Erosion in hydraulic power plants is caused by sand particles in the flow. This is one of the major problems that restricts the lifetime between overhauls of water turbines. Especially those parts of the hydraulic turbine which are exposed to high flow velocities bear a considerable risk of being damaged by erosion processes. Therefore, suitable methods for the prediction of erosion are necessary already in the design phase. The prediction of erosion, based on the Lagrangian calculation of particle paths in a viscous flow, will be described for two components of a Francis turbine, for which results of field tests have been available. As a first example, the flow field calculation and the mechanisms of erosion in a labyrinth seal will be described. It will be shown, that the erosion level is strongly dependent on the particle size. The comparison between the numerically obtained erosion pattern and the observations in the field tests shows good agreement for the labyrinth chamber walls. Unphysically high values are predicted for the entrance region into the second seal gap. A fully 3D flow and erosion calculation around the guide vanes of the same Francis turbine will be presented as the second example. It will be shown, that the geometry of the guide vane including tip clearance, support and fillets leads to a complex flow field (clearance flow, corner vortex) which, as a consequence, results in a complicated fluid-particle interaction strongly affecting the erosion pattern. The agreement between the numerically obtained erosion pattern and the field test measurements is very good even for local effects, i.e., on the gap surfaces and the support.
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