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Research Papers: Gas Turbines: Structures and Dynamics

The Effects of Fluid Preswirl and Swirl Brakes Design on the Performance of Labyrinth Seals

[+] Author and Article Information
Alexandrina Untaroiu

Laboratory for Turbomachinery and Components,
Department of Biomedical
Engineering and Mechanics,
Virginia Tech,
Norris Hall, Room 324,
Virginia Tech 495 Old Turner Street,
Blacksburg, VA 24061
e-mail: alexu@vt.rdu

Hanxiang Jin

Laboratory for Turbomachinery and Components,
Department of Biomedical
Engineering and Mechanics,
Virginia Tech,
Norris Hall, Room 107,
Virginia Tech 495 Old Turner Street,
Blacksburg, VA 24061
e-mail: hj3dy@vt.edu

Gen Fu

Laboratory for Turbomachinery and Components,
Department of Biomedical
Engineering and Mechanics,
Virginia Tech,
Norris Hall, Room 107,
Virginia Tech 495 Old Turner Street,
Blacksburg, VA 24061
e-mail: gen8@vt.edu

Vahe Hayrapetiau

Flowserve Corporation,
2300 E Vernon Avenue,
Vernon, CA 90058
e-mail: vhayrapetian@flowserve.com

Kariem Elebiary

Flowserve Corporation,
2300 E Vernon Avenue,
Vernon, CA 90058,
e-mail: kelebiary@flowserve.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 October 31, 2017; final manuscript received December 12, 2017; published online April 25, 2018. Editor: David Wisler.

J. Eng. Gas Turbines Power 140(8), 082503 (Apr 25, 2018) (9 pages) Paper No: GTP-17-1591; doi: 10.1115/1.4038914 History: Received October 31, 2017; Revised December 12, 2017

In noncontact annular labyrinth seals used in turbomachinery, fluid prerotation in the direction of shaft rotation effectively increases fluid velocity in the circumferential direction and generates fluid forces with potential destabilizing effects to be exerted on the rotor. Swirl brakes are typically employed to reduce the fluid prerotation at the inlet of the seal. The inlet flow separates as it follows the swirl brakes, and the ratio between tangential component of the velocity at the seal, and the velocity of the rotor surface varies consequently. Effective swirl brakes can significantly suppress the destabilizing fluid forces as it is effectively reducing the tangential velocity. The literature shows that leakage rate can also be reduced by using swirl brakes with “negative-swirl.” In this study, a labyrinth seal with inlet swirl brakes is selected from the literature and considered the baseline design. The seal performance is evaluated using ANSYS-cfx. The design of experiments (DOEs) approach is used to investigate the effects of various design variables on the seal performance. The design space consists of the swirl brake's length, width, curvature at the ends, the tilt angle, as well as the number of swirl brakes in the circumferential direction. Simple random sampling method with Euclidean distances for the design matrix is used to generate the design points. Steady-state computational fluid dynamics simulations are then performed for each design point to analyze the performance of the swirl brakes. Quadratic polynomial fitting is used to evaluate the sensitivity of the average circumferential velocity with respect to the design variables, which gives a qualitative estimation for the performance of the swirl brakes. These results assist in creating a better understanding of which design variables are critical and more effective in reduction of the destabilizing forces acting on the rotor, and thus will support the swirl brake design for annular pressure seals.

