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Research Papers: Gas Turbines: Structures and Dynamics

Eddy Current Damper for Turbine Blading: Electromagnetic Finite Element Analysis and Measurement Results

[+] Author and Article Information
Jacob Laborenz1

Institute of Dynamics and Vibration Research,  Leibniz Universität Hannover, 30167 Hannover, Germanylaborenz@ids.uni-hannover.de

Malte Krack, Lars Panning, Jörg Wallaschek

Institute of Dynamics and Vibration Research,  Leibniz Universität Hannover, 30167 Hannover, Germany

Markus Denk, Pierre-Alain Masserey

ALSTOM Power, Steam Turbines and Generators, 5401 Baden, Switzerland

1

Address all correspondence to this author

J. Eng. Gas Turbines Power 134(4), 042504 (Feb 01, 2012) (8 pages) doi:10.1115/1.4004734 History: Accepted June 21, 2011; Received June 21, 2011; Published February 01, 2012; Online February 01, 2012

In the dynamics of turbomachinery, the mechanical damping of the blading has been the focus of research for the last decades to improve the dynamic performance in terms of high cycle fatigue issues. In addition, an increased mechanical damping can produce a higher flutter safety margin such that stable operation conditions are achievable in a bigger range. Hence, novel damping techniques are considered besides the well known friction based damping devices. In this paper, an extended analysis of the eddy current based damping device for a last stage steam turbine blading presented in GT2009-59593 is conducted. A transient electromagnetic finite element analysis of the eddy current damper is performed, and the resulting damping forces are compared to their analytical solution. Parameter studies are carried out, and equivalent damping factors are calculated. Furthermore, for the validation of the finite element model, a test rig was built that allows for the direct measurement of damping forces when forcing a sinusoidal relative motion. Forced response measurements and simulations are used to demonstrate its dynamic performance and predictability.

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic sketch of damping element consisting of permanent magnets and copper plates

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Figure 2

2D axially symmetric finite element model consisting of magnets, copper plates, moving region, band and ballon boundary

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Figure 3

Finite element mesh after fourth iteration (not final); left: full region; right: detail

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Figure 4

Force convergence

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Figure 5

Eddy current distribution with respect to radial position (midplane of the copper plate) at Δz = a for velocities υ(ωt = π/2) = υ0 and υ(ωt = 3π/2) = −υ0

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Figure 6

Transient forces of copper plate (squares), magnet (diamonds) and resulting force (circles) in time and frequency domain; a = 4 mm, β = 0.85, f = 200 Hz

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Figure 7

Finite element based (solid) and analytical (dashed) equivalent damping constant deqv and stiffness ceqv versus air gap a and amplitude ratio β; f = 200 Hz

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Figure 8

Test rig for the direct measurement of damping forces consisting of damping element vibration exciter to force sinusoidal motion and measurement devices

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Figure 9

Static force between magnets with respect to air gap

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Figure 10

One period of measured and simulated force in time and frequency domain; a = 4 mm, β = 0.6, f = 50 Hz

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Figure 11

Comparison of measured (stems) and simulated (FEA, surface) equivalent damping constant and stiffness; f = 50 Hz

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Figure 12

Test rig for forced response analyses consisting of dummy blade pair with damping element vibration exciter and vibrometer (not shown)

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Figure 13

Forced response measurements (solid curve) and simulations (dotted-dashed curve) for different air gaps a

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