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TECHNICAL PAPERS: Gas Turbines: Structures and Dynamics

Characterization of Turbine Blade Friction Dampers

[+] Author and Article Information
K.-H. Koh, J. H. Griffin, A. Akay

Department of Mechanical Engineering,  Carnegie Mellon University, Pittsburgh, PA 15213

S. Filippi1

Department of Mechanical Engineering,  Carnegie Mellon University, Pittsburgh, PA 15213

Note that we had to periodically measure $μ$ and take its change into account in developing the dimensionless damping and stiffness curves quoted in this paper.

1

On leave from Politecnico di Torino, Turin, Italy.

J. Eng. Gas Turbines Power 127(4), 856-862 (Mar 01, 2004) (7 pages) doi:10.1115/1.1926312 History: Received October 01, 2003; Revised March 01, 2004

Abstract

This paper discusses an approach for characterizing the dynamic behavior of a friction damper. To accomplish this, the deflection of the damper is measured as a function of an applied force for a range of amplitudes, normal loads, and excitation frequencies. The resulting hysteresis curves are used to generate curves of nonlinear stiffness and damping as a function of the amplitude of motion. A method of presenting this information in a dimensionless format is demonstrated. This format allows direct comparisons of the nonlinear stiffness and damping of actual dampers with that often used in analytical models to compute the dynamic response of frictionally damped turbine blades. It is shown that for the case of a damper with a spherical head significant differences exist between the actual behavior of the damper and that often assumed in simple analytical models. In addition, Mindlin’s analysis of a sphere on a half space is used to estimate the damper’s stiffness as well as its theoretical hysteresis curves. The hysteresis curves are then used to determine dimensionless stiffness and damping curves. The results compare favorably with those found experimentally.

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Figures

Figure 1

Spring damper element

Figure 2

Hysteresis from spring damper element

Figure 3

Nondimensional effective stiffness

Figure 4

Nondimensionalized effective damping

Figure 5

Experimental setup for quasi-static test

Figure 6

Friction damper specimen for quasi-static test

Figure 7

Experimental setup for dynamic test

Figure 8

Hysteresis curves from quasi-static tests

Figure 9

Hysteresis curves from dynamic tests

Figure 10

Calculating damper stiffness from the hysteresis

Figure 11

Experimentally generated curves compared with benchmark

Figure 12

Friction contact of sphere on a flat surface

Figure 13

Relative displacement between two bodies in contact (F<μN)

Figure 14

Hysteresis from Mindlin analysis

Figure 15

Comparison between experiments and Mindlin analysis

Figure 16

Dimensionless hysteresis loop from Mindlin theory

Figure 17

Design range in damper optimization curve

Figure 18

Design range in effective damping curve

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