TECHNICAL PAPERS: Gas Turbines: Structures and Dynamics

Sensitivity of Tuned Bladed Disk Response to Frequency Veering

[+] Author and Article Information
J. A. Kenyon

 Air Force Research Laboratory, Propulsion Directorate, Wright-Patterson AFB, OH 45433james.kenyon@wpafb.af.mil

J. H. Griffin

Department of Mechanical Engineering,  Carnegie Mellon University, Pittsburgh, PA 15213jg9h@Andrew.cmu.edu

N. E. Kim

 Hood Technologies, Hood River, OR 97031nek@hoodtach.com

In the gas turbine industry the term “nodal diameter” is commonly used to indicate the phase angle of the cyclic symmetric constraint applied in a single sector finite element analysis used to calculate the natural frequencies and mode shapes of the bladed disk. It is understood that the actual number of nodal diameters is often larger than this because of nodal diameters within the sector model, e.g., torsion modes have at least one nodal diameter per blade.

J. Eng. Gas Turbines Power 127(4), 835-842 (Mar 01, 2004) (8 pages) doi:10.1115/1.1924486 History: Received October 01, 2003; Revised March 01, 2004

A continuous method is presented for representing the mode interaction that occurs in frequency veering in terms of the nominal sector modes of a cyclic symmetric bladed disk model constrained at a reference interblade phase angle. Using this method, the effect of frequency veering on the mode shapes can be considered in the context of the generalized forces exciting the system and the modal response of the bladed disk. It is shown that in a blade-dominated family of modes, the transfer of modal energy to the disk in the veering results in a lower generalized force exciting the mode as well as reduced response amplitude in the blade. For the disk-dominated modes, the sharing of modal energy with the blades can lead to the disk being excited by aerodynamic loading. These effects can have important implications for predicting and interpreting forced response in bladed disks. Numerical examples are provided to illustrate these concepts.

Copyright © 2005 by American Society of Mechanical Engineers
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Figure 8

Bladed disk natural frequencies with veering between blade and seal modes

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Figure 1

Lumped parameter model of bladed disk dynamics

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Figure 2

Natural frequencies of the lumped parameter system

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Figure 3

Mode shape exchange in frequency veering

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Figure 4

Effects of frequency veering on generalized forces

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Figure 5

Effect of frequency veering on blade modal response, baseline, and perturbed system with disk stiffness change

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Figure 6

Increase in forced response amplitude due to a perturbation in tuned system properties

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Figure 7

Finite element model of a fan rotor with a knife-edge seal

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Figure 9

Changes in veering behavior due to changes in seal stiffness–thickness

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Figure 10

Projection of finite element model modes onto seal mode at 5 nodal diameters

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Figure 11

Effect of frequency veering proximity on seal stress



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