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

Aiming at ship propeller's cavitation low-frequency noise spectrum prediction,a hybrid method combining the cavitation viscous 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 was investigated.And the effects of thrust loads and cavity extension on the discrete line spectrum frequency and its spectrum source level were analyzed at last.The improved Sauer cavitation model and modified shear stress transport turbulence model 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 predict the cavitation low-frequency noise spectrum.Resultsshow that the 7-bladed propeller has the advantages of small loads,latter cavitation inception and low cavitating tonal noise indeed comparing to the 5 blades.Under the same cavitation index based on ship speed,the interaction of incoming inflow with blades will induce significantly low frequency line spectrum and strengthen its source level.Given the submarine wake,cavitation index and rotating speed,the thrust,torque and cavity area of blades will decrease with the load declining,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 spectrum will be depressed,and the spectrum level at 1 kHz reduces 2.54 dB also.The numerical method above constructs a numerical system to measure the cavitating hydrodynamics and noise performances of the ship propellers,and can be productive for the numerical design of wake adapted low noise submarine propeller.