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The impact of two tubercle leading-edge (TLE) modifications on the turbulent wake of a reference marine rudder at Reynolds number 2.26 × 106 was analysed numerically using Detached Eddy Simulations (DES). This paper studies the counter-rotating vortex pair formation around the TLE and their impact on the wake structures behind the rudder to find out if the vortex interaction can accelerate the tip vortex dissipation. According to the results, the tubercles enhanced lift for angles of attack (AOA) 10º and above, but at the cost of a drag penalty which reduced the rudders’ lift-to-drag ratio. The formation of the distinctive stream-wise counter-rotating vortex pairs occurred behind the tubercles, which then interacted with the dominant tip vortex. Due to the inherent spanwise flow component of finite-span lifting surfaces the counter-rotating vortex pairs were generated at unequal strength and soon merged into singular vortices co-rotating with the tip vortex. The vortices facilitated flow compartmentalisation over the rudder suction side which broke up the trailing-edge vortex sheet and confined the spanwise flow separation over the rudder surface as AOA increased. The tubercles confined flow separation closer to the rudder tip which reduced the lift generation in the tip area and minimised the initial tip vortex strength. Large elements of stream-wise counter-rotating vorticity formed around the localised stall cells of the TLE rudders that interacted with the tip vortex downstream, introducing elliptical instabilities further weakening the tip vortex and changing its trajectory.

Leading edge tubercles (LET) is an attractive passive flow control solution that has been proved to enhance the hydrodynamic performance and efficiency of lifting surfaces adopted in many engineering areas. Nonetheless, their industrial application in control and propulsion devices of marine vehicles is still at the beginning. To move further steps ahead, a preliminary experimental campaign for a five bladed Wageningen B-screw propeller modified with three different configurations of leading edge tubercles was carried out in cavitation free conditions. In particular, the propellers were tested in open water conditions in straight and oblique flow at incidences of 10° and 20°, with the aim to study the effects of LET during steady and moderate unsteady conditions. The propellers are tested at two different chord Reynolds numbers in order to investigate their applicability also to small autonomous marine vehicles. The analysis proved that suitable layout of tubercles can enhance the hydrodynamic efficiency in axial symmetric flow while reducing undesired effects caused by operation in off-design.

The impact of two tubercle leading-edge (TLE) modifications on the turbulent wake of a representative marine rudder at Reynolds number 2.26×106 was analysed numerically using Detached-Eddy Simulations. TLE have been shown to alter the flow profile over aero/hydrofoils through the generation of streamwise counter-rotating vortex pairs behind the tubercles, which can enhance the lifting performance. This paper studies the formation of these vortex pairs and their impact on the wake structures behind the rudder to find out if vortex interaction can reduce the tip vortex. The tubercles enhanced lift for angles of attack (AOA) 10º and above, but at the cost of a large drag penalty that reduced the rudders' lift-to-drag ratio. The formation of the distinctive streamwise counter-rotating vortex pairs behind the tubercles was shown. Due to the inherent spanwise flow component of finite-span lifting surfaces the vortices were generated at unequal strength and only positive vortices were maintained in the wake. The vortices facilitated flow compartmentalisation over the rudder suction side which broke up the trailing-edge vortex sheet and confined the spanwise flow separation over the rudder surface as AOA increased. The tubercles confined flow separation closer to the rudder tip which caused a tip-offloading effect that minimised the initial tip vortex strength. Large elements of streamwise counter-rotating vorticity formed around the localised stall cells of the TLE rudders that interacted with the tip vortex downstream, introducing elliptical instabilities further weakening the tip vortex and changing its trajectory.

Cavitation is an ever-present issue in the maritime industry as it causes damage to the propeller in the form of erosion, reducing hydrodynamic performance and increasing the underwater radiated noise (URN) level generated. Therefore, containing cavitation on marine propellers is an important area to research in order to reduce structural damage, efficiency loss and noise pollution. Recently there has been growing research in the leading-edge (LE) tubercles located on Humpback whale pectoral fins that have been attributed to give the whales superior manoeuvrability through prolonged flow attachment and have shown to improve hydrodynamic performance on marine applications. This paper assesses the sheet cavitation containment capability of the LE tubercles on a benchmark ducted propeller blade in both heavy and light cavitating conditions. The analysis is carried out over a range of operating conditions using commercial code STAR-CCM+ with the implicit unsteady Improved Delayed Detached Eddy Simulation (IDDES) method and the Schnerr-Sauer cavitation model. The investigation encompassed two tubercle designs with varying geometrical configurations of wavelength while maintaining the amplitude. In summary, it was found that LE tubercles as applied to the Kaplan propeller blade has presented a cavitation funnel effect which can successfully reduce the sheet cavitation development by a maximum of 50%, while enhancing the total thrust coefficient in all operating conditions by a maximum of 10%. Comparing at the same thrust loading coefficient, the propulsive efficiency in heavy-cavitating conditions can be improved by a maximum of 6.5%.

Marine ducted thrusters are widely used to provide propulsive thrust for a range of marine vessels due to their high thrust capability in heavy loaded conditions. This paper presents a novel and optimised bio-inspired marine ducted thruster, where leading-edge tubercles are applied to the duct of a ducted propulsor to explore the impact on hydrodynamic performance. Nine different geometrical configurations of tubercle were investigated with varying amplitude and wavelength within the optimisation study. The hydrodynamic performance of the marine ducted thruster is evaluated using a commercially available computational fluid dynamics (CFD) code, STAR-CCM+, with an incompressible implicit unsteady Reynolds-Averaged Navier Stokes (RANS) solver combined with the Body Force Propeller (BFP) method for the duct optimisation study. Then, the selected optimal duct was chosen for further analysis using the propeller resolved Rigid Body Motion (RBM) method, more commonly known as the sliding mesh technique. Through the numerical optimisation study, the leading-edge modification is predicted to have the capability to enhance the duct thrust in the heavy-loaded conditions, although this is dependent on the wavelength and amplitude of the tubercle. Furthermore, during the investigation the traditional tubercle behaviour was observed, namely the high-low pressure patterns and streamwise counter-rotating vortices. Interestingly, flow separation was observed to be compartmentalised on the outer side of the duct cross-section in conditions where flow separation occurred such as at the maximum efficiency operating point.

