Numerical study of nozzle erosion and its cascading impact on jet quality

Abstract Sediment erosion is one of the major factors affecting the overall efficiency of hydro-turbines working under sediment laden conditions. The erosion not only decreases the efficiency but also changes the flow characteristics. However, the research regarding the changes in flow characteristics due to erosion is limited. The objective of this study is to identify the changes in flow characteristics of a Pelton nozzle due to erosion. Particularly, in a Pelton turbine system, the nozzle and the bucket are the components that are mostly affected by the erosion. The flow in the nozzle is unaffected by the erosion in the bucket. Nonetheless, the overall flow characteristics in the bucket can be affected by nozzle erosion. The erosion in the nozzle decreases the jet velocity and make it bit more dispersed which eventually decreases its impact force on the bucket and eventually leads to the decrement in overall efficiency of the turbine. A numerical study was conducted to compare the pressure loss, jet diameter, velocity, and dispersion angle between eroded and uneroded nozzle. Some wavy perturbations were induced on the needle and nozzle casing of the reference uneroded case to create the eroded nozzle case. The CFD simulation was then performed in OpenFOAM using its inbuilt multiphase solver, incompressibleVoF (interFoam). It was observed that, with erosion the total pressure loss, jet diameter, and dispersion angle increases but the velocity of the flow decreases. If these changes in flow get detected during operation, it can be used to develop real-time condition monitoring system.