Investigation of Structurally and Aerodynamically Mistuned Oscillating Cascade Using Fully Coupled Method

Abstract

There seems to be a lack of clear and systematic understanding of physical behavior and mechanisms of mistuned blade rows, particularly in the context of the aerodynamic mistuning versus the structural (frequency) mistuning. A high-fidelity fully coupled method is desirable to investigate the vibration characteristics of aeroelasticity problems with strong fluid–structure interaction effects, as well as blade mistuning effects. In this work, the direct nonlinear time-domain fully coupled method is adopted to investigate the dynamics mechanism of a mistuned oscillating cascade. The main objectives are two-folds, first to elucidate the basic vibration characteristics of a mistuned blade row, and second to examine the aeroelastic effects of mistuning. Three conditions of interest are considered: (a) the structural mistuning only, (b) the aerodynamic mistuning only, and (c) a combination of the two. The present results show that first a mistuned configuration tends to vibrate with the same frequency and a predominantly constant interblade phase angle. Vibration amplitudes of the blades vary significantly with a strong mode localization effect for the structural mistuning. For the concurrent structural-aerodynamic mistuning, the localization is stronger than in the standalone structural mistuning case. Second, a monotonic increase of the aeroelastic stability with the structural mistuning magnitude is observed. On the other hand, the aerodynamically mistuned cascade shows a stabilizing effect with a small amount of mistuning but exhibits a destabilizing effect with a large mistuning. Furthermore, these results indicate a quite remarkable interplay between the structural and the aerodynamic mistuning. At a condition where the tuned cascade is still stable, an aero-mistuning induced unstable behavior is observed. An introduction of a large magnitude of frequency mistuning which would be stabilizing for a tuned cascade, is instead shown to have a destabilizing effect for the present combined aero-structural mistuning case.