The leakage flow induced by the end clearance of guide vanes in Francis turbines significantly impacts unit efficiency and sediment erosion characteristics. Existing numerical studies often neglect the influence of guide vane clearance, leaving the mechanistic role of clearance flow in sediment erosion characteristics poorly understood. This study systematically investigates the influence of four clearance schemes (ranging from 0 to 2.6 mm) on the flow dynamics and erosion patterns in a high-head turbine using a numerical simulation approach for solid–liquid two-phase flow. The results reveal that increasing the clearance not only markedly reduces hydraulic efficiency (with efficiency declines of 0.4%, 2.0%, and 4.0% for clearances of 0.52 , 1.82 , and 2.6 mm, respectively) but also transforms the leakage vortex structure in the guide vane domain from a single elliptical form into an intensified Y-shaped configuration. Sediment particles undergo two 90° deflections within the clearance, leading to pronounced erosion zones near the guide vane pivot, trailing edge, and upper/lower cover plates, with erosion severity escalating alongside clearance enlargement. The evolution of leakage vortices distinctly alters erosion distribution, causing the erosion regions on the cover plates to coincide with the vortex projection areas. Notably, the impact velocity and erosion rate at the lower ring side of the blade suction surface leading edge increase substantially with larger clearances, indicating that excessive clearance dimensions critically exacerbate erosion damage in this region. The study establishes quantitative relationships between guide vane clearance size, efficiency loss, vortex evolution, and erosion characteristics, offering valuable insights for elucidating sediment-induced erosion mechanisms and optimizing anti-erosion designs in Francis turbines.
Sun et al. (2025) studied this question.