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The Measurement of Dynamic Vibration Modes and Frequencies of a Large LP Bladed Disc

[+] Author Affiliations
Lubos Prchlik, Tomas Misek, Zdenek Kubin, Karel Duchek

Skoda Power, Plzen, Czech Republic

Paper No. GT2009-60002, pp. 447-453; 7 pages
doi:10.1115/GT2009-60002
From:
  • ASME Turbo Expo 2009: Power for Land, Sea, and Air
  • Volume 6: Structures and Dynamics, Parts A and B
  • Orlando, Florida, USA, June 8–12, 2009
  • Conference Sponsors: International Gas Turbine Institute
  • ISBN: 978-0-7918-4887-6 | eISBN: 978-0-7918-3849-5
  • Copyright © 2009 by ASME

abstract

A new 48″ steam turbine last stage blade (LSB) has been developed by the common effort of Skoda Power and Ansaldo Energia. The successful detuning of eigen-frequencies with respect to the basic rotational frequency has been achieved by using interconnecting elements near the mid-span and at the shroud of blades. Friction forces among the contact elements resulted from the constraint blade untwist generated by the centrifugal-force. FEM calculation of the Campbell and interference diagrams was followed by a detailed measurement in a specialized vacuum testing rig with strain gages located near the blade root. The excitation was performed by a high-power variable-frequency magnet. For the critical 0-node “umbrella” shape frequency both the axial magnetic excitation and the direct torsional excitation with AC driving motor were applied. Nearly forty different bladed-disc frequencies grouped into five families were identified by the FFT analysis. The corresponding modal shapes were indentified from the relationship between the excitation and resonance frequencies using the time offset of the signal from strain gages distributed along the disc perimeter. An excellent agreement between calculated and measured frequencies and nodal shapes was observed. A typical difference between the predicted and actually measured critical frequencies did not exceed 3% of the nominal value for the relevant frequencies. A complementary measurement using tip-timing technique is currently underway.

Copyright © 2009 by ASME
Topics: Vibration , Disks

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