Blade-vortex-interaction in an axial-flow pump sump: Impact on hydraulic performance and flow stability

Axial-flow pump is a key hydraulic equipment for low-head tidal pumping stations. However, the harmful vortices in the sump seriously damage the energy efficiency characteristics of the pump and restrict the development of hydropower and sustainable energy. This study examines an axial-flow pump with a closed sump, using hydraulic and pressure fluctuation tests, and high-speed visualization to understand the interaction between the suction vortices and blades, and their effects on energy efficiency and pressure fluctuations. The interaction between the roof-attached vortex (RAV) and the impeller blades, referred to as blade-vortex interaction (BVI), encompasses three stages: preparation, expansion, and erosion. During expansion and erosion, small vortices grow into larger vortex tubes and create dense vortices on the blade's suction surface. BVI-induced pressure fluctuations are highly unstable with increasing amplitude, and the FFT spectrum, ranging from 0 to fBPF, shows strong harmonic peaks. Additionally, the wavelet spectrum's energy shifts from low to high frequencies due to the dominant nonlinear broadband caused by vortices. Upon the integration of a novel joint anti-vortex device (JAVD), the energy profile of the pump apparatus was enhanced, resulting in a maximum reduction of hydraulic loss by 0.18 m. The efficiency apparatus has markedly increased, with a peak improvement of 2.2 %. Furthermore, the pronounced pressure fluctuation at the sump's roof has been substantially mitigated.