In the late 1970s, Benckert and Wachter (Technical University Stuttgart) tested labyrinth seals using air as the test media and measured direct and cross-coupled stiffness coefficients. They reported the following results: (1) fluid preswirl in the direction of shaft rotation creates destabilizing cross-coupled stiffness coefficients and (2) effective swirl brakes at the inlet to the seal can markedly reduce the cross-coupled stiffness coefficients, in many cases reducing them to zero. In recent years, “negative-swirl” swirl brakes have been employed, which attempt to reverse the circumferential direction of inlet flow, changing the sign of the cross-coupled stiffness coefficients and creating stabilizing stiffness forces. This study presents test results for a 16-tooth labyrinth seal with positive inlet preswirl (in the direction of shaft rotation) for the following inlet conditions: (1) no swirl brakes, (2) straight, conventional swirl brakes, and (3) negative-swirl swirl brakes. The negative-swirl swirl-brake designs were developed based on computational fluid dynamics (CFD) predictions. Tests were conducted at 10.2, 15.35, and 20.2 krpm with 70 bar of inlet pressure for pressure ratios of 0.3, 0.4, and 0.5. Test results include leakage and rotordynamic coefficients. In terms of leakage, the negative-swirl brake configuration leaked the least, followed by the conventional brake, followed by the no-brake design. Normalized to the negative-swirl brake configuration, the conventional-brake and no-brake configurations mass flow rate was greater, respectively, by factors of 1.04 and 1.09. The direct-stiffness coefficients are negative but small, consistent with past experience. The conventional swirl brake drops the destabilizing cross-coupled stiffness coefficients k by a factor of about 0.8 as compared to the no-brake results. The negative-swirl brake produces a change in sign of k with an appreciable magnitude; hence, the stability of forward precessing modes would be enhanced. In descending order, the direct-damping coefficients C are: no-swirl, negative-swirl, and conventional-swirl. Normalized in terms of the no-swirl case, C for the negative and conventional brake designs is, respectively, 0.7 and 0.6 smaller. The effective damping Ceff combines the effect of k and C. Ceff is large and positive for the negative-swirl configuration and near zero for the no-brake and conventional-brake designs. The present results for a negative-brake design are very encouraging for both eye-packing seals (where conventional swirl brakes have been previously employed) and division-wall and balance-piston seals, where negative shunt injection has been employed.
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June 2016
Research-Article
Rotordynamic Performance of a Negative-Swirl Brake for a Tooth-on-Stator Labyrinth Seal
Dara W. Childs,
Dara W. Childs
Turbomachinery Laboratory,
The Leland T. Jordan Chair
of Mechanical Engineering,
Texas A&M University,
College Station, TX 77843
e-mail: dchilds@tamu.edu
The Leland T. Jordan Chair
of Mechanical Engineering,
Texas A&M University,
College Station, TX 77843
e-mail: dchilds@tamu.edu
Search for other works by this author on:
James E. Mclean, Jr.,
James E. Mclean, Jr.
Turbomachinery Laboratory,
Texas A&M University,
College Station, TX 77843
Texas A&M University,
College Station, TX 77843
Search for other works by this author on:
Min Zhang,
Min Zhang
Turbomachinery Laboratory,
Texas A&M University,
College Station, TX 77843
Texas A&M University,
College Station, TX 77843
Search for other works by this author on:
Stephen P. Arthur
Stephen P. Arthur
Search for other works by this author on:
Dara W. Childs
Turbomachinery Laboratory,
The Leland T. Jordan Chair
of Mechanical Engineering,
Texas A&M University,
College Station, TX 77843
e-mail: dchilds@tamu.edu
The Leland T. Jordan Chair
of Mechanical Engineering,
Texas A&M University,
College Station, TX 77843
e-mail: dchilds@tamu.edu
James E. Mclean, Jr.
Turbomachinery Laboratory,
Texas A&M University,
College Station, TX 77843
Texas A&M University,
College Station, TX 77843
Min Zhang
Turbomachinery Laboratory,
Texas A&M University,
College Station, TX 77843
Texas A&M University,
College Station, TX 77843
Stephen P. Arthur
Contributed by the Structures and Dynamics Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received September 28, 2015; final manuscript received October 13, 2015; published online November 24, 2015. Editor: David Wisler.
J. Eng. Gas Turbines Power. Jun 2016, 138(6): 062505 (8 pages)
Published Online: November 24, 2015
Article history
Received:
September 28, 2015
Revised:
October 13, 2015
Citation
Childs, D. W., Mclean, J. E., , Jr., Zhang, M., and Arthur, S. P. (November 24, 2015). "Rotordynamic Performance of a Negative-Swirl Brake for a Tooth-on-Stator Labyrinth Seal." ASME. J. Eng. Gas Turbines Power. June 2016; 138(6): 062505. https://doi.org/10.1115/1.4031877
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