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Research Papers

Effect of the Structural Coupling on the Flutter Onset of a Sector of Low-Pressure Turbine Vanes

[+] Author and Article Information
Ruben Antona1

 School of Aeronautics,  Universidad Politécnica de Madrid, 28040 Madrid, Spain

Roque Corral2

Juan M. Gallardo

Technology and Methods Department,  Industria de TurboPropulsores S.A., 28830 Madrid, Spain

1

Currently at Industria de Turbopropulsores S.A.

2

Also Associate Professor at the Department of Engine Propulsion and Fluid Dynamics of the School of Aeronautics, UPM.

J. Turbomach 134(5), 051007 (May 08, 2012) (8 pages) doi:10.1115/1.4003837 History: Received July 27, 2010; Revised December 15, 2010; Published May 08, 2012; Online May 08, 2012

The effect of the structural coupling in the aeroelastic stability of a packet of low-pressure turbine vanes is studied in detail. The dynamics of a 3D sector vane is reduced to that of a simplified mass-spring model to enhance the understanding of its dynamics and to perform sensitivity studies. It is concluded that the dynamics of the simplified model retains the basic features of the finite element three-dimensional model. A linear fully coupled analysis in the frequency domain of the 3D vane sector has been conducted. It is concluded that the small structural coupling provided by the casing and the inter-stage seal is essential to explain the experimental evidences. It is shown that the use of fully coupled aero/structural methods is necessary to retain the mode interaction that takes place in this type of configurations.

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Copyright © 2012 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Typical geometry and mode shape of an LPT vane packet

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Figure 2

First natural frequencies of an isolated packet of vanes

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Figure 3

Mass-spring model of a packet of vanes with an infinitely stiff platform and no coupling effects

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Figure 4

Scheme of the mechanical coupling mechanisms among the packets and nomenclature of the mass-spring model

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Figure 5

Sketch of a high aspect ratio packet of airfoils, the supporting casing, and the interstage seal

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Figure 6

Dependency of the normalized frequency of the cluster modes with the ISPA

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Figure 7

Nondimensional frequency variation (top), and damping, expressed as a fraction of the critical damping (bottom), associated with the aerodynamic forces obtained by vibrating single airfoils versus the traveling-wave engine order

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Figure 8

Nondimensional frequency correction (left), and critical damping ratio (right) of the cluster and platform dominated modes as a function of the ISPA

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Figure 9

Physical (top) and Fourier (bottom) representation of the aeroelastic modes of a packet of six airfoils with a rigid platform and without inter-packet structural coupling. Left: Pure TW corresponding to the ND = 20. Right: Arbitrary mode composed of different NDs.

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Figure 10

Nondimensional natural frequencies as a function of the nodal diameter and a description of the mode-shapes of the cluster for the simplified calibrated model and no coupling among packets

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Figure 11

Sensitivity to the platform (cp ) and hook (ch ) coupling on the minimum critical damping ratio of the packet using full aero/structural coupling (top) and uncoupled (bottom) approaches

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Figure 12

Aeroelastic eigenvalues of the sector vane retaining (bottom) and not retaining (top) the structural coupling among the sectors for the ND = −5

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Figure 13

Aeroelastic eigenvalues of the sector vane retaining (bottom) and not retaining (top) the structural coupling among the sectors for the ND = +5

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