Impact of Runner Blade Trailing-Edge Material Loss on Flow Field and Pressure Pulsations in a Francis Turbine

Abstract This study investigates the effects of runner blade trailing-edge material loss on the internal flow characteristics and pressure pulsations of a Francis turbine. Transient full-flow numerical simulations based on the SST turbulence model were conducted under six operating load conditions (75%-100%) and four levels of blade material loss. Results indicate that under high-load conditions (90%-100%), increasing material loss enlarges the relative flow angle at the blade notch, reduces the absolute flow angle, and increases the circumferential velocity component. This increase expand the low-velocity region in the draft tube, strengthen vortex intensity, and aggravate flow instability. Pressure pulsation analysis shows that the low-frequency component at 0.3fn increases markedly throughout the flow domain with increasing material loss. At 100% and 95% load, the largest increase occurs in the spiral casing, where the pressure pulsation amplitude at SC01 increased by 361.6% and 490.6% for a 15 mm notch. Under 90% load, the maximum increase occurs in the vaneless region, where the mean pressure pulsation amplitude increased by 486.3% for a 15 mm notch. At lower loads (85%-75%), pressure pulsations become dominated by draft-tube vortex rope oscillations caused by loads reduction, resulting in irregular signal variations. Therefore, pressure pulsations under high-load conditions are recommended as reliable indicators for detecting runner blade trailing-edge material loss. This study provides a theoretical basis for pressure pulsation-based online diagnosis of blade material loss in Francis turbines.