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

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 mistiming 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 mistiming, 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 hut 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.