Stability Increase of Aerodynamically Unstable Rotors Using Intentional Mistuning

Abstract

A new simple asymptotic mistuning model, which constitutes an extension of the well known fundamental mistuning model for groups of modes belonging to a modal family exhibiting a large variation of the tuned vibration characteristics, is used to analyze the effect of mistuning on the stability properties of aerodynamically unstable rotors. The model assumes that both the aerodynamics and the structural dynamics of the assembly are linear, and retains the first-order terms of a fully consistent asymptotic expansion of the tuned system where the small parameter is the blade mistuning. The simplicity of the model allows the optimization of the blade mistuning pattern to achieve maximum rotor stability. The results of the application of this technique to realistic welded-in-pair and interlock low-pressure-turbine rotors are also presented.