Numerical study of cavitation and noise characteristics of a five-bladed toroidal propeller

Objectives To clarify the changes in cavitation, hydrodynamic and acoustic characteristics when the blade number of a toroidal propeller increases from three to five, and to distinguish the effects of configuration and load level on acoustic radiation. Methods The David Taylor Model Basin (DTMB) P4119 propeller and three- and five-bladed toroidal propellers were investigated using a steady Reynolds-averaged Navier-Stokes (RANS) solution to initialize a transient large eddy simulation (LES), coupled with the Schnerr-Sauer cavitation model and the Ffowcs Williams-Hawkings acoustic analogy (FW-H). Equal-speed and equal-thrust conditions were compared. Results The cavitation inception speeds on the pressure and suction sides of the five-bladed propeller were 1,050 and 1,480 r/min, 75% and 34% higher than those of the three-bladed propeller. At 1,100 and 1,200 r/min, the vapor-volume coefficients decreased by 72.38% and 51.42%. At 600 r/min and J=0.833, thrust increased by 20.4%. At an equal thrust of 245 N, the five-bladed propeller speed decreased from 600 to 547 r/min and the propulsive efficiency decreased from 56.94% to 55.66%; the overall sound pressure levels decreased by 3.385 and 8.589 dB at P1 and P3, respectively, but increased at P2 and the axial points P4–P6. Conclusions The five-bladed configuration improves cavitation margin and thrust capability by increasing circumferential loading continuity, and reduces the required rotational speed under the same thrust demand, although with a slight decrease in propulsive efficiency. Its acoustic benefits exhibit pronounced directional dependence, and further optimization is required to reduce broadband noise in the vicinity of P2 and in the axial wake region.