Session: 22-04 Turbine Aerodynamic Excitation and Damping

Paper Number: 127528

127528 - The Role of Operating Conditions on Flutter Instability of a Low-Pressure Turbine Rotor 

Modern trends in low pressure gas turbine design lead to lighter designs with fewer stages, thinner sections and highly loaded components. Blades are thus more prone to flutter induced vibrations that can compromise their structural integrity.

Accurate predictions of flutter inception and evolution remains a challenging task. Several numerical methods have been developed for a long time and dedicated experimental campaigns have been carried out to have a better insight of flutter problems. The ARIAS EU project provided the opportunity to investigate flutter occurrences of turbine and compressor rotors with unique test benches and to try state of the art numerical techniques.

In this context, the paper discusses the impact of the turbine operating conditions on flutter inception of an unstable low pressure turbine rotor, extensively tested during the ARIAS project. The operating conditions were changed by modifying the rotor rotational speed, and the first bending and torsion mode families of a cantilever configuration have been analyzed. Numerical results reveal that an increase of the rotational speed leads to more unstable configurations for the bending mode-shape, while the torsional mode-shape moves from stable to unstable condition when lowering the rotational speed. Such numerical evidence has been confirmed by the blade tip timing acquisition technique also in terms of most unstable nodal diameter.

Moreover, a numerical strategy to assess flutter oscillation amplitudes by using acoustic measurements has been developed and validated against tip timing acquisitions. This combination of numerical results and experimental data leads to a better understanding of the physical processes that cause such asynchronous vibrations.

Presenting Author: Lorenzo Pinelli University of Florence - Department of Industrial Engineering

Presenting Author Biography: Lorenzo is an assistant professor at the Department of Industrial Engineering of the University of Florence. Lorenzo’s research is largely concerned with computational aeroelasticity and aeroacoustics in turbomachines. His principal interests are in the development of numerical methods for flutter, forced response and noise analysis in multi-stage turbomachines.

Authors:

Lorenzo Pinelli University of Florence - Department of Industrial Engineering
Francesco Poli University of Florence
Andrea Arnone University of Florence
Antonio Giuseppe D' Ettole Avio Aero – GE Aviation Business
Emanuele Rosso Avio Aero – GE Aviation Busines
Gianmaria Sartor Avio Aero – GE Aviation Business
Vsevolod Kharyton Siemens Energy AB