Unsteady Vibration Due to Cavitation in Mixed Flow Pumps

Abstract

In regarding to the large vertical mixed flow pump for seawater supply pump, the authors experienced the strange excessive vibration: the vibration level intermittently changed and the peak frequency was the blade passing frequency as like the vibration due to the submerged vortex in sump. In order to investigate the real cause, the model test was performed and it was found that the cause was due to the strong tip vortex cavitation on the blade surface of the impeller. As the countermeasure, the forward swept impeller was designed to suppress the strong tip vortex cavitation. After that, the model test had been performed to estimate the effect of the forward swept impeller on the cavitation condition. As the result, it was confirmed that the cavitation condition was drastically improved. Finally, the strange excessive vibration was disappeared in the actual pump by applying the improved impeller.