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Cavitation erosion in hydraulic turbines
Dr Magdalena Neuhauser (Andritz Hydro, CH)

Cavitation can cause damages in all types of hydraulic turbines from turbines with low head and large discharge to turbines with high head and small discharge. If possible turbines are designed in order to avoid cavitation in the whole operating range. CFD and reduced scale model tests allow to assess the risk of appearance of cavitation for a specific design.Since it is not always possible to avoid cavitation for all operating points, it is important to understand the mechanisms of cavitation erosion in order to evaluate the risk of damages in a turbine even if cavitation occurs. There are two main axes of research within ANDRITZ Hydro aiming at minimizing the occurrence of damages due to cavitation erosion. On the one hand coupled fluid structure simulations, like Smoothed Particle Hydrodynamics (SPH-ALE) for the fluid coupled to finite element analysis (FEM) for the structural part, are carried out to understand erosion at the microscopic scale of a bubble collapse. On the other hand different materials are tested for their resistance to cavitation erosion in dedicated cavitation erosion test rigs. These cavitation test rigs also allow to check the influence of several parameters and geometries, to visualize cavitation by high speed videos and to develop procedures that might help assessing cavitation erosion at reduced scale model tests like for example paint tests.