A Simplified Method for Predicting the Stability of Aerodynamically Excited Turbomachinery

[+] Author and Article Information
Albert F. Storace

Consulting Engineer Dynamics, Advanced Technology and Preliminary Design, GE Aviation, Cincinnati, OH

J. Turbomach 129(4), 724-729 (Aug 29, 2006) (6 pages) doi:10.1115/1.2720870 History: Received August 11, 2006; Revised August 29, 2006

A modal stability (MS) method is presented for the quick and accurate prediction of the stability of aerodynamically excited turbomachinery using real eigenvalue/eigenvector data obtained from a rotordynamics model. The modal stability method provides a means to compare the work of stabilizing damping forces to the work of destabilizing aerodynamic cross-coupled stiffness forces to predict the onset of whirl instability. The MS method thus indicates that unstable or self-excited whirling (sometimes called whipping) at one of the system’s natural frequencies is initiated when the destabilizing work equals or exceeds the stabilizing work. This approach provides a powerful design tool to quickly ascertain the effects of squeeze-film dampers, and turbine engine architecture, including bearing locations and bearing support structure stiffness, on system stability.

Copyright © 2007 by American Society of Mechanical Engineers
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Grahic Jump Location
Figure 1

Cross-coupled stiffness forces acting on the rotor and stator (forward whirl direction is counterclockwise-forward looking aft (FLA))

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Figure 2

Structural network for turbine engine rotordynamics model

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Figure 3

Squeeze-film damper+squirrel cage component Q factor as a function of damper radial clearance and land length

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Figure 4

Modal stability criterion (MSC) value as a function of squeeze-film damper+centering spring component Q-factor (damper geometry dependency)



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