The characteristic of pumps is required to sustain stable operation behaviour under all condi-tions. However, a pump’s operating range is often limited physically with the occurrence of the head curve instability in part load. This effect occurs when the head is increased continuously up to the maximum design head. This point is the physical limitation of the pump operation and is very difficult to predict properly by numerical design without a model test. The present study was realised within the scope of a joint research project with Andritz Hydro and the Institute for Hydraulic Fluidmachinery at Graz University of Technology. Its purpose is to identify the fluid mechanical phenomena leading to the occurrence of instabilities by combining numerical and experimental results. A reduced scale model of a radial ANDRITZ pump turbine with an nq of 45 was installed at a 4-quadrant test rig for the experimental investigation at unstable conditions in pump mode. The performed measurements were based on the IEC60193-standard. Character-istic measurements were carried out to get a thorough insight of the instabilities in pump mode. Particle Image Velocimetry (PIV) allowed the measurement of the velocity field in the vane less space between impeller and guide vanes and an additional optical access to the suction side of the model allowed visualizations of suction side part load flow and prerotation. Like never before the flow pattern in the draft tube cone became visible with the help of a High-Speed camera. Rotating vortices causing cavitation zones separated from the runner blade and extended into the draft tube cone against the main flow direction. These adverse pressure gradients in the diffuser cause flow separation and prerotation in part load. The interaction between the rotating impeller with the stationary diffuser (Rotor-Stator Interaction) as well as the dynamic pressure behaviour in the draft tube were analysed by dynamic pressure sensors. Significant velocity distributions detected by flow visualizations, a global overview of the dynamic pressure behav-iour and the measured head loss are the experimental outcome of the part load instability. In order to predict the point where the flow in a pump or a pump turbine is getting unstable a modi-fied setup for CFD-simulation was applied. Based on the results enhanced numerical simula-tions were carried out improving the numerical predictability of the instability in pump mode.
|Published - 13 Sept 2016
|3rd International Rotating Equipment Conference: IREC - Congress Center, Düsseldorf, Germany
Duration: 14 Sept 2016 → 15 Sept 2016
|3rd International Rotating Equipment Conference
|14/09/16 → 15/09/16
Fields of Expertise
- Sustainable Systems