Radiated noise from cavitation bubble volume pulsation in a shaftless pump-jet propulsor

The radiated noise resulting from cavitation bubble volume pulsations is a critical component of cavitation-induced noise during propulsor operation. This paper investigates the radiated noise generated by cavitation bubble volume pulsations in a shaftless pump-jet propulsor. Utilizing spherical bubble acoustic radiation theory, a numerical simulation method was developed to analyze this phenomenon. Additionally, the effects of distance, cavitation number, and flow rate on the radiated noise were examined. The research findings indicated that an increase in flow rate or cavitation intensity leads to a rise in the average cavitation bubble volume within the propulsor impeller. The sound pressure level spectrum of the radiated noise in the propulsor exhibits a continuous spectrum. The sound pressure level initially increases slightly and then continuously decreases with increasing frequency. At a constant flow rate and cavitation stage, the sound pressure level of pulsating radiation noise generated by cavitation bubble volume decreases as the distance between the measurement point and the noise source increases. with the gradient of this reduction progressively diminishing. Additionally, at the same flow rate, the sound pressure level of the radiated noise in the propulsor initially shows a slight increase, followed by a gradual decrease across different cavitation stages, with the characteristic frequency corresponding to the blade passing frequency. As cavitation intensifies, the overall radiated noise increases, while the prominence of the blade frequency diminishes. Furthermore, as the flow rate increases, the cavitation bubble volume pulsations intensify, leading to a corresponding rise in the overall sound pressure level of the radiated noise within the propulsor. This effect becomes more pronounced as the severity of cavitation increases. The findings of this study provide valuable insights into the noise control of shaftless pump-jet propulsors.