Parametric Investigation of Pelton Turbine Injector under Hydro-abrasive Erosion Conditions

Abstract

In high-head Pelton turbines, the injector faces severe erosion due to suspended sediment leading to a reduction in turbine efficiency and higher maintenance costs. Here, the effects of design parameters such as the bend angle of the nozzle pipe, nozzle angle, and needle angle along with an operating parameter stroke ratio on hydro-abrasive erosion of Pelton turbine injector are numerically investigated. The Volume of Fluid (VOF) model was implemented for capturing the interphase between air and water; whereas, the SST k-ω model is used for modelling the turbulence effect. For tracking the discrete phase, a Eulerian-Lagrangian based Discrete Phase Model (DPM) is considered. The bend angles led to flow circulations in the nozzle pipe causing the non-uniform distribution of sediment concentration and uneven erosion patterns. Irrespective of the bend angle, the erosion hotspot in the needle is observed toward the bend side. Further, for larger sediment particles, higher bend angles lead to more erosion rate in both the nozzle and needle and must be avoided to prevent excessive damage. As the needle angle increases from 40° to 60° for a constant nozzle angle, the nozzle erosion rate increases by 70% and the needle erosion rate decreases by 99%. Hence, an injector design can be optimized in hydro-abrasive erosion conditions by selecting a needle angle between 40° and 60°. Further, the operation of the injector at too high and low a stroke ratio results in excessive erosion of the nozzle and needle, respectively. In this study, a stroke ratio of 0.45 is found to be the most suitable for hydro-abrasive erosion conditions. Moreover, the asymmetricity in the erosion pattern of the needle increases with needle angle and stroke ratio resulting in jet quality degradation, one major reason for efficiency reduction in Pelton turbines.