Aeroelastic Stability of Combined Plunge-Pitch Mode Shapes in a Linear Compressor Cascade

Authors

George Hill - Imperial College
Julian Gambel - Technische Universität Berlin
Sabine Schneider - Rolls Royce Deutschland
Sina Stapelfeldt - Imperial College London

Abstract

Modern aeroengines designs strive for peak specific fuel and thermal efficiency. To achieve these goals, engines have fewer and more highly loaded compressor stages, thinner aerofoils and blended titanium integrated disks (blisks) to reduce weight. Such configurations promote the occurrence of aeroelastic phenomena such as flutter. Two important parameters known to influence flutter stability are the reduced frequency and ratio of plunge and twist components in a combined flap mode shape. These are used as design criteria in the engine development process. However, the limit of these design methods is not fully understood and no systematic research studies exist which bridge the gap between simplified semi-analytical models and modern compressors.This research aims to close this gap by systematically investigating the stability of a linear compressor cascade using experimental and numerical methods. This paper focuses on the effect of reduced frequency and plunge-to-twist ratio. Using numerical simulations, which are compared against the experimental results for selected conditions, aerodynamic damping is computed for a range of frequencies and torsion axis locations. The results confirm the importance of these two parameters on compressor aeroelastic stability and prove that the critical parameter determining stability is the ratio of incidences induced by the plunge and twist motions.