Numerical analysis of flow-induced noise in a waterjet propulsion pump at low speeds

Abstract Marine propulsion is a significant source of noise. In this study, a hybrid method coupling computational fluid dynamics and the acoustic-analogy theory is adopted to calculate the unsteady flow field and sound field of a waterjet propulsion pump. The sound pressure level of the pump exhibits an approximately circular distribution in the radial plane and distinct dipole characteristics in the axial plane, with amplitude decreasing with increasing frequency and vessel speed. The dominant sound pressure level frequency is the blade-passing frequency, with contributions from both the rotational and guide vane passing frequencies. Among all components, the inlet channel generates the highest sound pressure level. Considering pressure pulsations, the inlet channel is dominated by the blade-passing frequency, while the frequency in the internal regions of the pump evolve from the rotational to guide-vane-passing frequency, and finally to the blade-passing frequency, with notable amplitude variations between the wall-adjacent regions and the hub. Within the impeller, zones of high enstrophy align with abrupt changes in relative velocity. The vortex evolution in blade passages is mainly driven by the relative vorticity generation and Coriolis force terms. Particularly, near the suction side of the blade leading edge, strong enstrophy fluctuations significantly intensify the flow-induced noise in the pump.