Abstract
In order to evaluate the rotor stability of a high pressure compressor, the forward eigen modes need to be distinguished
from the backward eigen modes, and the frequencies and the damping ratios need also to be identified with a good accuracy.
In this paper, a complex expression is introduced for the rotor motion and a directional frequency response functions that
enable the separation of those modes in the frequency domain is derived. Curve fitting is also introduced for the frequency
response functions to determine the frequencies and damping ratios based on system identification methods, such as prediction
error methods. These techniques were applied to a stability evaluation for the low pressure gas operation, in which condition
the stability mainly depends on the bearing property. Finally, the bearing coefficients are estimated by using an optimization
method.
