An improved spectral method and experimental tests for the low-frequency broadband noise of marine propellers

Called by Green Ship of the Future to reduce the propeller noise pollution in the subsea environment and avoid the possibility of causing propeller-shaft-ship resonance, the low-frequency broadband noise (LFBN) of marine propellers was studied theoretically and experimentally. The spectral method is improved by considering the blade section thickness and anisotropy in the turbulence spectrum, both of which are found to be effective in improving the prediction accuracy when compared with the experimental results. A series of propellers with the same blade geometry but different blade number were tested in the large cavitation channel at the China Ship Scientific Research Centre. The peak values in all conditions were close to the first-order blade-passing frequency. The effects of blade number and the advance coefficient were investigated by testing the propellers operating under different conditions. The effects were also studied using both the spectral method and experiment, and the results were consistent. Furthermore, the quantitative dependence of the LFBN on the influencing parameters was investigated using the sensitivity analysis. The rotational speed and turbulence intensity were found to be the two main factors, with greater than 10% effects. In addition, the effects of thickness and anisotropy scaling factor were evaluated using the spectral method. The results of this study provide guidance for controlling the LFBN in propeller design and optimisation.