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Technical Briefs

The Influence of a Cracked Blade on Rotor’s Free Vibration

[+] Author and Article Information
Yi-Jui Chiu

Department of Mechanical Engineering, National Taiwan University of Science and Technology, 43 Kee-Lung Road, Section 4, Taipei 106, Taiwan, R.O.C.

Shyh-Chin Huang

Department of Mechanical Engineering, National Taiwan University of Science and Technology, 43 Kee-Lung Road, Section 4, Taipei 106, Taiwan, R.O.C.schuang@mail.ntust.edu.tw

J. Vib. Acoust 130(5), 054502 (Aug 12, 2008) (8 pages) doi:10.1115/1.2948381 History: Received January 10, 2007; Revised December 14, 2007; Published August 12, 2008

The influence on the coupled vibrations among shaft, disk, and blades of a rotor system due to a cracked blade was investigated analytically. On the shaft-disk-blade system, without a cracked blade, there exist three types of coupled modes, shaft disk blade (SDB), disk blade (DB), and blade-blade. A cracked blade was found to change not only the natural frequencies but also the types of coupled modes. First, the DB modes disappeared and were replaced by SDB modes. Second, in some modes the disk experienced mode localization due to the cracked blade. Numerical results showed that natural frequencies varied with the blade’s crack location and depth. At no bending moment places the crack imposed no effect. The crack affected the natural frequency slightly until its depth reached as deep as 70% then the frequency dropped abruptly.

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Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 8

The 1a and 2a mode frequency variations with crack depth ratio for a five-blade rotor

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Figure 7

The 1a and 2a mode frequency variations with crack location for a five-blade rotor

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Figure 6

Frequency changes due to a cracked blade in a five- and a six-blade rotor (Ω=0) ○ ● Blades’s first mode predominates △ ▲ Blades’s second mode predominates ◇ ◆ Shaft’s torsional mode predominates

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Figure 5

The first five modes of a five-blade rotor with a cracked blade (Ω=0)

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Figure 4

The first five modes of the noncracked five-blade rotor (Ω=0)

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Figure 3

Coordinate sets and deformation of a blade

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Figure 2

The geometry and coordinates of the rotating disk

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Figure 1

(a) A SDB rotor with a cracked (asterisked) blade, (b) definition for stagger angle, and (c) coordinates for the cracked blade

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