Noise reduction measurement and biomimetic propeller optimization designs for unmanned underwater vehicles

Biomimetic microstructured surfaces hold significant potential to alter the characteristics of flow fields and are actively being investigated for their role in noise reduction in the propellers of unmanned underwater vehicles (UUVs). However, accurately measuring the noise generated by UUVs remains a challenge, which complicates the validation of noise reduction strategies and leaves the underlying mechanisms insufficiently understood. In this study, we propose a general noise measurement method for UUVs that involves identifying the main noise sources, designing noise reduction strategies, and validating their effectiveness. Experimental results indicate that the propeller is the main noise source, prompting the design of biomimetic propellers incorporating serrated edges and surface microstructures inspired by humpback whales. These biomimetic propellers are subsequently installed on a UUV for testing, and the results demonstrate a significant noise reduction of up to 6.67 dB. To further validate the noise reduction effects, additional experiments are conducted to measure the motor power consumption and assess the hydrodynamic performance of the different propellers. The motor power consumption is slightly higher for the optimized propellers compared to the original design, indicating that the noise reduction effect can indeed be attributed to the changes in the propeller design, rather than fluctuations in motor performance. Additionally, the characteristic curves of the propellers revealed that while the biomimetic propellers produce lower thrust compared to the original propeller, they maintain stable performance across varying operating conditions. By combining experimental measurements with numerical simulations, we elucidate the underlying noise reduction mechanisms of biomimetic propellers, specifically the breakup of large-scale vortices into smaller, lower-energy vortices. This process reduces the energy of the large-scale vortices and redistributes it over a broader frequency spectrum. These findings provide a robust theoretical and experimental foundation for developing efficient, low-noise underwater propulsion systems, demonstrating profound academic and practical implications.