Types of aeroelastic vibrations of turbomachinery bladed discs

Abstract

A real process was analyzed for presence of self-oscillations. Absence of self-oscillations was revealed as its attributes such as progressive wave and beating were not discovered. A model of oscillatory process was proposed on the basis of the kind of oscillograms and the linear superposition theory for several simultaneously excited oscillation modes. In accordance with the theory two vibrations with frequencies equal to 919 and 469Hz were summed up. As a result of addition of these frequencies and comparison of the derived oscillograms with the real process it was found that the proposed model agrees with the original well enough. Moving further into the process, a third frequency component equal to 1002Hz originates in addition to those of 465 and 918 Hz. Addition of three frequencies carried out similarly to the first example also yields a satisfactory result. Oscillograms of real and model processes have a similar appearance. The frequency components calculated on the basis of the oscillogram of the model process practically coincided with the real process frequencies. Classification of aeroelastic oscillations was analyzed in order to determine the oscillatory type of the process under investigation. Three main phenomena were distinguished: forced oscillations, flutter and non-synchronous oscillations. Almost all foreign engine companies faced the latter phenomenon, sometimes mistaken for flutter. The analyzed example was labeled as non-synchronous oscillations according to features of non-synchronous oscillations, namely, aliquant rotation frequency and resonant behavior of oscillations.

Keywords

• oscillations of turbomachinery bladed discs
• self-oscillation
• linear superposition theory
• modeling
• non-synchronous oscillations