Marine ducted thruster underwater radiated noise control through leading-edge tubercle blade modifications - a numerical hybrid approach

Anthropogenic-related underwater radiated noise (URN) has a detrimental impact on marine creatures who utilise the acoustic environment to perform basic living functions. Ambient ocean noise levels are increasing due to the growth of global shipping activity, where the propeller under cavitating conditions typically dominates the URN signature of marine vessels. Therefore, reducing cavitation severity and the subsequent URN is critical for future marine craft. This paper aims to assess the noise mitigation capability of LE tubercles on a benchmark Kaplan-type ducted propeller blade in cavitating conditions using computational fluid dynamics (CFD), detached eddy simulations (DES) are implemented to solve the hydrodynamic flow-field and the Schnerr-Sauer model is used to describe the cavitation behaviour. Both near and far-field noise is predicted within the hydroacoustic analysis. The Ffowcs-Williams Hawkings (FW-H) acoustic analogy was utilised to propagate the generated noise into the far-field. In summary, it was found that the LE tubercle modified ducted propeller blades could produce a noise reduction in the far-field at most test conditions considered to a maximum of 6dB overall average sound pressure level (OASPL). This is believed to be predominantly due to the introduction of the counter-rotating vortex pairs and subsequent alteration of the local pressure field over the blade suction side, which ultimately reduces the sheet cavitation severity over the blade surface by funnelling the cavitation behind the tubercle trough region.