Sediment-laden flow and erosion mechanisms in the Francis turbine upper crown cavity

Francis turbines often experience forced shutdowns due to functional failure in the upper crown cavity. However, the flow characteristics of sediment-laden flow and the mechanisms of sediment erosion within this cavity have not been fully elucidated. This study investigates sealing water leakage and sediment erosion in the upper crown cavity of Francis turbines, employing computational fluid dynamics based on the Hongshanzui Hydropower Station in Xinjiang. Numerical simulations using an Eulerian–Eulerian particle model were conducted across 432 operational cases, covering three flow rates, eight particle sizes, and nine sediment concentrations for two structural configurations of the upper crown cavity. This study established five key research metrics—namely, the flow characteristics of sediment-laden flow, the sealing performance of labyrinth seals, the discharge capacity of runner drain holes, the drainage efficiency of the head cover drain holes, and the sediment distribution—to evaluate the sealing, pressure reduction, and abrasion resistance performance of the upper crown cavity. Results show that the structure configuration significantly affects liquid-phase leakage flow patterns and sediment distribution. Moreover, sediment abrasion morphologies result from combined centrifugal and leakage-driven effects. The integrated runner pump enhances seal performance through pressure boosting and sediment collection, improving labyrinth seal effectiveness by 35.67%, reducing runner drain hole load by 62.85%, and increasing head cover drainage by 97.90%. This study systematically investigates sediment-laden leakage flow under multi-parameter conditions, revealing the flow characteristics of leakage water and clarifying the mechanisms of sediment erosion, thereby providing critical references for wear-resistant and energy-efficient design of the Francis turbine upper crown cavity.