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Research Papers: Gas Turbines: Structures and Dynamics

Numerical and Experimental Investigation on the Effect of Swirl Brakes on the Labyrinth Seals

[+] Author and Article Information
Dan Sun

Liaoning Key Laboratory of Advanced Test
Technology for Aerospace Propulsion System,
Shenyang Aerospace University,
Shenyang 110136, China
e-mail: phd_sundan@163.com

Shuang Wang

Liaoning Key Laboratory of Advanced Test
Technology for Aerospace Propulsion System,
Shenyang Aerospace University,
Shenyang 110136, China
e-mail: dameiwuxing@163.com

Cheng-Wei Fei

Department of Mechanical Engineering,
Hong Kong Polytechnic University
Hong Kong, China;
School of Energy and Power Engineering,
Beihang University,
Beijing 100191, China
e-mail: feicw544@163.com

Yan-Ting Ai

Liaoning Key Laboratory of Advanced Test
Technology for Aerospace Propulsion System,
Shenyang Aerospace University,
Shenyang 110136, China
e-mail: ytai@163.com

Ke-Ming Wang

Liaoning Key Laboratory of Advanced Test
Technology for Aerospace Propulsion System,
Shenyang Aerospace University,
Shenyang 110136, China
e-mail: wkm308@126.com

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 May 28, 2015; final manuscript received September 3, 2015; published online October 28, 2015. Editor: David Wisler.

J. Eng. Gas Turbines Power 138(3), 032507 (Oct 28, 2015) (12 pages) Paper No: GTP-15-1178; doi: 10.1115/1.4031562 History: Received May 28, 2015; Revised September 03, 2015

Swirl brake influences the static and rotordynamic characteristics of labyrinth seal which are important in the prediction of turbomachine stability. To study the influence of the swirl brakes on improving seal stability, the effects of swirl brakes on the static and rotordynamic characteristics of labyrinth seals were investigated by the combination of numerical simulation and experiment. First, it was performed to the effects of swirl brake on the static flow characteristics of labyrinth seal with swirl ratio and pressure distribution based on computational fluid dynamics (CFD). And then a comparison between leakage predicted by the CFD model and measurement was presented to verify the accuracy of the simulation. Moreover, an experiment was implemented to analyze the rotordynamic characteristics of labyrinth seal using an improved impedance method based on an unbalanced synchronous excitation method on a rotor test rig. The influences of swirl brake density, length, inlet/outlet pressure ratio, and rotating speed were measured and discussed, respectively. The CFD numerical results show that the swirl brake effectively reduces the seal swirl ratio (∼60–75% less), circumferential pressure difference (∼25–85% less) so that the seal destabilizing forces decrease. With the increasing of the swirl vanes density and length, the seal leakage drops (∼8–20% less). The experimental rotordynamic characteristics results show that it is more obvious to reduce the cross-couple stiffness (∼50–300% less) and increase the direct damping (∼50–60% larger) with the increasing in the number and length of the swirl vanes, and thus the swirl brake improves the seal rotordynamic stability. The efforts of this paper provide a useful insight to clearly understand the effects of swirl brakes on the labyrinth seal static and rotordynamic characteristics, which is beneficial to improve the design of annular seals.

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References

Figures

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Fig. 1

Cross section view of a centrifugal compressor

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Fig. 2

Seal with swirl vanes

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Fig. 3

Different patterns of swirl brakes: (a) long swirl vanes (40) and (b) short swirl vanes(30)

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Fig. 4

Dimensions of the seal with swirl vanes: (a) dimensions of the seal and (b) scheme of the swirl vanes size

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Fig. 5

Computational domain and boundary conditions: (a) periodic model and (b) 3D eccentric CFD model

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Fig. 6

Seals mesh model: (a) periodic model and (b) 3D eccentric CFD model

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Fig. 7

Schematic diagram of the seal test rig

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Fig. 8

The seal installation type and air inlet type on seal test rig: (a) the physical map of seal installation and (b) schematic diagram of the air inlet type

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Fig. 9

Photo of sensor placement

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Fig. 10

Schematic diagram of measurement system

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Fig. 11

Schematic diagram of the seal force equivalent model

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Fig. 12

Schematic diagram of seal-force identification model

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Fig. 13

Shaker excitation experiment: (a) shaker excited in x direction and (b) shaker excited in y direction

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Fig. 14

Motion orbit of the test cylinder: (a) motion orbit of the test cylinder (ω = 1200 rpm) and (b) motion orbit of the test cylinder (ω = 2000 rpm)

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Fig. 15

Flow field for seals (inlet pressure = 0.8 MPa; outlet pressure = 0.1 MPa; Rotor speed = 3000 rpm): (a) pressure distribution and (b) velocity distribution

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Fig. 16

Two lines for the value of tangential velocity

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Fig. 17

Swirl ratio distribution for the seals with different swirl vanes (inlet pressure = 0.8 MPa; outlet pressure = 0.5 MPa; and rotor speed = 3000 rpm): (a) line at seal entrance and (b) line at seal cavity

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Fig. 18

Schematic diagram of sections for the value of pressure

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Fig. 19

Pressure distribution for the seals with different swirl vanes (inlet pressure = 0.8 MPa; outlet pressure = 0.5 MPa; rotor speed = 3000 rpm): (a) without swirl vane, (b) with swirl vanes (20), and (c) pressure distribution for the seals with different swirl vanes

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Fig. 20

Influence of inlet/outlet pressure ratio on leakage (outlet pressure = 0.1 MPa; rotor speed = 3000 rpm)

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Fig. 21

Rotordynamic coefficients as a function of rotating speed: (a) direct stiffness coefficients; (b) cross stiffness coefficients; (c) direct damping coefficients; and (d) cross damping coefficients

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Fig. 22

Rotordynamic coefficients as a function of inlet/outlet pressure ratio: (a) direct stiffness coefficients; (b) cross stiffness coefficients; (c) direct damping coefficients; and (d) cross damping coefficients

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