Test Rig

A description of the test rig and the measurements are given in [5]. From the two measured operation points, the high-pressure ratio operation point is selected for the current study. The total pressure ratio of 2.72 causes a transonic flow through the turbine stage.

The unsteady flow measurements were performed on a rigid rotor at con­stant speed. The forced response experiments, on the other hand, were done on a rotor with flexible blades with resonant frequencies close to the vane passing frequency. This rotor was accelerated through the resonance of interest, and the blade vibration amplitudes were measured using strain gauges. The eigen – frequencies and the mode shapes were also determined in a clamped block. The measured torsional eigenfrequencies of the 64 blades for clamped condi­tions vary between -6.8% up to +1.8% with respect to the mean frequency indicating significant mistuning [5], [10].

The analysis of Seinturier [10] shows that the mean of the amplitudes of the mistuned system is only 89% of that of the equivalent tuned system.