the least manufacturing cost. The FPDS possesses significantly larger stiffness and damping than the labyrinth seal. Increasing partition wall number results in a significant increase in the direct stiffness but limited desirable effect on the effective damping. The FPDS possesses the lowest leakage flow rate when the cavity depth is about 2.0 mm. Compared to the plain smooth seal, the FPDS possesses larger positive direct stiffness and significantly less direct damping and effective damping. Increasing cavity depth results in a significant decrease in the stabilizing direct damping and the magnitude of the destabilizing cross-coupling stiffness. $H=$ 3.175 mm is a preferable value of the cavity depth for which the effective damping of the FPDS is largest, especially for the concerned frequencies (80–120 Hz) where most multistage high-pressure centrifugal compressors have stability problem.

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## Figures

Fig. 1

Fig. 2

Eight-bladed, eight-pockets, conventional PDS versus fully partitioned PDS

Fig. 3

Labyrinth seal versus eight-bladed fully partitioned PDS with different partition wall numbers

Fig. 4

Plain smooth seal versus eight-bladed fully partitioned PDS with different cavity depths

Fig. 5

Computational models of the fully partitioned PDS

Fig. 6

Rotordynamic coefficients versus vibration frequency at different partition wall types (NPS = zero preswirl, PS = 60 m/s preswirl)

Fig. 7

Cavity dynamic pressure and seal response force of the conventional PDS versus the fully partitioned PDS (xexcitation, zero preswirl)

Fig. 8

Seal leakage flow rate versus partition wall number

Fig. 9

Rotordynamic coefficients versus vibration frequency at different partition wall numbers (with zero preswirl)

Fig. 10

Rotordynamic coefficients versus vibration frequency at different partition wall numbers (with 60 m/s preswirl)

Fig. 11

Static pressure contours on the cross section through the middle of cavity 3 and the phasor diagram of the response force for the labyrinth seal and the fully partitioned PDS at different partition wall numbers (x excitation, 60 m/s preswirl, T = 0.1s)

Fig. 12

Seal leakage flow rate versus cavity depth

Fig. 13

Rotordynamic coefficients versus vibration frequency at different cavity depths (with zero preswirl)

Fig. 14

Static pressure contours on the cross section through the middle of cavity 3 and phasor diagram of the response force for the plain smooth seal and fully partitioned PDS at different cavity depths (zero preswirl, x excitation, T = 0.1s)

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