Stability analysis of a low-head vertical box-culvert axial flow pump device under cavitation conditions based on model test

To investigate pressure fluctuation, vibration, and noise characteristics of a low-head vertical box-culvert axial flow pump device under both non-cavitating and cavitating conditions, a model test approach was employed. This study primarily examined the time-frequency characteristics of pressure fluctuation and the variations of vibration and noise with flow rate under these conditions. The results indicate that under non-cavitating conditions, the dominant pressure fluctuation frequency in the outlet passage is at rotational frequency, while at the impeller inlet, it occurs at four times rotational frequency (i.e., blade passing frequency, BPF). The dominant pressure fluctuation frequencies remain unchanged between cavitation and non-cavitation conditions. As the required net positive suction head (NPSHr) decreases, the pressure pulsation coefficient at the impeller inlet decreases from 14.73 kPa under non-cavitation conditions to 4.48 kPa under deep cavitation conditions. The developed cavitation results in a 41.0% reduction in radial vibration and a decrease in noise levels of 7.9% and 8.3% at the outlet and blind ends of the discharge passage, respectively, when compared to non-cavitation conditions. The intensification of cavitation suppresses the generation of pressure fluctuations and the development of internal flow-induced noise. This study provides valuable insights into the stable operation of low-head vertical box-culvert pump stations under cavitating conditions.