Fundamental Frequencies of Turbine Blades With Geometry Mismatch in Fir-Tree Attachments

[+] Author and Article Information
Fei Qin, Liming Chen

School of Mechanical Engineering and Applied Electronics Technology, Beijing University of Technology, Beijing 100022, P.R.C.

Ying Li

 China Huanqiu Contracting and Engineering Corporation, Beijing 100029, P.R.C.

Xiaofeng Zhang

 China Continuous Casting Technology Engineering Co.Ltd, Beijing 100081, P.R.C.

J. Turbomach 128(3), 512-516 (Feb 06, 2006) (5 pages) doi:10.1115/1.2187523 History: Received September 19, 2005; Revised February 06, 2006

Geometry mismatch in a turbine blade root, which arose in manufacturing process or caused by wearing out during service, leads to contact conditions changed in fir-tree attachments. As a result, shifting of the fundamental frequencies and redistribution of stress in the blade base possibly cause failure of the blade. A three-dimensional finite element model of a blade and its fir-tree attachments have been constructed and analyzed by taking into account contact nonlinearity in the attachments and large deformation effect of the blade. The geometry mismatch was introduced into the finite element model by defining gaps between two contact surfaces in the attachments. The influence of gap configuration and gap size on contact and fundamental frequencies was investigated. Results showed that gap configuration has significant influence on fundamental frequencies of the blade, especially on its bending modes. Gap size has little influence on the frequencies but significant influence on the contact status and thus changes stress distribution in the attachments. The results also suggest that modeling contact behavior in fir-tree attachments is necessary to obtain more accurate fundamental frequencies.

Copyright © 2006 by American Society of Mechanical Engineers
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Figure 1

3-D geometric models of (a) steam turbine blade with fir-tree root and (b) one sector of a disk

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Figure 2

Finite element mesh of the fir-tree attachments, in which fine elements are placed around the contact surfaces

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Figure 3

Sketches of (a) fir-tree attachments and (b) definition of the gap. Some points are tagged as a, b,…,h in order to observe contact status in the attachments.

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Figure 4

Frequency change Δf (in percentage) compared with the zero-gap model



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