Parametric study of the aeroelastic response of mistuned bladed disks

Mistuning, imperfections in the cyclical symmetry of bladed disks, is unavoidable due to many factors, including manufacturing tolerances and in-service wear and tear. Even small mistuning levels can cause large changes in the dynamics of bladed disks because mistuning destroys cyclic symmetry. In particular, mistuning can cause mode localization and a drastic increase of the maximum forced response level. To study mistuning, classical finite element analyses (FEA) approaches become computationally expensive because mistuning requires the analysis of the full disk model. Recently, compact and accurate reduced order models (ROMs) of mistuned bladed disks considering only structural coupling between sectors have been developed. However, the incorporation of unsteady aerodynamic effects into these ROMs is limited despite the fact that accurately accounting for the aerodynamic blade-to-blade coupling is essential for predicting mistuning effects in turbomachinery. Previous studies by the authors have shown that aerodynamic coupling can have important effects on the dynamics of bladed disks for subsonic flows. In particular, differences in the aerodynamic damping affect significantly the forced response amplification factor, and aeroelastic mistuned mode shapes differ significantly from the structural ones. These phenomena are accentuated in the transonic regime, where the presence of the shock creates a stronger blade-to-blade coupling than in the subsonic regime, as demonstrated herein. Parametric studies are conducted for various inflow Mach numbers and incidence angles. It is shown that the effect of aerodynamic coupling diminishes when the inflow Mach number is smaller, while the differences in the aerodynamic damping values still affect significantly the dynamics of mistuned bladed disks. Also, severe mistuned mode localizations are observed for modes having separated frequencies due to frequency veering.