Hydroacoustic and hydrodynamic investigation of bio-inspired leading-edge tubercles on marine-ducted thrusters

Abstract

Underwater radiated noise (URN) has a negative impact on the marine acoustic environment where it can disrupt marine creature's basic living functions such as navigation and communication. To control the ambient ocean noise levels due to human activities, international governing bodies such as the International Maritime Organization (IMO) have issued non-mandatory guidelines to address this issue. Under such framework, the hydroacoustic performance of marine vehicles has become a critical factor to be evaluated and controlled throughout the vehicles' service life in order to mitigate the URN level and the role humankind plays in the ocean. This study aims to apply leading-edge (LE) tubercles of the humpback whales’ pectoral fins to a benchmark ducted propeller to investigate its potential in noise mitigation. This was conducted using CFD, where the high-fidelity improved delayed detached eddy simulations (IDDES) in combination with the porous Ffowcs-Williams Hawkings (FW-H) acoustic analogy was used to solve the hydrodynamic flow field and propagate the generated noise to the far-field. It has been found that the LE tubercles have shown promising noise mitigation capabilities in the far-field, where the OASPL at J = 0.1 was reduced to a maximum of 3.4 dB with a maximum of 11 dB reduction in certain frequency ranges at other operating conditions. Based on detailed flow analysis researching the fundamental vortex dynamics, this noise reduction is shown to be due to the disruption of the coherent turbulent wake structure in the propeller slipstream causing the acceleration in the dissipation of turbulence and vorticity-induced noise.

Hydroacoustic analysis of a marine propeller using large-eddy simulation and acoustic analogy

“…(2021 b , 2022) proposed a fix to this problem. The porous approach was recently pursued by Stark & Shi (2021) and Kimmerl, Mertes & Abdel-Maksoud (2021). In particular, Stark & Shi (2021) analysed the acoustic signature of four-bladed ducted thrusters, using data from improved delayed detached-eddy simulation (IDDES), conducted on an unstructured hexahedral mesh consisting of about 13 million elements.…”

“…In addition, the porous formulation is typically affected by the issue of the spurious sound due to the eddies crossing the permeable surface of integration, although the recent works by Zhou, Wang & Wang (2021a) and Zhou et al (2021bZhou et al ( , 2022 proposed a fix to this problem. The porous approach was recently pursued by Stark & Shi (2021) and Kimmerl, Mertes & Abdel-Maksoud (2021). In particular, Stark & Shi (2021) analysed the acoustic signature of four-bladed ducted thrusters, using data from improved delayed detached-eddy simulation (IDDES), conducted on an unstructured hexahedral mesh consisting of about 13 million elements.…”

“…The porous approach was recently pursued by Stark & Shi (2021) and Kimmerl, Mertes & Abdel-Maksoud (2021). In particular, Stark & Shi (2021) analysed the acoustic signature of four-bladed ducted thrusters, using data from improved delayed detached-eddy simulation (IDDES), conducted on an unstructured hexahedral mesh consisting of about 13 million elements. Implicit LES on grids composed of O(10 7 ) volumes was utilised by Kimmerl et al (2021) to study the Newcastle propeller and the P1595 test case.…”

Marine Ducted Thruster Underwater Radiated Noise Control Through Leading-Edge Tubercle Blade Modifications - a Numerical Hybrid Approach

“…This ability is aided by the small bumps or leading-edge (LE) tubercles located on the pectoral fins of the mammal [7]. LE tubercles have been researched on applications such as aero/hydrofoils, tidal turbines, rudders and marine propulsors [8][9][10][11][12][13][14][15][16]. LE tubercles produce counter-rotating vortex pairs which can influence the local flow-field, and the tubercle modifications have shown to alter the cavitation development on a variety of applications.…”

“…The investigation showed that cavitation can be contained and URN levels can be reduced in certain operating conditions. More recently, LE tubercles have been applied to open and ducted propellers blades, as well as the duct [12][13][14][15][16]. Using CFD, Stark and Shi [13] showed that tubercle modified marine propellers could enhance hydrodynamic efficiency under heavycavitating conditions while the tubercles induced a cavitating fencing pattern, confining the sheet cavitation to behind the trough regions which resulted in a reduction in cavitation volume.…”