PREDHYMA

Hydro-abrasive erosion

Thursday 19 March 2015

Turbines of hydropower plants suffer from a gradual damage caused by the impact of small sediments, which are contained in stream waters. This gradual damage leads to a change of shape of the turbine buckets so that the efficiency of the machine can be found to decrease rapidly. Costly maintenance or replacement of the turbine follows as consequence. Particularly Pelton turbines suffer from hydro-abrasive erosion due to the high kinetic energy of the abrasive particles. Determination of the material removal in function of time, sediment concentration and size is challenging manufacturers in order to predict reliably the decrease of efficiency in front of customers. Therefore it is essential to identify and characterise the damage mechanism of particles impacting the turbine, which is mainly dependant on the impact velocity and impact angle of the sediment in relation to the turbine’s bucket surface.

The work aims to numerically predict the damage caused by the small sediment particles on the turbine’s surface in time and space. In order to properly define a particle’s impact velocity and angle of impact, its behaviour in a jet stream impacting a Pelton turbine bucket has to be accurately defined. Therefore turbulence, the movement of dispersed particles in the fluid and under wall influence have to be implemented macroscopically into a code based on smoothed particle hydrodynamics (SPH) internally developed by Andritz Hydro AG. Two-way coupling of the continuous and dispersed phase have to be taken into account as well as a coupling of the SPH code for the fluid with a finite element formulation for the solid to investigate the particle impact in a microscopic scale.


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