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Research Papers: Gas Turbines: Structures and Dynamics

Physical Understanding and Sensitivities of Low Pressure Turbine Flutter

[+] Author and Article Information
Joshua J. Waite

Duke University,
Durham, NC 27708
e-mail: joshua.waite@duke.edu

Robert E. Kielb

Duke University,
Durham, NC 27708
e-mail: rkielb@duke.edu

Contributed by the Structures and Dynamics Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received June 14, 2014; final manuscript received June 29, 2014; published online August 26, 2014. Editor: David Wisler.

J. Eng. Gas Turbines Power 137(1), 012502 (Aug 26, 2014) (9 pages) Paper No: GTP-14-1287; doi: 10.1115/1.4028207 History: Received June 14, 2014; Revised June 29, 2014

Successful, efficient turbine design requires a thorough understanding of the underlying physical phenomena. This paper investigates the flutter phenomenon of low pressure turbine (LPT) blades seen in aircraft engines and power turbines. Computational fluid dynamics (CFD) analysis will be conducted in a two-dimensional (2D) sense using a frequency domain Reynolds-averaged Navier—Stokes (RANS) solver on a publicly available LPT airfoil geometry: École Polytechnique Fédérale De Lausanne (EPFL's) Standard Configuration 4. An emphasis is placed on revealing the underlying physics behind the threatening LPT flutter mechanism. To this end, flutter sensitivity analysis is conducted on three key parameters: reduced frequency, mode shape, and Mach number. Additionally, exact 2D acoustic resonance interblade phase angles (IBPAs) are analytically predicted as a function of reduced frequency. Made evident via damping versus IBPA plots, the CFD model successfully captures the theoretical acoustic resonance predictions. Studies of the decay of unsteady aerodynamic influence coefficients away from a reference blade are also presented. The influence coefficients provide key insights to the harmonic content of the unsteady pressure field. Finally, this work explores methods of normalizing the work per cycle by the exit dynamic pressure.

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References

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Figures

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Fig. 1

TD plot of standard configuration 4: M2 = 0.90. Neighboring blades shown for cascade orientation. ξ and η normalized by chord length. Used with permission [7].

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Fig. 2

Photo of experimental setup for standard configuration 4. (a) 627 (subsonic) and (b) 628 (supersonic).

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Fig. 3

Absolute Mach number distributions. (a) 627 (subsonic exit) and (b) 628 (supersonic exit).

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Fig. 4

2D acoustic resonance conditions for subsonic and supersonic flows. (a) Subsonic exit and (b) supersonic exit.

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Fig. 5

Fundamental mode shapes considered during flutter sensitivity analysis. Displacements exaggerated 5 x for depiction. (a) flex and (b) pitching at leading edge.

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Fig. 6

Damping versus IBPA for subsonic flow case at various reduced frequencies. (a) Flex and (b) pitching at leading edge.

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Fig. 7

Magnitude of the GF influence coefficients for subsonic flow case at various reduced frequencies. (a) Flex and (b) pitching at leading edge.

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Fig. 8

Damping versus IBPA for supersonic flow case at various reduced frequencies. (a) Flex and (b) pitching at leading edge.

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Fig. 9

Magnitude of the GF influence coefficients for supersonic flow case at various reduced frequencies. (a) Flex mode and (b) pitching at leading edge.

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Fig. 10

Amplitude of unsteady pressure field due to reference blade flex vibration only. Subsonic flow, k = 0.1.

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Fig. 11

Amplitude of unsteady pressure field due to only the reference blade pitching about the leading edge. Subsonic flow, k = 0.1.

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Fig. 12

Work-per-cycle versus IBPA for subsonic, transonic, and supersonic flow cases. Pitching about the leading edge, k = 0.1 (a) Without normalization and (b) normalized by qexit1.5.

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