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.

To improve the cost-effectiveness and safety of offshore operations, autonomous underwater vehicles (AUVs) are widely used in various fields. However, traditional docking or recovery methods for AUV’s can be very inefficient as they require the mother vehicle to be stationary. Therefore, to reduce recovery operation cost, shorten the redeployment time and increase operational efficiency when compared to traditional docking methods, the development of underwater dynamic recovery systems for AUVs is critical. Recently the ‘hitchhiking’ behavior of remoras which have a symbiotic relationship with sharks has been investigated, and the numerical results showed that the boundary layers and adverse pressure gradient regions around the shark can provide a significant drag reduction on the remora when it attaches to the shark. To support the feasibility study of the underwater dynamic recovery system of AUVs, this paper develops a remora-like AUV and investigates the potential docking locations on a benchmark submarine, using the commercial computational fluid dynamics (CFD) software, STAR-CCM+. Self-propulsion simulations are conducted to identify the resistance performance of the AUV in different locations as affected by flow around the submarine. The boundary layer and the adverse pressure gradient are the two key elements that affected the AUV resistance. By researching the hydrodynamic characteristics, an optimal docking area is identified and presented to be further researched to fully enable this advanced dynamic docking operation.

Cavitation is an undesirable phenomenon in the maritime industry as it causes damage to the propeller, degrading hydrodynamic performance and increasing the subsequent underwater radiated noise (URN). Therefore, mitigating cavitation on marine propellers is an important area of research in order to reduce carbon emissions emitted from the shipping industry and reduce the rate at which ocean ambient noise levels are increasing. The Humpback whale has provided inspiration to research in the fluid-structure interaction field due to the presence of leading-edge (LE) tubercles on the pectoral fins that allow it to perform acrobatic maneuvers to catch prey. This paper assesses the cavitation containment capability of the LE tubercles on a benchmark marine propeller in both heavy and light cavitating conditions using commercial code STAR-CCM+, unsteady incompressible Reynolds-averaged Navier Stokes (RANS) solver and the Schnerr-Sauer cavitation model to quantify the sheet cavitation present over a range of operating conditions. In summary, in heavy-cavitating conditions, a reduction in sheet cavitation with the inclusion of LE tubercles was observed to a maximum value of 2.75% in all operating conditions considered. A maximum improvement of 3.51% and 1.07% was predicted in propulsive thrust and hydrodynamic efficiency, respectively. In light cavitating conditions, although in some conditions a reduction in cavity volume was observed, this did not result in an improvement in hydrodynamic performance.

This paper presents the sea trials results by measuring the underwater radiated noise (URN) levels of a research vessel retrofitted with the novel "PressurePoresTM" URN mitigation technology on her propellers to demonstrate the effectiveness of this technology in full-scale. Tip Vortex Cavitation (TVC) is one of the main contributors to a URN. So the strategic implementation of the PressurePoresTM is aimed to reduce the TVC and subsequent URN of ship propellers. During the sea-trials, the URN levels were measured when the vessel's propellers were in the unmodified (without PressurePores) and modified (with PressurePores) conditions, including comprehensive cavitation observations using a high-speed camera to assess PressurePoresTM technology. The trial results showed this innovative technology could mitigate the TVC and resulting URN signature by 10dB. Also, in this measurement campaign, a novel URN measurement method using an aerial drone with a miniature hydrophone called the "HyDroneTM" system was tried successfully. HyDroneTM can be a flexible and practical alternative URN measurement technique to the conventional tethered-based method to improve the undesirable background noise corrections.

This study implements leading-edge (LE) tubercles on a benchmark 19A accelerating duct to investigate the impact on the hydrodynamic performance and propeller wake flow development at multiple operating conditions. The study was conducted using Computational Fluid Dynamics (CFD) where the sliding mesh technique was used to describe the propeller rotation and the hydrodynamic flow-field was solved using Improved Delayed Detached Eddy Simulations (IDDES). In summary, it was found that LE tubercles can enhance the thrust of the duct by a maximum of 7.15% and disrupt the coherent vortex structure of the benchmark ducted propeller which will likely influence the noise signature of the propulsor.

The addition of a trailing edge flap is an effective way to enhance the lift generated by marine rudders. This is achieved through camber being introduced into the foil section when the flap is deflected. But the strong curvature in the flow around the flap’s leading edge makes it prone to early flow separation and increased drag. Leading-edge tubercles offer a means to control flow separation whilst improving lifting performance at post-stall angles of attack (AOA). Therefore, this study aims to investigate the tubercle leading edge’s (TLE) ability to improve the hydrodynamic performance of a flapped rudder. A finite-span reference rudder with a 20% trailing-edge flap and its TLE modification were numerically analysed using Detached Eddy Simulations (DES) for fully turbulent flow at a Reynolds number of 1.15 × 106. Flow separation severity and progression were controlled and minimised through the TLE modifications. As a result, the TLE rudder produced up to 15% higher maximum lift and up to 25% more post-stall lift. The rudder efficiency also improved for various rudder and flap angle combinations.