Abstract: Pelton turbines are suitable for converting the hydropower of medium, high and ultra-high heads, and has broad application prospect for harvesting high head hydropower in Southwest China. In this work, numerical simulations of the three-dimensional multi-phase flow were conducted in a model Pelton turbine designed for the Zixia hydropower plant in Tibet, focusing on its hydraulic performance and internal flow characteristics impacted by a single jet with five different openings. The predicted results show that under the design operating head, the hydraulic efficiency of the turbine reaches the highest under the optimal opening, and lowers as the opening deviates from its optimum. Hydraulic efficiency variation varies gently between the range of 0.75 to 1.60 times of the design discharge, with an efficiency drop less than 1% from the optimum. The comparative analysis of the unsteady flow behaviors in the runner bucket at three different opening conditions reveals the occurrence of leakage discharge at the bucket cutout, which aggravates significantly as the opening exceeds the optimum, accounting for the increase in hydraulic loss. This study provides reference for the design of the Zixia hydropower plant 230 MW large capacity Pelton turbine unit.

Key words: Pelton turbine runner, opening, hydraulic performance, unsteady water sheet flow, numerical simulation