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

Abstract

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 numerical results demonstrate that material loss weakens the flow-guiding capability of the blades, inducing kinematic slip in the circumferentially averaged outlet velocity triangle. This leads to an increase in the relative flow angle (β), which significantly enhances the tangential velocity (Vu) and the swirl number (Sr). As the material loss b increases, the expansion of the low-velocity backflow zone exacerbates the blockage effect within the draft tube, resulting in a continuous decline in hydraulic efficiency. Frequency-domain analysis reveals that blade material loss significantly amplifies pressure pulsations at the 0.3fn characteristic frequency. Specifically, at monitoring point SC01, a notch width of 15 mm leads to increases in pressure pulsation amplitude of 361.6%, 490.6%, and 466.2% under 100%, 95%, and 90% load conditions, respectively. In contrast, medium-load conditions (75%–85%) exhibit a nonlinear response to the increase in Vu induced by material loss. Ultimately, these findings demonstrate that variations in 0.3fn serve as a robust indicator for monitoring runner blade material loss, with optimal diagnostic sensitivity achieved at Sr < 0.4 in the draft tube.