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Research Papers

An Aerodynamic Parameter for Low-Pressure Turbine Flutter

[+] Author and Article Information
Fernando Barbarossa

Vibration UTC,
Department of Mechanical Engineering,
Imperial College London,
London SW7 2BX, UK
e-mail: fernando.barbarossa12@imperial.ac.uk

Anthony B. Parry

Rolls Royce plc,
Derby DE248BJ, UK
e-mail: anthony.parry@rolls-royce.com

Jeffrey S. Green

Rolls Royce plc,
Derby DE248BJ, UK
e-mail: jeffrey.green@rolls-royce.com

Luca di Mare

Vibration UTC,
Department of Mechanical Engineering,
Imperial College London,
London SW7 2BX, UK
e-mail: l.di.mare@imperial.ac.uk

1Corresponding author.

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received February 23, 2015; final manuscript received September 7, 2015; published online January 12, 2016. Assoc. Editor: Rakesh Srivastava.

J. Turbomach 138(5), 051001 (Jan 12, 2016) (11 pages) Paper No: TURBO-15-1028; doi: 10.1115/1.4032184 History: Received February 23, 2015; Revised September 07, 2015

This paper presents a study on low-pressure (LP) turbine bending flutter. The study is performed using a semi-analytical model, which is validated against experimental and computational fluid dynamics (CFD) data. The validation highlights the ability of even the simplest models to represent accurately the flutter behavior of the LP turbine assemblies. A parametric study is then performed into the effect of modifications of the blade camber line on the stability of bending modes. Variations in maximum camber position, leading edge and trailing edge metal angles, and stagger are considered. The modifications are applied to a family of aerodynamically well designed aerofoils and to a family of aerodynamically poorly designed aerofoils. Trends relating damping to the parameters describing the camber line modifications are identified. These trends are found to apply to both families of aerofoils. Furthermore, it is found that the behavior of all aerofoils studied can be characterized by their behavior at a specific flow angle and by a simple algebraic relation based on true incidence. This behavior also seems to be universal.

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References

Figures

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Fig. 2

First standard configuration. (a) Variation of damping parameter with Φ. (b)–(d) Amplitude of unsteady pressure coefficients at Φ=−180 deg, Φ=−90 deg, and Φ=−45 deg, respectively.

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Fig. 3

Fourth standard configuration. (a) Damping parameter versus Φ. Unsteady pressure coefficients at (b) Φ=−90 deg and (c) Φ=90 deg.

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Fig. 4

Damping coefficient versus Φ—Left: bending mode and right: interlock configuration

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Fig. 5

Aerofoil leading edge modifications. (a) Position of maximum camber, (b) leading edge metal angle, (c) trailing edge metal angle, and (d) re-stagger.

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Fig. 6

Flow and metal angles

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Fig. 7

Cp at i* = 0 for (a) well-designed cascade and (b) poorly designed cascade

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Fig. 8

Flow field past a cascade at α=α*

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Fig. 9

Effect of camber line modifications on modal force at i*=0. (a) Top: maximum camber, bottom: leading-edge metal angle. (b) Top: trailing-edge metal angle, bottom: stagger. Left: well-designed aerofoils, right: poorly designed aerofoils.

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Fig. 10

Effect of camber line modifications on unsteady pressure coefficients at i*=0. The coefficients shown refer to Φ=−90, which corresponds to the minimum damping. (a) Top: maximum camber, bottom: leading-edge metal angle. (b) Top: trailing-edge metal angle, bottom: stagger. Left: well-designed aerofoils and right: poorly designed aerofoils.

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Fig. 11

Effect of camber line modifications on the damping of the least damped mode. (a) Top: maximum camber and bottom: leading-edge metal angle. (b) Top: trailing-edge metal angle and bottom: stagger. Left: well designed aerofoils and right: poorly designed aerofoils.

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Fig. 12

Parabolic variation of minimum damping with camber line geometry. (a) Maximum camber, (b) leading-edge metal angle, (c) trailing-edge metal angle, and (d) stagger.

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