The influence of leading-edge tubercles on the sheet cavitation development of a benchmark marine propeller

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 STARCCM+, 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

The influence of leading-edge tubercles on the hydrodynamic performance and propeller wake flow development of a ducted propeller

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 influence of leading-edge tubercles on wake flow dynamics of a marine rudder

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

Vortex dynamics impact on the wake flow of a marine rudder with leading-edge tubercles

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

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

Study on applicability of energy-saving devices to hydrogen fuel cell-powered ships

The decarbonisation of waterborne transport is arguably the biggest challenge faced by the maritime industry presently. By 2050, the International Maritime Organization (IMO) aims to reduce greenhouse gas emissions from the shipping industry by 50% compared to 2008, with a vision to phase out fossil fuels by the end of the century as a matter of urgency. To meet such targets, action must be taken immediately to address the barriers to adopt the various clean shipping options currently at different technological maturity levels. Green hydrogen as an alternative fuel presents an attractive solution to meet future targets from international bodies and is seen as a viable contributor within a future clean shipping vision. The cost of hydrogen fuel—in the short-term at least—is higher compared to conventional fuel; therefore, energy-saving devices (ESDs) for ships are more important than ever, as implementation of rules and regulations restrict the use of fossil fuels while promoting zero-emission technology. However, existing and emerging ESDs in standalone/combination for traditional fossil fuel driven vessels have not been researched to assess their compatibility for hydrogen-powered ships, which present new challenges and considerations within their design and operation. Therefore, this review aims to bridge that gap by firstly identifying the new challenges that a hydrogen-powered propulsion system brings forth and then reviewing the quantitative energy saving capability and qualitive additional benefits of individual existing and emerging ESDs in standalone and combination, with recommendations for the most applicable ESD combinations with hydrogen-powered waterborne transport presented to maximise energy saving and minimise the negative impact on the propulsion system components. In summary, the most compatible combination ESDs for hydrogen will depend largely on factors such as vessel types, routes, propulsion, operation, etc. However, the mitigation of load fluctuations commonly encountered during a vessels operation was viewed to be a primary area of interest as it can have a negative impact on hydrogen propulsion system components such as the fuel cell; therefore, the ESD combination that can maximise energy savings as well as minimise the fluctuating loads experienced would be viewed as the most compatible with hydrogen-powered waterborne transport

Young Edinburgh Action presents..... YEA, WE CAN!

The creation of this briefing paper was a collaborative project between a group of young people from YEA and an MSc Childhood Studies student from the University of Edinburgh as part of a placement based dissertation. Keeping in the spirit of YEA, to create this briefing paper we used this opportunity to create a questionnaire to find out about how young people who participate in YEA projects feel about their participation. The questionnaires were sent out to all former and active members of YEA and we used the responses to inform this briefing paper

Underwater noise measurements with a ship retrofitted with PressurePoresTM noise mitigation technology and using HyDroneTM system

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

Search for dark matter produced in association with bottom or top quarks in √s = 13 TeV pp collisions with the ATLAS detector

A search for weakly interacting massive particle dark matter produced in association with bottom or top quarks is presented. Final states containing third-generation quarks and miss- ing transverse momentum are considered. The analysis uses 36.1 fb−1 of proton–proton collision data recorded by the ATLAS experiment at √s = 13 TeV in 2015 and 2016. No significant excess of events above the estimated backgrounds is observed. The results are in- terpreted in the framework of simplified models of spin-0 dark-matter mediators. For colour- neutral spin-0 mediators produced in association with top quarks and decaying into a pair of dark-matter particles, mediator masses below 50 GeV are excluded assuming a dark-matter candidate mass of 1 GeV and unitary couplings. For scalar and pseudoscalar mediators produced in association with bottom quarks, the search sets limits on the production cross- section of 300 times the predicted rate for mediators with masses between 10 and 50 GeV and assuming a dark-matter mass of 1 GeV and unitary coupling. Constraints on colour- charged scalar simplified models are also presented. Assuming a dark-matter particle mass of 35 GeV, mediator particles with mass below 1.1 TeV are excluded for couplings yielding a dark-matter relic density consistent with measurements