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Research Papers: Gas Turbines: Structures and Dynamics

A Numerical Investigation of the Effect of Inlet Preswirl Ratio on Rotordynamic Characteristics of Labyrinth Seal

[+] Author and Article Information
Tomohiko Tsukuda

Power and Industrial Systems Research and
Development Center,
Toshiba Corporation,
Yokohama 230-0045, Japan
e-mail: tomohiko.tsukuda@toshiba.co.jp

Toshio Hirano

Power and Industrial Systems Research and
Development Center,
Toshiba Corporation,
Yokohama 230-0045, Japan
e-mail: toshio1.hirano@toshiba.co.jp

Cori Watson

Rotating Machinery and Controls
(ROMAC) Laboratory,
Department of Mechanical and
Aerospace Engineering,
University of Virginia,
Charlottesville, VA 22904-4746
e-mail: cw2xw@virginia.edu

Neal R. Morgan

Rotating Machinery and Controls
(ROMAC) Laboratory,
Department of Mechanical and
Aerospace Engineering,
University of Virginia,
Charlottesville, VA 22904-4746
e-mail: nrm6 dr@virginia.edu

Brian K. Weaver

Rotating Machinery and Controls
(ROMAC) Laboratory,
Department of Mechanical and
Aerospace Engineering,
University of Virginia,
Charlottesville, VA 22904-4746
e-mail: bkw3q@virginia.edu

Houston G. Wood

Rotating Machinery and Controls
(ROMAC) Laboratory,
Department of Mechanical and
Aerospace Engineering,
University of Virginia,
Charlottesville, VA 22904-4746
e-mail: hgw9p@virginia.edu

Contributed by the Structures and Dynamics Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received September 26, 2017; final manuscript received October 27, 2017; published online May 14, 2018. Editor: David Wisler.

J. Eng. Gas Turbines Power 140(8), 082506 (May 14, 2018) (10 pages) Paper No: GTP-17-1530; doi: 10.1115/1.4039360 History: Received September 26, 2017; Revised October 27, 2017

Full three-dimensional (3D) computational fluid dynamics (CFD) simulations are carried out using ANSYS cfx to obtain the detailed flow field and to estimate the rotordynamic coefficients of a labyrinth seal for various inlet swirl ratios. Flow fields in the labyrinth seal with the eccentricity of the rotor are observed in detail and the detailed mechanisms that increase the destabilizing forces at high inlet swirl ratios are discussed based on the fluid governing equations associated with the flow fields. By evaluating the contributions from each term of the governing equation to cross-coupled force, it is found that circumferential velocity and circumferential distribution of axial mass flow rate play key roles in generating cross-coupled forces. In the case that circumferential velocity is high and decreases along the axial direction, all contributions from each term are positive cross-coupled force. On the other hand, in the case that circumferential velocity is low and increases along the axial direction, one contribution is positive but the other is negative. Therefore, cross-coupled force can be negative in the local chamber depending on the balance even if circumferential velocity is positive. CFD predictions of cross-coupled stiffness coefficients and direct damping coefficients show better agreement with experimental results than a bulk flow model does by considering the force on the rotor in the inlet region. Cross-coupled stiffness coefficients derived from the force on the rotor in the seal section agree well with those of the bulk flow model.

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References

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Figures

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Fig. 3

A rotating reference frame attached to the whirling rotor

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Fig. 4

Mass-averaged circumferential velocity distributions along the axial direction for various inlet swirl ratios

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Fig. 2

Inlet geometry, boundary conditions, and radial velocity distribution

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Fig. 1

Analytical region and mesh: (a) cross-sectional view and three-dimensional view of the analytical region and mesh and (b) geometry and mesh of labyrinth seal

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Fig. 5

Distributions of pressure perturbation on the rotor surface in the θ direction (a) at z = 0.010 m, (b) at z = 0.023 m, and (c) at z = 0.092 m

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Fig. 6

Axial velocity distribution and velocity vectors on the r-z plane in the second chamber of the seal section at θ = 90 deg for an inlet swirl ratio of 0.65

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Fig. 7

Non-dimensional mass flow rate per circumferential length at θ = 0 deg, 90 deg, 180 deg, and 270 deg for an inlet swirl ratio of 0.65

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Fig. 8

Circumferential velocity distribution and velocity vectors on the r-z plane in the second chamber of the seal section at θ = 90 deg for an inlet swirl ratio of 0.65

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Fig. 9

Mass-averaged circumferential velocity along the axial direction for each inlet swirl ratio

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Fig. 10

Mass-averaged circumferential velocity at each circumferential positon for an inlet swirl ratio of 0.65

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Fig. 11

Circumferential velocity distribution in the r-θ plane at z = z3 for an inlet swirl ratio of 0.65

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Fig. 12

Cavity control volume

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Fig. 13

Forces on the control volume

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Fig. 14

Relationship between circumferential pressure distribution and direction of rotor force

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Fig. 15

Analytical region and boundary conditions of the simple CFD model

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Fig. 16

Pressure perturbations obtained from the simple CFD model compared with the results in Fig. 5(b)

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Fig. 17

Relations between the tangential forces and the whirl speed for each inlet swirl ratio

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Fig. 18

Relations between the radial forces and the whirl speed for each inlet swirl ratio

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Fig. 19

Comparisons of cross-coupled stiffness coefficients

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Fig. 20

Comparisons of leakage mass flow rate

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Fig. 21

Comparisons of direct damping coefficients

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Fig. 22

Comparisons of direct stiffness coefficients

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Fig. 23

Comparisons of cross-coupled damping coefficients

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