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Research Papers: Gas Turbines: Structures and Dynamics

Impulse Mistuning of Blades and Vanes

[+] Author and Article Information
Andreas Hartung

MTU Aero Engines AG,
Munich 80995, Germany
e-mail: andreas.hartung@mtu.de

Ulrich Retze

MTU Aero Engines AG,
Munich 80995, Germany
e-mail: Ulrich.retze@mtu.de

Hans-Peter Hackenberg

MTU Aero Engines AG,
Munich 80995, Germany
e-mail: hans-peter.hackenberg@mtu.de

Contributed by the Structures and Dynamics Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received September 15, 2016; final manuscript received November 21, 2016; published online February 14, 2017. Editor: David Wisler.

J. Eng. Gas Turbines Power 139(7), 072502 (Feb 14, 2017) (9 pages) Paper No: GTP-16-1451; doi: 10.1115/1.4035594 History: Received September 15, 2016; Revised November 21, 2016

Impulse mistuning is an alternative approach for the reduction of vibration stresses of blades and vanes. In contrast to most other approaches, it is not a direct energy dissipation approach but a mistuning based one. However, the approach is not aimed at making use of the geometrical mistuning of the structure (e.g., a blade or a vane stage). Mistuners, specially designed small bodies are placed at specific locations inside of the component, e.g., of a blade or of a vane. They do not directly dissipate enough energy to cause relevant damping like a friction or friction-impact damper, because of the small mass involved, but rather mistune the eigen frequencies of the structure using impulses (impacts). As a result, the structure absorbs less energy at the original resonance and hence answers with lower vibration amplitude. In fact, impulse mistuning is a special case of absorption—the so-called targeted energy transfer (TET) with “vibro-impact nonlinear energy sinks” (VI-NES)—with very small impact mass involved, and thus, a negligible role of dissipation while experiencing a significant amount of absorption. The energy will be transferred (or “pumped”) to other resonances, sometimes outside of the primary resonance crossing and partially dissipated. We use the names “impulse mistuning” or “mistuners” instead of TET or VI-NES because (in our opinion) it better describes the physics of this special kind of absorption. In the paper, the design and validation of two impulse mistuning systems, for a blade stage and a vane cluster of a lower power turbine, are presented.

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References

Figures

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Fig. 1

Lumped-parameter model from Ref. [8] with a free moving damper in a cavity

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Fig. 2

Lumped-parameter model from Ref. [8] with a spring loaded damper in a cavity

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Fig. 3

Forced response for the model shown in Fig. 1, with and without a free damper (0.1 g)

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Fig. 4

Forced response for the model shown in Fig. 1, with and without a free damper (0.8 g)

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Fig. 5

Forced response for the models shown in Figs. 1 and 2, with and without damper (0.5 g)

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Fig. 7

Studies of the model shown in Fig. 6 for the damper masses md1… md7, e=0.7 and two different gaps of damper to cavity wall: (a) l1 and (b) l2

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Fig. 8

Studies of the model shown in Fig. 6 for the damper masses md1… md4, e=1.0 and two different gaps of damper to cavity wall: (a) l2 and (b) l1

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Fig. 9

Vane cluster and damper investigated in Ref. [10]

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Fig. 10

Steady-state solution from Ref. [10] in the form of a SMR

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Fig. 11

Analytical prediction of damping (Fig. 9) using abaqus

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Fig. 12

Experimental confirmation of the predicted damping, (Fig. 9; red curve compares with Fig. 11) [10]

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Fig. 13

Analyzed and tested mode shapes of the blade stage

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Fig. 14

Analytical predictions of the damping effectiveness and robustness of the vane stage impulse mistuning system

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Fig. 15

Analytical prediction of the damping effectiveness of the impulse mistuning system developed for the blade, one of the mode shapes

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Fig. 16

Comparison of the resonance solution with and almost without friction; analytical prediction of the impulse mistuning system, developed for the blade stage

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Fig. 17

Basic functionality of excitation rig

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Fig. 19

Excitation rig measurements and analytical prediction for one of the mode shapes of the blade stage

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