Radial pumps are used in a variety of applications. In many cases the pump operates under part-load flow conditions and the inflow condition differs from the dimensioning, optimal point, ultimately leading to flow instabilities. In this paper the influence of three different impeller blade designs are presented under stall conditions. All the impeller blades are designed for the same pressure rise over the impeller but using different concepts. The pump characteristic curves clearly show the changes concerning energy transmission and losses. Time-Resolved Particle-Image Velocimetry (TR-PIV) is used to investigate the onset and development of rotating stall within the centrifugal pump under part-load conditions. These measurements lead to detailed instantaneous velocity distributions during rotating stall. Fast-Fourier-Transformation (FFT) is finally carried out on the series of instantaneous measured flow fields to identify characteristic flow frequencies. The onset of rotating stall is observed for different part-load flow-rates for the three impellers under investigation.

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