Underwater radiated noise reduction technology using sawtooth duct for pumpjet propulsor

Marine Environmental Protection Committee (MEPC) and other organizations have made calls to develop regulations for limiting noise levels at sea. The propeller noise plays an important role in underwater radiated noise. Pumpjet propulsor (PJP), as a new type of propulsion system, is widely used in underwater vehicles. A propeller noise reduction technology using sawtooth duct is proposed and applied for the first time to PJP. In this paper, a normal PJP model and a PJP model with the sawtooth duct are presented to investigate effects of the sawtooth duct on hydrodynamic and noise performances. Flow of the models is simulated using a commercial CFD software, and noise is predicted based on DES simulation and FW-H equation. Results show that the sawtooth duct results in 2% of maximum water efficiency loss. The sawtooth duct directly changes the morphology of wake vortices, and reduce the TKE value at most of the wake region of PJP. Furthermore, the sawtooth duct can significantly reduce the noise generated by PJP from 10Hz to 5000Hz, especially in the low-frequency below 1000 Hz. The overall SPL of PJP is reduced about 2.5-5 dB by sawtooth duct with the maximum reduction 4.88 dB at the design point.