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References

Benckert, H. , and Wachter, J. , 1980, “ Flow Induced Spring Constants of Labyrinth Seals,” The Second International Conference on Vibrations Rotating Machinery, Cambridge, UK, Sept. 1–4, pp. 53–63.
Benckert, H. , and Wachter, J. , 1980, “ Flow Induced Spring Coefficients of Labyrinth Seals for Applications in Rotor Dynamics,” The Rotordynamic Instability Problems in High-Performance Turbomachinery Workshop, College Station, TX, May 12–14, pp. 189–212. https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19800021216.pdf
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Moore, J. , Walker, S. , and Kuzdal, M. , 2002, “ Rotordynamic Stability Measurement During Full-Load, Full-Pressure Testing of a 6000 Psi Reinjection Centrifugal Compressor,” 31st Turbomachinery Symposium, Houston, TX, pp. 29–38. http://oaktrust.library.tamu.edu/handle/1969.1/163317
Weatherwax, M. , and Childs, D. W. , 2003, “ Theory Versus Experiment for the Rotordynamic Characteristics of a High Pressure Honeycomb Annular Gas Seal at Eccentric Positions,” ASME J. Tribol., 125(2), pp. 422–429. [CrossRef]
Picardo, A. , and Childs, D. W. , 2005, “ Rotordynamic Coefficients for a Tooth-on-Stator Labyrinth Seal at 70 Bar Supply Pressures: Measurements Versus Theory and Comparisons to a Hole-Pattern Stator Seal,” ASME J. Eng. Gas Turbines Power, 127(4), pp. 843–855. [CrossRef]
Gans, B. , 2007, “ Reverse-Swirl Brakes Retrofitting With Brush Seals,” Turbomach. Int., pp. 48–49.
Brown, P. D. , and Childs, D. W. , 2012, “ Measurement Versus Predictions of Rotordynamic Coefficients of a Hole-Pattern Gas Seal With Negative Preswirl,” ASME J. Eng. Gas Turbines Power, 134(12), p. 122503. [CrossRef]
Migliorini, P. J. , Untaroiu, A. , Wood, H. G. , and Allaire, P. E. , 2012, “ A Computational Fluid Dynamics/Bulk-Flow Hybrid Method for Determining Rotordynamic Coefficients of Annular Gas Seals,” ASME J. Tribol., 134(2), p. 022202. [CrossRef]
Untaroiu, A. , Hayrapetian, V. , Untaroiu, C. D. , Wood, H. G. , Schiavello, B. , and McGuire, J. , 2013, “ On the Dynamic Properties of Pump Liquid Seals,” ASME J. Fluid Eng., 135(5), p. 051104. [CrossRef]
Mehta, N. J. , and Childs, D. W. , 2013, “ Measured Comparison of Leakage and Rotordynamic Characteristics for a Slanted-Tooth and a Straight-Tooth Labyrinth Seal,” ASME J. Eng. Gas Turbines Power, 136(1), p. 012501. [CrossRef]
Migliorini, P. J. , Untaroiu, A. , Witt, W. C. , Morgan, N. R. , and Wood, H. G. , 2014, “ Hybrid Analysis of Gas Annular Seals With Energy Equation,” ASME J. Tribol., 136(3), p. 031704. [CrossRef]
Childs, D. W. , Mclean, J. E. , Zhang, M. , and Arthur, S. P. , 2015, “ Rotordynamic Performance of a Negative-Swirl Brake for a Tooth-on-Stator Labyrinth Seal,” ASME J. Eng. Gas Turbines Power, 138(6), p. 062505. [CrossRef]
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Untaroiu, A. , Untaroiu, C. D. , Wood, H. G. , and Allaire, P. E. , 2012, “ Numerical Modeling of Fluid-Induced Rotordynamic Forces in Seals With Large Aspect Ratios,” ASME J. Eng. Gas Turbines Power, 135(1), p. 012501. [CrossRef]
Morgan, N. R. , Wood, H. G. , and Untaroiu, A. , 2015, “ Numerical Optimization of Leakage by Multifactor Regression of Trapezoidal Groove Geometries for a Balance Drum Labyrinth Seal,” ASME Paper No. GT2015-43794.
Migliorini, P. J. , Untaroiu, A. , and Wood, H. G. , 2014, “ A Numerical Study on the Influence of Hole Depth on the Static and Dynamic Performance of Hole-Pattern Seals,” ASME J. Tribol., 137(1), p. 011702. [CrossRef]
Jin, H. X. , and Untaroiu, A. , 2016, “ Elliptical Shape Hole-Pattern Seals Performance Evaluation Using Design of Experiments Technique,” ASME Paper No. FEDSM2016-7687.

Figures

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Fig. 4

Constrained axial direction

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Fig. 5

Constrained circumferential direction

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Fig. 1

Fluid domain of the seal model: (a) overview of the fluid domain and (b) zoom in view of labyrinth seal and swirl brake

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Fig. 11

DOE analysis of leakage rate: (a) Pareto chart and (b) main effect chart

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Fig. 12

DOE analysis of circumferential velocity: (a) Pareto chart and (b) main effect chart

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Fig. 13

DOE analysis of preswirl ratio: (a) Pareto chart and (b) main effect chart

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Fig. 6

A 360-deg fluid domain and sector fluid domain

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Fig. 7

Plots with different meshes for: (a) pressure and (b) average velocity

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Fig. 8

Mesh grid of the 1/36 sector model: (a) overview of the 1/36 sector mesh grid and (b) mesh grid of the grooves

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Fig. 17

High performance model compared to the baseline model, where Vt is the average circumferential velocity

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Fig. 9

Fluid domain setup

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Fig. 10

DOE outputs: (a) locations shown in geometry and (b) locations shown in velocity profile along axial direction for baseline geometry

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Fig. 14

Effective swirl brake length

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Fig. 15

Effective angle: (a) high circumferential velocity and (b) low circumferential velocity

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Fig. 16

Circumferential velocity chart of Swirl brake length/Effective swirl brake length: (a) Swirl brake length and (b) effective swirl brake length

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