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This study presents a methodology for applying the three-dimensional actuator disk-RANS technique in modeling tidal energy converters within a regional-scale simulation. Of particular interest are the robustness of the applied momentum source term and its effectiveness in modeling an array of full-sized tidal turbines under realistic hydrodynamic and operational conditions. The Inner Sound region, which is the site of commercial-scale deployment projects of the Pentland Firth in Scotland, is chosen as the study area. While the actuator disk approach had been used in past studies to parameterize the far-wake region of horizontal-axis tidal turbines, details of its three-dimensional implementation have not been thoroughly discussed. Criteria adopted in deciding the array location are presented in this study, along with the actuator disks' detailed setup and constraints. The models are subjected to one operational characteristic that is similar to commercial devices in service to examine the accuracy of the imposed source term under complex flow conditions. The results demonstrate that the thickness of the disk imposed in the source term has a pronounced influence on the model outputs. In addition to accurately modeling flow propagation and wake interactions, the models are also able to replicate the observed asymmetrical tidal currents in the region. Because there is currently limited published material on the detailed application of the actuator disk approach in ocean-scale models, this study is hoped to fill the research gap and provide evidence, guidance, and examples of best practices for future studies. [ABSTRACT FROM AUTHOR]

Abstract The aim of this study is to characterize the steady and unsteady flows of a high‐speed axial fan stage and assess its aerodynamic performance parameters. The flow unsteadiness is related to the stator‐rotor interaction originated mainly by two mechanisms: the first is attributed to the potential effect and the second to the wake‐blade interaction and the mixing through the blades' passages. Such effects are dependent on the circumferential positions of blades and inter‐distance between stator and rotor, which could be alleviated by understanding these flow interactions. The pressure waves' main diametrical modes (two blades interacting with two vanes) and their sequences are predicted analytically. FFT analysis of the computed static pressure fluctuations at different monitor points allowed identifying the prevailing modes of interaction and their frequencies and sequence. The assessment of inter‐distance is an important step toward identifying the detrimental effects of axial interdistance on the aerodynamic performance. The closer the blade‐rows of this fan stage can be spaced, the more compact the cooling system of an automotive could be designed.

The aim of this study is to characterize the steady and unsteady flows of a high‐speed axial fan stage and assess its aerodynamic performance parameters. The flow unsteadiness is related to the stator‐rotor interaction originated mainly by two mechanisms: the first is attributed to the potential effect and the second to the wake‐blade interaction and the mixing through the blades' passages. Such effects are dependent on the circumferential positions of blades and inter‐distance between stator and rotor, which could be alleviated by understanding these flow interactions. The pressure waves' main diametrical modes (two blades interacting with two vanes) and their sequences are predicted analytically. FFT analysis of the computed static pressure fluctuations at different monitor points allowed identifying the prevailing modes of interaction and their frequencies and sequence. The assessment of inter‐distance is an important step toward identifying the detrimental effects of axial interdistance on the aerodynamic performance. The closer the blade‐rows of this fan stage can be spaced, the more compact the cooling system of an automotive could be designed. [ABSTRACT FROM AUTHOR]

Abstract The Wadden Sea is one of the most important stop-over sites for breeding and migrating birds. About 10–12 million birds per year use the area for foraging and consume about 25%–45% of the standing stock of macrozoobenthos. However, little is known about the influence of birds on the entire ecosystem. We conducted ecological network analysis (ENA) on an important bird breeding and resting site, the Norderaue tidal basin in the northern German Wadden Sea, to determine the influence of birds on the entire food web. The model was based on the yearly average biomass of system compartments empirically sampled every season at the study site. The analysis revealed a complex and well-connected food web (high flow diversity and effective link-density) dominated by short pathways but with a high throughput of energy. The system's energy had a high degree of freedom for its development. However, there is a strong dependency on external imports of phytoplankton due to the dominance of suspension feeders suggested by a low recycling and the detritivory to herbivory ratio. A large variety of bird species uses the area for foraging and induces a negative impact on their prey items revealed by the mixed trophic impact analysis. The food sources and also the competitors of the birds' prey items were positively influenced by the birds via indirect pathways in the network. Furthermore, there is a negative impact among the bird compartments probably due to competition between the bird species. A sensitivity analysis, conducted by changing the bird biomass in the model, revealed only small changes in the activity, complexity and connectivity of the system. The linkage to other system components could amplify these changes in the system functioning. It is therefore recommended to include birds in coastal food web studies which has rarely been done before. The use of holistic approaches such as ENA would facilitate decisions on management measures by providing a simplified representation of the entire ecosystem including all direct and indirect connections between the system components. Graphical abstract Image 1 Highlights • The Wadden Sea is an important foraging site for breeding and migrating birds. • Influence of birds on food web scale was assessed using ecological network analysis. • Results reveal close linkage of bird compartments to other system components. • Sensitivity analysis applied by changing the bird biomass in the model revealed constant trends but quantitatively small changes in the system indices. • Holistic approaches could be the basis for improving conservation strategies for the Wadden Sea. • Monitoring strategies need to be developed for including top predators properly. [ABSTRACT FROM AUTHOR]

Highlights: [•] Subsurface drainage modifies flow transfer. [•] During heavy rainfall events drains flow under pressurised conditions. [•] Integrated modelling is a relevant approach to study the drainage behaviour. [•] Pipe pressurisation results in temporary storage of water and delayed release of this water. [•] The model reveals that drain pressurisation is not uniform in the field. [Copyright &y& Elsevier]

Direct numerical simulation has been performed to study flow interactions in multiple jets in cross-flow. Configurations considered are twin jets side-by-side and triple jets in tandem. Computations are carried out at the jet to cross-flow velocity ratio of 2.5 and the Reynolds number 225 based on the free-stream quantities and the jet width D. For twin jets, results show that in the vicinity of jet exits, the merging of two counter rotating vortex pairs (CRVP) is strongly dependent on the gap of two jets. Downstream in the far-field, a large single CRVP dominates. The simulation is in qualitatively good agreement with the experimental findings by other researchers. For triple jets, more complicated flow structures are revealed, in which a total of three vortex pairs has been identified, but none of them is dominating. The observations of complex flow structure could assistant relevant industrial applications. [ABSTRACT FROM AUTHOR]

In this paper, the drag reduction benefits associated with 2 and 3 cars in platoon have been investigated. Following a validation of initial CFD simulations against experimental measurements, predictions of surface pressures and wake structure for alternative platoon configurations have been analysed to determine the changes of flow structure that influence the pressure field and drag force on each vehicle. Contrary to several publications it was found that in a platoon of two vehicles, the drag force of the trailing vehicle exceeded that of an isolated vehicle for close spacings. Analysis of this surprising result revealed that design features introduced to optimise the wake of an isolated vehicle can lead to a drag increase on a following vehicle. For three-vehicle platoons, the flow interaction between the leading and middle vehicles remained largely unchanged but the additional effect of the third vehicle resulted in all three vehicles exhibiting lower drag than that of an isolated vehicle. A clear implication of this work is that results from the analysis of vehicle platoons are likely to be sensitive to the geometry and wake structures of the chosen test vehicle which helps to explain why many previous studies have been seemingly contradictory. Image 1 • Geometrical features optimised for isolated vehicle are detrimental for platoons. • Vertical and lateral stretching of the wake leads to base pressure increase. • The trailing vehicle in a 2-vehicle platoon experiences drag higher than isolation. • All the vehicles in a 3-vehicle platoon show drag reductions. • The leading vehicle in most cases showed the highest drag reduction. [ABSTRACT FROM AUTHOR]