Experimental Aeroelastic Investigation of Vibrating Turbine Blade Clusters

The presented work consists of the presentation and discussion of unsteady experimental results of controlled vibration measurements for two single-blade and two cluster test cases subjected to the same subsonic flow conditions. The experiments were performed in a non-rotating annular test facility with the aim of investigating the influence of cluster vibrations on the aerodynamic damping of turbine rotor blades. Two frequently-used blade package types were selected: a two-blade-cluster in bending mode and a four-blade-cluster in torsion mode. In addition, single-blade test cases were investigated serving as reference for the cluster cases. The actuation of the 20 blades was obtained by an electromagnetic excitation system, enabling the adjustment of vibration amplitude and phase for each blade at one vibration frequency. The unsteady measurements obtained include time-synchronous unsteady blade surface pressures and blade displacements resulting in local and global aerodynamic blade damping. The comparison between single-blade and cluster test cases identified similarities with the distribution of local aerodynamic damping on the outer cluster-blades.