Influence of twisted rudder on propeller line spectrum noise and rudder control force in submarines

As a new vibration and noise reduction measure, the twisted rudder in submarines improves propeller propulsion efficiency and reduces propeller excitation force. To fully understand the performance of the twisted rudder, the control force and propeller cavitation performance under small rudder angles were investigated. The propeller surface pressure pulsation was taken as a dipole sound source, and the low-frequency linear spectrum sound of the submarine propellers with conventional and twisted rudders under small rudder angles was numerically predicted employing an acoustic analogy method. The results showed that the twisted rudder improved the steering maneuverability and was beneficial for improving the cavitation performance of the propeller. The twisted rudder significantly reduced the main blade-passing frequency sound pressure level (1BPF SPL) of the propeller noise, which can reduce the average value of the 1BPF SPL of all monitoring points in the XY and XZ plane by more than 3.963 and 11.872 dB under different rudder angles, respectively. The results also exhibited a correlation between the reduction effect of the 1BPF SPL of the propeller and the reduction effect of the 1BPF amplitude of the unsteady force coefficient. The results have important military application value for submarine propeller noise reduction.