Multi-scale sediment erosion mechanisms in the water distribution systems of Pelton turbines

As ideal hydraulic machines for high-head, low-flow hydraulic energy conversion, Pelton turbines are widely deployed in high-altitude mountainous regions. They play a crucial role in hydropower generation and water resource utilization. However, long-term operation with high-velocity sediment-laden water leads to severe erosion of key components such as the water distribution ring, injectors, and runner buckets. This erosion reduces turbine efficiency, shortens service life, increases maintenance costs, and poses safety risks. Thus, systematically investigating how sediment particle size affects the erosion characteristics of these components is theoretically and practically crucial, thereby providing technical support for optimal design, anti-erosion modification, and safe operation of the Pelton turbine. This study aims to examine the influence of sediment particle size on the erosion characteristics of the water distribution system.

This study employs the SST k–ω turbulence model, coupled with the discrete phase model, to perform unsteady three-phase (water–air–sand) numerical simulations of a six-nozzle distribution system.

The results show the following: 1) The multi-nozzle distribution system exhibits a notable flow-diversion effect. Particle trajectories show that the downstream channel receives a substantially reduced number of particles; consequently, erosion damage is primarily concentrated in the upstream channel and the first three injectors. 2) Secondary flow phenomena, particularly Dean vortices, arise from the combined effects of inertia and curvature within the water distribution ring. Erosion distribution correlates strongly with these flow structures, with damage concentrated near elbow sections, bifurcated pipe junctions, and internal vortex regions within the injectors. This indicates that erosion in the water distribution system is predominantly governed by secondary flow dynamics. 3) Particle properties have a remarkable impact on injector erosion. Fine sediment particles, due to their strong flow-following characteristics, mainly erode the needle surface. Moreover, residual Dean vortices are reactivated in the contraction section of the injector, intensifying particle accumulation in the vortex region and increasing the collision rate with the needle surface, thereby exacerbating needle erosion. 4) Large sediment particles exhibit strong inertial effects and poor flow-following characteristics, causing their trajectories to deviate considerably from streamlines and mainly erode the nozzle shell. 5) In a mixed particle-size group, a notable synergistic erosion effect is observed: fine particles primarily damage the needle surface, whereas large particles are more likely to impact the nozzle shell, further intensifying erosion in that area.

The multi-nozzle water distribution system demonstrates a pronounced flow diversion effect, substantially reducing the number of particles in the downstream channel. Consequently, erosion is primarily concentrated in the upstream channel and the first three injectors. Secondary flow and Dean vortices are prominent in the water distribution ring, with erosion predominantly occurring near elbows, bifurcated pipes, and internal vortex regions of the injectors, driven by secondary flow dynamics. Sediment particle size considerably affects the distribution and intensity of injector erosion. Fine particles, with strong flow-following abilities, erode the needle surface, whereas residual Dean vortices in the contraction section exacerbate this erosion. By contrast, large particles, with strong inertia and poor flow following abilities, deviate from streamlines and erode the nozzle shell. Mixed particle sizes exhibit a synergistic erosion effect, intensifying overall injector damage.