Influence of water quality on noise characteristics of sheet and tip-leakage vortex cavitating flow

Freestream nuclei, also referred to as water quality, are known to significantly affect cavitation inception. However, their effects on fully developed cavitation and the corresponding noise characteristics remain inadequately understood. In this study, a multiscale hydroacoustic model based on the Euler–Lagrangian framework is used to investigate the impact of water quality on monopole noise characteristics of sheet and tip-leakage vortex (TLV) cavitating flow. Cavitating flows over the National Advisory Committee for Aeronautics 0009 hydrofoil under varying water qualities are simulated, and the results are compared with those from the conventional Eulerian cavitation model and experimental observations. The findings indicate that the sound pressure radiated by sheet cavitation exhibits the same baseline signature across different water qualities, but more intense peaks are observed in nuclei-depleted flow. For TLV cavitation, a higher baseline acoustic signature is predicted in “weak” water, while a lower baseline signature with more extreme loud events is predicted in “strong” water, consistent with experimental observations. The corresponding cavity evolution shows that strong acoustic pressure pulses generated by sheet cavitation in strong water result from the more intense collapse and rebound of the sheet cavity. Additionally, the smaller baseline acoustic signature of TLV cavitation in strong water arises from the absence of tip-separation cavitation and the intermittency of TLV cavitation, while the stronger acoustic pressure pulse originates from the complete collapse of the TLV cavity, a phenomenon not observed in weak water. For both cavitation types, frequency-domain analysis reveals that monopole noise is amplified in the high-frequency range as water is degassed, likely linked to the dynamic behavior of the local cavities.