Design of a new parametric method for low-noise toroidal propeller and its hydrodynamic noise study

The vortex generated by the toroidal propeller's rotation is distributed across the entire blade, effectively preventing tip vortex leakage and allowing the vortex to dissipate rapidly in water, thereby reducing the propagation of hydrodynamic noise. However, its complex structure poses challenges for conventional propeller modelling methods, necessitating the study of parametric modelling equations for the toroidal propeller.

The concept of propeller shaft spacing is introduced to express the mathematical modelling equations of a toroidal propeller as a functional relationship dependent on the shaft spacing. A reference plane is defined at an angle α to the xy-plane of the toroidal propeller coordinate system, ensuring that the reference line of the toroidal propeller lies on the reference plane, which is inclined at an angle α to the axis of rotation. The parameters of the toroidal propeller are taken as the reference line, and the NACA airfoils distributed along the reference line are constructed based on the Class-Shape Function Transformation (CST) method to form a three-bladed toroidal propeller model. Furthermore, the FW−H acoustic analogue equation is introduced to compare the flow field and non-cavitation noise between the toroidal propeller and the DTMB P4119 propeller.

The experimental results show that, under the same thrust condition, the toroidal propeller shows a great advantage in noise reduction. The total noise sound pressure level at each measurement point on the circumference of a certain radius of the radial plane is reduced by about 4 dB compared with that of the DTMB P4119 propeller. Similarly, the total noise sound pressure level at each measurement point on the circumference of a certain radius of the axial plane is reduced by about 4 to 6 dB compared with that of the DTMB P4119 propeller.

The proposed method provides a useful reference for the design of toroidal propellers. The comprehensive analysis and evaluation of noise levels offer a theoretical reference basis for suppressing hydrodynamic noise in ships, underwater vehicles and other equipment, while also providing technical support for reducing hydrodynamic noise from propellers of underwater vehicles and ships.