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Research Papers: Gas Turbines: Structures and Dynamics

Experimental Study on Impeller Blade Vibration During Resonance—Part II: Blade Damping

[+] Author and Article Information
Albert Kammerer, Reza S. Abhari

LEC, Laboratory of Energy Conversion, Department of Mechanical and Process Engineering,  ETH Zurich, 8092 Zürich, Switzerland

J. Eng. Gas Turbines Power 131(2), 022509 (Dec 29, 2008) (9 pages) doi:10.1115/1.2968870 History: Received April 08, 2008; Revised April 08, 2008; Published December 29, 2008

Forming the second part of a two-part paper, the estimation of damping is presented here. Part I discusses the experimental approach and the results on blade resonant response measurements. In the study of forced response, damping is a crucial parameter, which is measured to quantify the ability of a vibrating system to dissipate vibratory energy in response to a given excitation source. The blading of turbomachinery components is particularly prone to forced response excitation, which is one of the major causes of high cycle fatigue failure during operation. In turbocharging applications, forced response cannot be avoided due to a number of factors, i.e., change in speed, inlet bends, or obstructions in the flow field. This study aims to quantify the damping parameter for the lightly damped blades of a centrifugal compressor. The impeller geometry is typical of turbocharging applications. As a first step, the nonrotating impeller was excited using piezos, and the transfer function was derived for a number of pressure settings. Both circle-fit and curve-fit procedures were used to derive material damping. In the second step, measurements were taken in the test facility where forced response conditions were generated using distortion screens upstream of the impeller. The main blade strain response was measured by sweeping through a number of resonant points. A curve-fit procedure was applied to estimate the critical damping ratio. The contributions of material and aerodynamic dampings were derived from a linear curve-fit applied to the damping data as a function of inlet pressure. Overall, it will be shown that aerodynamic damping dominates the dissipation process for applications with an inlet pressure of 1 bar. Damping was found to depend on the throttle setting of the compressor, and where applicable computational fluid dynamics results were used to point toward the possible causes of this effect.

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Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 1

Impeller performance map and Campbell diagram. (a) Compressor map and operating lines. (b) Typical response of the main blade without a distortion screen installed upstream of the impeller.

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Figure 2

Full range response spectrum with piezoelectric excitation

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Figure 3

Examples for amplitude fitting: ((a)–(c)) Mode 1 and ((d)–(f)) Mode 2. (a) Blade No. 1, (b) Blade No. 2, (c) Blade No. 3, (d) Blade No. 1, (e), Blade No. 2, and (f) Blade No. 3.

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Figure 4

Circle-fit method for damping estimation

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Figure 5

Deviation in damping estimation, %(ζcurve−ζcircle)

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Figure 6

Response comparison at 0.1 bar inlet pressure

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Figure 7

Estimated damping for Modes 1 and 2 using piezoelectric excitation

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Figure 8

Mode 1 response from EO5 excitation using a five lobe screen

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Figure 9

Mode 1 response variation depending on inlet pressure

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Figure 10

Damping estimates for Mode 1 and EO5 excitation

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Figure 11

First harmonic amplitude and phase for five lobe excitation obtained from CFD

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Figure 12

Mode 1 response from EO6 excitation using a three lobe screen

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Figure 13

Damping estimates for Mode 1 and EO6 excitation

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Figure 14

Strain response and damping estimates for Mode 2: (a) Mode 2 response from EO12 excitation using a four lobe screen, (b) Mode 2 response from EO10 excitation using a five lobe screen, (c) damping estimates for Mode 2 and EO12 excitation, and (d) damping estimates for Mode 2 and EO10 excitation

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