Study on the transient cavitation characteristics in an axial flow tandem pump during the rapid starting period

In axial flow pump systems constrained by limited internal space, the advantages of axial flow tandem pumps are high space utilization, strong power capacity, and great thrust. The onset of cavitation during the rapid starting period poses a classic issue for tandem axial flow pumps, resulting in issues like noise, vibration, cavitation breakdown, and material damage. This article aims to investigate the transient cavitation characteristics of each flow passage component of an axial flow tandem pump during the rapid starting period by numerical simulation method. It is compared that the evolution laws of the cavity of each flow passage component. The evolution of the cavity in all flow passage components is strongly correlated with the flow rate change rate in each stage of the rapid starting period. Among all flow passage components, the first impeller firstly experiences cavitation, and its cavitation severity is also the most severe. The Effective Net Positive Suction Head (NPSH_a) can reduce the influence of transient effects on cavity prediction and better characterize the details of the cavity evolution in different impellers than the cavitation number σ during the rapid starting period. Meanwhile, The NPSH_a of the second impeller inlet is always higher than that of the first impeller inlet, indicating superior cavitation performance for the second impeller.