Experimental Flutter Investigations of an Annular Compressor Cascade: Influence of Reduced Frequency on Stability

Due to the trend of increasing power and reducing weight, the fan and compressor bladings of turbomachinery might be more sensitive to flutter, which must strictly be avoided already in the design process. In order to increase our understanding of the flutter phenomena for fan and compressor cascades, aeroelastic investigations are essential. This paper presents the achievements and results of experimental flutter investigations with a compressor cascade in the test facility of non-rotating annular cascades at EPFL. Flow conditions such as those that occur in rotating cascades are simulated by generating a spiral flow in the upstream. The construction of the cascade which takes into account the structural properties necessary to perform flutter experiments is described. For the simulation of elastic torsional vibrations of a two-dimensional blade section, the cascade consists of 20 blades (NACA3506 profile) mounted on elastic spring suspensions which allows for torsional motion about the midchord. In order to investigate the influence of the reduced frequency on the global stability of the cascade and its local contributions, experiments were performed for two different reduced frequencies. At the higher reduced frequency the cascade remains aerodynamically stable, however, at the lower reduced frequency and transonic flow conditions, some of the interblade phase angles appear to be aerodynamically unstable