Experimental and Analytical Mistuning Analysis of a Blisk at Lab Conditions and Under Rig Conditions Using Tip Timing

Determination of the amplification factor due to mistuning is an important task for the safe design of turbomachinery, specially for blisk-design with low mechanical damping. The complexity of the environment effects increases from measurements in the laboratory to measurements in test rigs and engines. Also the uncertainties of the boundary conditions increase. In this paper measurements of the amplification factors due to mistuning at various conditions are presented, starting from simple lab measurements up to rig measurements. Calculations with a Reduced-Order Code based on measured frequency distributions and FEM are performed and compared with the measurements. For the determination of the amplification factor a mistuning rig with travelling wave excitation was built. For a small demo-blisk the amplification factor was determined. Then a real blisk was tested. Afterward, the same blisk was built into a two-stage axial compressor rig. Here, tip-timing measurements were performed under rig conditions (centrifugal force, flow conditions). As tip-timing measures the vibration amplitude of each single airfoil, an amplification factor can be determined for each resonance.