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

Objectives The vortex formed by the rotation of the toroidal propeller will be distributed to the entire blade, effectively preventing the tip vortex leakage, so that the vortex can be quickly dissipated in the water, reducing the propagation of hydrodynamic noise. However, due to its complex structure, it is difficult to model the toroidal propeller using conventional propeller modelling methods, so the parametric modelling equations of the annular propeller need to be studied. Methods The concept of propeller wheelbase is introduced to express the mathematical modelling equations of a toroidal propeller as a functional relationship that varies with wheelbase. A reference plane with the degree of angle α to the xy-plane of the toroidal propeller coordinate system is defined to ensure that the reference line of the toroidal propeller is on the reference plane that is α to the axis of rotation, and 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. Further, 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. Results It is found from the experimental results that under the same thrust condition, the toroidal propeller shows a great advantage in noise reduction, with the total noise sound pressure level at each measurement point on the circumference of a certain radius of the radial plane reduced by about 4 dB compared with that of the DTMB P4119 propeller, and that 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 4~6 dB compared with that of the DTMB P4119 propeller. Conclusions The proposed method can provide reference for the design of toroidal propellers, and the comprehensive analysis and evaluation of the noise level can provide a theoretical reference basis for the suppression of hydrodynamic noise of ships, underwater vehicles and other equipment, and at the same time provide technical support for the reduction of hydrodynamic noise of propellers of underwater vehicles and ships.