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Technical Briefs

Guided Tuning of Turbine Blades: A Practical Method to Avoid Operating at Resonance

[+] Author and Article Information
Loc Duong

Principal Engineer
Hamilton Sundstrand Power Systems,
San Diego, CA 92186
e-mail: loc.duong@hs.utc.com

Kevin D. Murphy

Professor
email: kdm@engr.uconn.edu

Kazem Kazerounian

Professor
e-mail: kazem@engr.uconn.edu
University of Connecticut,
Storrs, CT 06269

1Corresponding author.

Contributed by the Design Engineering Division of ASME for publication in the JOURNAL OF VIBRATION AND ACOUSTICS. Manuscript received April 30, 2012; final manuscript received May 14, 2013; published online June 19, 2013. Assoc. Editor: Yukio Ishida.

J. Vib. Acoust 135(5), 054502 (Jun 19, 2013) (5 pages) Paper No: VIB-12-1129; doi: 10.1115/1.4024761 History: Received April 30, 2012; Revised May 14, 2013

In gas turbine applications, forced vibrations of turbine blades under resonant—or nearly resonant—conditions are undesirable. Usually in airfoil design procedures, at least the first three blade modes are required to be free of excitation in the operating speed range. However, not uncommonly, a blade may experience resonance at other higher natural frequencies. In an attempt to avoid resonant oscillations, the structural frequencies are tuned away from the excitation frequencies by changing the geometry of the blade. The typical iterative design process—of adding and removing material through restacking the airfoil sections—is laborious and in no way assures an optimal design. In response to the need for an effective and fast methodology, the guided tuning of turbine blades method (GTTB) is developed and presented in this paper. A practical tuning technique, the GTTB method is based on structural perturbations to the mass and stiffness at critical locations, as determined by the methodology described herein. This shifts the excited natural frequency out of the operating speed range, while leaving the other structural frequencies largely undisturbed. The methodology is demonstrated here in the redesign of an actual turbine blade. The numerical results are experimentally validated using a laser vibrometer. The results indicate that the proposed method is not computationally intensive and renders effective results that jibe with experiments.

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References

Figures

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Fig. 1

The effects of blade tuning in the Campbell diagram

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Fig. 3

The trailing edge of the blade with subvolumes at the primary modal peak

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Fig. 4

Percent of the frequency shift as a function of material volume removal at the primary modal peak. The model predictions and experimental results are both shown.

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Fig. 5

The test configuration, including the laser vibrometer, shaker table, support fixture, and blade

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Fig. 6

(a) Measured mode shape of the baseline blade at point A in the Campbell diagram. (b) The mode shape of the tuned blade after the second iteration (with a 5.5% change in the frequency).

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