Abstract
This study aims to demonstrate the merits of pressure-relieving holes at the tip region of propellers, which is introduced as “PressurePoresTM” technology as a retrofit on marine propellers to mitigate tip vortex cavitation noise for a quieter propeller. Shipping noise originates from various sources on board a vessel, amongst which the propeller cavitation is considered to dominate the overall radiated noise spectrum above the inception threshold. Thus, by strategically introducing pressure-relieving holes to modify the presence of cavitation, a reduction in the overall cavitation volume can be achieved. This mitigation technique could consequently result in a reduction of the radiated noise levels while maintaining the design efficiency as much as possible or with the least compromise. The strategic implementation of the holes was mainly aimed to reduce the tip vortex cavitation as this is one of the major contributors to the underwater noise emissions of a ship. In this paper, the details and results of a complementary numerical and experimental investigation is presented to further develop this mitigation concept for underwater radiated noise (URN) and to validate its effectiveness at model scale using a research vessel propeller. An overall finding from this study indicated that a significant reduction in cavitation noise could be achieved (up to 17 dB) at design speed with a favourable strategic arrangement of the pressure pores. Such a reduction was particularly evident in the frequency regions of utmost importance for marine fauna while the propeller lost only 2% of its efficiency.
Highlights
The technological developments over the last half-century have revolutionised the world that we live in
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Summary
The technological developments over the last half-century have revolutionised the world that we live in. With the ever-increasing world population, the volume of commercial shipping has been experiencing an increasing trend over the last five decades. This has resulted in the elevation of emissions produced by the maritime industry [1]. The extraordinary expansion of the world fleet has resulted in increased levels of ambient noise in the world’s seas, especially in the low-frequency domain [3]. This domain is utilised by marine mammals for their various fundamental living activities. Exposing them to such an abrupt change in ambient noise levels may disorient them or disrupt their communication signals, leading to behavioural changes of these mammals and local extinction [4,5]
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