Propeller cavitation viscous simulation and low-frequency noise prediction with non-uniform inflow

Aiming at predicting ship propeller’s cavitation low-frequency noise spectrum,a hybrid method combining the cavitation multi-phase flow unsteady simulation with the pulsating spherical bubble radiated noise theory was proposed.Then,both of the NSRDC4383 5-bladed propeller and a 7-bladed highly-skewed propeller’s cavitation low-frequency noise spectrum subjected to the full appended SUBOFF submarine’s nominal wake were investigated.The effects of thrust loading and cavity extension on the discrete line spectrum frequency and its spectrum source level were analyzed.The improved Sauer cavitation model and modified shear stress transport turbulence models were adopted to simulate the propeller sheet cavitation along with integrated verification.The cavity volume acceleration related to the characteristic length representing the unsteady sheet cavitation extension,which was more reasonable than the spherical cavity hypothesis,was used to the cavitation low-frequency noise spectrum prediction.Results show that the 7-bladed propeller truly appreciates the advantages of smaller loads,latter cavitation inception and lower cavitating tonal noise comparing to that of the 5 blades.Under the same cavitation index based on ship speed,the interaction of wake inflow and blades will induce significantly low frequency line spectrums and strengthen their source level.Given the submarine wake,cavitation index and rotating speed condition,the thrust,torque and cavity area of blades will decrease with the decreasing load,but the fluctuated acceleration amplitude of cavity volume and the tonal noise spectrum level increases,and the discrete line spectrum components shift mainly to the even times of the BPF harmonics from the odd.If the cavitation extension lightens,the BPF harmonics line spectrums will be depressed,and the spectrum level at 1 kHz reduces 2.54 dB.The numerical method above constructs a numerical system to measure the cavitating hydrodynamics and noise performances of ship propellers,which can be productive for the numerical design of wake adapted low noise submarine propeller.