Numerical Study of Flutter Stabilization in Low Pressure Turbine Rotor with Intentional Mistuning

Abstract

Intentional mistuning concepts are used to mitigate the risk of flutter occurrence for compressor and turbine blades, as this design strategy represents one of the key aspects in nowadays turbomachinery aeroelastic design. In this paper, the effects of a mistuning pattern on LPT flutter stability are numerically investigated in order to highlight the differences with the classic tuned configuration. A LPT rotor is analysed with an intentional mistuning pattern composed by alternate blades with different additional masses at the blade tip, and the corresponding tuned configuration, consisting of the blisk (blade+disk) with identical blades. The first part of this work is devoted to the modal analysis for tuned and mistuned cases. Frequencies and mode shapes of the first bending mode family, obtained by FEM modal analysis in cyclic symmetry, are then used to perform CFD flutter analysis with moving blades. The results confirm the stabilizing effect of alternate mistuning pattern in contrast with the tuned system which denotes a strong flutter instability for a large range of negative nodal diameters. The numerically predicted flutter stabilization effect has been confirmed by measurements carried out during a tip timing experimental campaign performed within the Future EU project.