Tip-clearance pressure fluctuations between conventional pump-jet propulsor and pump-jet propulsor with rotor blade crown in non-uniform inflow

The suppression of the pressure fluctuations in the tip clearance of the pump-jet propulsor is of great significance in improving its noise radiation level. This study considers adding rotor blade crown structure to propose a new type of pump-jet propulsor. The hydrodynamic performance of conventional pump-jet propulsor and pump-jet propulsor with rotor blade crown was analyzed in non-uniform inflow conditions by conducting experimental tests and numerical simulation. The results show that after the introduction of the rotor blade crown, the open water coefficients of the two types of pump-jet propulsors show similar trends. However, the thrust and torque coefficients and the rotor blade propulsion efficiency of pump-jet propulsor with rotor blade crown are slightly smaller than those of the conventional pump-jet propulsor. Furthermore, the temporal and spatial distribution of the pulsating fluctuations of the blade tip clearance in the flow direction is changed, and the pressure fluctuations inside and near the clearance are suppressed. The line spectra characteristic of the pressure fluctuations of the blade tip clearance is all at the rotor blade passing frequency and its harmonics, and line spectra are all reduced to varying degrees. Theoretically, the range of rotor blade passing frequency line spectrum magnitude reduction is 2.78–24.07 dB, while the range of magnitude reduction obtained in the experimental test is 0.66–19.42 dB. This study provides an important theoretical basis and engineering reference for improving the noise radiation level of the pump-jet propulsors.