Experimental Aeroelastic Investigation of Vibrating Turbine Blade Clusters

This paper presents and discusses unsteady experimental results of controlled vibration measurements of blade-cluster and single-blade test cases, all subjected to the same subsonic ow conditions. The experiments were performed in a non-rotating annular test facility with the aim to investigate the influence of cluster vibrations on the aerodynamic damping of turbine rotor blades. A frequently-used blade package type was selected: a two-blade-cluster in mixed mode, combing in a alternating manner a bending and a torsion vibration mode. In addition, single-blade test cases were investigated serving as reference for the cluster case. The actuation of the 20 turbine blades was obtained by an electro-magnetic excitation system, enabling individually 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. A comparison of the cluster- and the single-blade-test cases was performed and differences were identified and analyzed.