Numerical investigation of flow around the injector of a Pelton turbine due to eroded needle

Abstract

Abstract Injectors of Pelton turbines are prone to both sediment erosion and cavitation. This causes degradation of the surface morphology, which aggravates the quality of the jet, lowering the turbine’s performance. The study focuses on CFD analysis of a groove-shaped erosion pattern on the needle and analyses its influence on the quality of the jet at the three stages of erosion. The numerical model comprises of a nozzle with a cylindrical passage for modelling the jet. The research used the SST turbulence model and boundary conditions defined according to the turbine’s data, from which the model was obtained. This study explores the impact of silt erosion on pressure signals around the injector of a Pelton turbine. Needle pressure distribution curves were plotted at various erosion levels and openings, revealing that pressure deviation increases with increase in erosion. The effect turns out to be minimal during high opening levels but becomes substantial as opening levels decrease. Operating in part load conditions leads to a significant pressure drop due to the reduction in flow rate. The pressure distribution tends to become more uniform at full load, achieving optimal flow rates. However, a noticeable pressure drop is observed in the eroded region, reaching a minimum at the deepest eroded area. The pressure drop is further amplified with an increase in the level of erosion, indicating erosion’s disruptive impact on fluid flow. The findings highlight the complex interplay between erosion, needle pressure distribution, and jet diffusion.