Numerical Study of Erosion in Pelton Injector System Implementing the Effect of Gravity on Lagrangian Particles with Different Size

The spear valve is among the most vulnerable part of a Pelton turbine system operating in rivers with sediments. The spear valve regulates water flow into the Pelton buckets. The erosion is found to be severe while operating in low opening condition. The numerical study focuses on the erosion study for low opening of 25%. From the past literatures using Computational Fluid Dynamics (CFD) method, it was found that the implementation of gravity on the sediment particles was neglected to decrease the computational burden, especially for the simulation of turbines where the flow velocity was too high and the gravitational effect was considered negligible. This research employed a Lagrangian-Eulerian model to numerically investigate the erosion behaviour of the Pelton injector components using OpenFOAM. The sediment particle flow and characteristics were coupled with the fluid flow using the OpenFOAM Lagrangian library. A transient simulation was run with and without the inclusion of gravitational effects on Lagrangian particles to examine the real-time behaviour of sediment flow and erosion patterns in the spear valve. Using gravity on sediment particle provided over estimation of erosion in the direction of gravity comparing with the real case erosion. So, the erosion results were more realistic while not defining the extra gravity parameter for the particle. For, erosion simulation Finnie erosion model was used and no gravity effects were defined for the particle. Similarly, various sizes (50 μm, 100 μm and 200 μm) of sediment particles have also been applied to study the erosion rate and erosion patterns in the spear valve, seat ring and nozzle. Asymmetric erosion pattern was observed in the needle and erosion region increased with size. No erosion was observed near tip and tip region of spear valve. In nozzle the erosion was more concentrated in the nozzle outlet region for smaller sizes but the erosion region got extended to the nozzle tapering region with increase in size. For seat ring, simply the erosion increased with larger particle size.