Suppression method for exciting force of pump jet propellers based on sinusoidal unevenly spaced rotor blades

A theoretical and numerical investigation has been carried out to understand the exciting force generation mechanism of the pump jet propeller (PJP) with evenly spaced and unevenly spaced rotor blades (ESB and UESB), which operates behind a standard submarine model. Firstly, the exciting force of ESB was studied by the Reynolds-averaged Navier–Stokes (RANS) method. Numerical methods were validated by calibration model tests and independent studies. The results show that the two main components exist in exciting force of the rotor: symmetric (f=aBPF, a is a natural number) and asymmetric (f≠aBPF) exciting forces, and the formation mechanisms of these exciting forces are explained by the interference theory. Then, the exciting force equations of UESB were derived, and the optimal modulation amplitude (S) of UESB was obtained as 4.6°. The numerical results have validated the theoretical prediction that the exciting force of the UESB is reduced by 12.6% at blade passing frequency (BPF). Finally, an optimization process for UESB based on theoretical prediction and numerical simulation was proposed, in which the efficiency of optimization was improved when the theoretical method was introduced. The research is beneficial for comprehensive understanding of the exciting force of PJP and practical engineering design of noise-reduced PJPs.