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Research Papers: Other (Seals, Manufacturing)

Step Clearance Seals: An Analysis to Demonstrate Their Unique Performance

[+] Author and Article Information
Xueliang Lu

Department of Mechanical Engineering,
Texas A&M University,
College Station, TX 77843
e-mail: luliang413@gmail.com

Luis San Andrés

Mast-Childs Chair Professor
Fellow ASME
Department of Mechanical Engineering,
Texas A&M University,
College Station, TX 77843
e-mail: Lsanandres@tamu.edu

1A dry condition denotes a test facility without water being supplied.

Contributed by the Tribology Division of ASME for publication in the JOURNAL OF TRIBOLOGY. Manuscript received May 23, 2018; final manuscript received October 5, 2018; published online November 21, 2018. Assoc. Editor: Noel Brunetiere.

J. Tribol 141(3), 032203 (Nov 21, 2018) (8 pages) Paper No: TRIB-18-1198; doi: 10.1115/1.4041719 History: Received May 23, 2018; Revised October 05, 2018

Hydraulic turbines and centrifugal pumps at times show low frequency vibrations when installed with upstream step (band) clearance seals with a narrow clearance facing the incoming external flow. When implementing a downstream step clearance seal, one with the narrow clearance located at the seal exit, the same machine does not show the same problem. This paper presents both theoretical and experimental analysis on the leakage and dynamic force coefficients of both upstream and downstream step clearance seals. The predicted and measured results show that an upstream step clearance seal produces a significant negative direct stiffness (K < 0) that could cause a static instability. On the other hand, a downstream step clearance seal generates a positive direct stiffness (K > 0) that is beneficial to a rotor system. Both the upstream and downstream step clearance seals show positive direct damping and virtual mass coefficients.

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References

Childs, D. W. , 1989, “ Fluid-Structure Interaction Forces at Pump-Impeller-Shroud Surfaces for Rotordynamic Calculations,” ASME J. Vib. Acoust., 111(3), pp. 216–315. [CrossRef]
Khakurel, N. , 2015, “ Cavitation in Francis Turbines,” M.S. thesis, Aachen University of Applied Sciences, Aachen, Germany.
Tsujimoto, Y. , Ma, Z. , Song, B. , and Horiguchi, H. , 2010, “ Moment Whirl Due to Leakage Flow in the Back Shroud Clearance of a Rotor,” IJFMS, 3(3), pp. 235–244. [CrossRef]
Song, B. , Horiguchi, H. , Ma, Z. , and Tsujimoto, Y. , 2010, “ Rotordynamic Moment on the Backshroud of a Francis Turbine Runner Under Whirling Motion,” ASME J. Fluids Eng., 132(7), p. 071102. [CrossRef]
Nishimura, H. , Horiguchi, H. , Suzuki, T. , Tsujimoto, Y. , and Sugiyama, K. , 2016, “ Super-Synchronous Self-Excited Vibration of a Cylindrical Rotor Due to Axial Leakage Flow,” 28th IAHR Symposium on Hydraulic Machinery and Systems (IAHR2016), Grenoble, France, July 4–8, p. 072001.
San Andrés, L. , Lu, X. , and Zhu, J. , 2018, “ On the Leakage and Rotordynamic Force Coefficients of Pump Annular Seals Operating With Air/Oil Mixtures: Measurements and Predictions,” Second TAMU Asia Turbomachinery and Pump Symposium, Singapore, Mar. 12–15. https://oaktrust.library.tamu.edu/handle/1969.1/172516
Delgado, A. , and San Andrés, L. , 2007, “ A Model for Improved Prediction of Force Coefficients in Grooved Squeeze Film Dampers and Oil Seal Rings,” ASME J. Tribol., 132(3), p. 032202. [CrossRef]
San Andrés, L. , Yang, J. , and Lu, X. , 2019, “ On the Leakage, Torque, and Dynamic Force Coefficients of Air in Oil (Wet) Annular Seal: A Computational Fluid Dynamics Analysis Anchored to Test Data,” ASME J. Eng. Gas Turbines Power, 141(2), p. 021008. [CrossRef]
San Andrés, L. , and Vance, J. M. , 1987, “ Effect of Fluid Inertia on Squeeze-Film Damper Forces for Small-Amplitude Circular-Centered Motions,” ASLE Trans., 30(1), pp. 63–68. [CrossRef]
San Andrés, L. , 2010, “ Annular Pressure (Damper) Seals,” Modern Lubrication Theory, Notes 12(a), Texas A&M University Digital Libraries, College Station, TX, accessed May 21, 2018, http://oaktrust.library.tamu.Edu/handle/1969.1/93197

Figures

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Fig. 1

Schematic view of a hydraulic turbine [2]

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Fig. 2

Schematic views of two step clearance seals: (a) upstream step clearance seal and (b) downstream step clearance seal

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Fig. 3

Schematic view of an upstream step clearance seal

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Fig. 4

Isometric view of seal test rig [6]

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Fig. 5

Cut view of test seal assembly with lubricant flow path [6]

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Fig. 6

Oil flow rate versus supply pressure for two step clearance seals. Inlet oil temperature 30 °C. Shaft speed 1000 rpm.

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Fig. 7

Direct stiffness (K) versus supply pressure for two step clearance seals. Shaft speed 0–3.5 krpm (ΩR = 23.3 m/s). Inlet oil temperature 30 °C.

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Fig. 8

Cross-coupled stiffness (k) versus supply pressure fortwo step clearance seals. Shaft speed 0–3.5 krpm (ΩR = 23.3m/s). Inlet oil temperature 30 °C. Oil volumetric flow rate 3.4–11.4 L/min.

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Fig. 9

Direct damping (C) versus supply pressure for two step clearance seals. Shaft speed 0–3.5 krpm. Inlet oil temperature (Tin) 30 °C.

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Fig. 10

Direct added mass (M) versus supply pressure for two step clearance seals. Shaft speed 0–3.5 krpm. Inlet oil temperature (Tin) 30 °C.

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Fig. 11

Seal volumetric flow rates (Q) versus length of step clearance (Lstep/L). c1/c2 varies. Shaft speed 3.5 krpm. Inlet oil temperature 30 °C.

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Fig. 12

Direct stiffness (K) versus length of step clearance (Lstep/L). c1/c2 varies. Shaft speed 3.5 krpm. Inlet oil temperature 30 °C.

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Fig. 13

Direct damping coefficient (C) versus length of step clearance (Lstep/L). c1/c2 varies. Shaft speed 3.5 krpm. Inlet oil temperature 30 °C.

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Fig. 14

Seal direct mass (M) versus length of step clearance (Lstep/L). c1/c2 varies. Shaft speed 3.5 krpm. Inlet oil temperature 30 °C. c1/c2 varies.

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