Dynamic loads in turbomachines may lead to severe fluid induced vibrations, in particular, if resonance conditions are matched. The major sources of such unsteadiness are ro-tor/stator interaction, flow separation on the blade suction side at part-load and separation due to the curvature of the shroud. In the present work, some of these phenomena are investigated using computational techniques (Computational Fluid Dynamics - CFD) as well as novel measurement methods (High-Speed Particle Image velocimetry - PIV). The measurements provide a unique database of the velocity fields in an industrial impeller at various operation conditions. They are the base for validation of the computational methods. In view of the complexity of the separated, transient and turbulent flow field, this is still an open issue. Besides that, the analysis of the transient flow fields allows the determination of the "modes" of unsteady forces und thus, to shed some light on the sources of unsteadiness in the flow.
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