A Simplified Method for Predicting the Stability of Aerodynamically Excited Turbomachinery

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.