VIBRATION DAMPER SEALS FOR TURBOMACHINERY

The Pocket Damper Seal (PDS) was invented at Texas A&M University (TAMU) by Dr. John Vance and Richard Shultz. The University holds the patent. It is licensed by Bearings Plus under the trade name “TAMSEAL”. This non-contacting seal has orders of magnitude more direct damping than conventional labyrinth seals, and no de-stabilizing cross-coupled stiffness. It has been used to suppress rotordynamic instability in a number of large multistage high-pressure centrifugal compressors. In most of these machines the critical frequency to suppress is between 3200 and 6000 cpm, and the PDS has maximum damping in that frequency range. The latest design configuration of the TAMSEALTM can produce either positive or negative stiffness, to tune the natural frequency of the machine as desired.

High-pressure (up to 1000 psi) tests of PDS were recently carried out by Dr. Bugra Ertas at speeds up to 20,000 rpm with excitation frequencies 0-300 Hz. Effective damping coefficients are measured to be larger than any other type of non-contacting seal in the frequency range of 40-100 Hz. Dr. Ahmed Gamal continued the research to measure leakage as a function of blade profile and blade pitch. Increased blade pitch was shown to reduce the leakage, so that fewer teeth can be used in a given seal length, which increases the damping. Eccentricity (shaft off center) was shown to produce a smaller increase in leakage for the TAMSEALTM as compared to a labyrinth seal.

 

References

1.      Childs, D.W. and Vance, J.M., Short Course on “Annular Gas Seals and Rotordynamics”, 36th Turbomachinery Symposium, Texas A&M University, September 10-13, 2007.

2.      Ertas, B., and Vance, J.M., “Rotordynamic Force Coefficients for a New Pocket Damper Seal Design”, IFToMM 7th International Conference on Rotor Dynamics, Vienna, Austria, September 25-28, 2006, and ASME Journal of Tribology, Vol. 129,  April 2007, pp. 365-374.

3.      Ertas, B., and Vance, J.M., “The Influence Of Same-Sign Cross-Coupled Stiffness On Rotordynamics”, DETC2005-84873, Proceedings of the ASME Design Engineering and Technical Conference, Long Beach, CA, September 24-28, 2005, and the Journal of Vibrations and Acoustics, 2007.

4.      Shultz, R.M., Analytical and Experimental Investigations of a Labyrinth Seal Test Rig and Damper Seals for Turbomachinery, Master of Science Thesis in Mechanical Engineering, 1997, Texas A&M University.

5.      Li, J., Kushner, F., and De Choudhury, P., “Experimental Evaluation of Slotted gas Pocket Damper Seals On A Rotating Test Rig”, GT-2002-30634. Proceedings of ASME Turbo Expo 2002, Amsterdam, The Netherlands.

6.      Ertas, B.H., Gamal, A. and Vance, J.M., “Rotordynamic Force Coefficients of Pocket Damper Seals”, ASME Journal of Turbomachinery, October 2006, pp. 725 – 737.

7.      Richards, B., Vance, J.M., Paquette, D.J., and Zeidan, F.Y., “Using a Damper Seal to Eliminate Sub-synchronous Vibrations in Three Back to Back Compressors”,  Proceedings of the 24th Turbomachinery Symposium, Houston, Texas, September 26-28, 1995, pp. 59-71.

8.      Li, J., Choudhury, P., and Tacques, R., “Seal And Bearing Upgrade For Eliminating Rotor Instability Vibration In A High Pressure Natural Gas Compressor”, ASME Paper No. GT-2002-30635, Proceedings of ASME Turbo Expo 2002, June 3-6, 2002, Amsterdam, The Netherlands.

9.      Gamal, A.M., Ertas, B.H., and Vance, J.M. “High-Pressure Pocket Damper Seals: Leakage Rates And Cavity Pressures”, Proceedings of GT2006 ASME Turbo Expo 2006: Power for Land, Sea and Air, May 8-11, 2006, Barcelona, Spain.

10.  Gamal, A.M., and Vance, J.M., “Labyrinth Seal Leakage Tests: Tooth Profile, Tooth Thickness, And Eccentricity Effects”, Proceedings of GT2007 ASME Turbo Expo 2007: Power for Land, Sea and Air, May 14-17, 2007, Montreal, Canada.