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In Europe, the routes of most watercourses were straightened and shortened, leading to the destruction and degradation of many natural environments. Currently, in places where it is possible, as part of the implementation of the Water Framework Directive, efforts are made to improve environmental sustainability, including improving the ecological condition of rivers. This paper presents the impact of three in-stream deflectors on changes in the section of a small lowland river—the Flinta (Poland)—where (from 2018 to 2023) detailed, systematic geodetic, and hydrometric research and an assessment of the ecological conditions were carried out. The presented results show the influence of deflectors on the initiation of fluvial processes in the transverse and longitudinal layouts of the channel. The river channel was narrowed from 6 to 5 m, and the current line shifted by almost 3 m. Changes were observed in the distribution of velocities and shear stresses, varying along the surveyed section of the river. In the first year after their application, an increase in velocity at the deflectors can be observed (from 0.2 m∙s−1 to 0.6 m∙s−1 in the deflector cross-section). In the following years, on the other hand, a clear decrease in velocity was observed in the sections between the deflectors (to 0.3 m∙s−1). The introduction of deflectors resulted in a significant increase in the values of shear stresses (from an average value of 0.0241 N∙m−2 in 2018 to 0.2761 N∙m−2 in 2023) and local roughness coefficients (from 0.045 s∙m−1/3 before the introduction of the deflectors to 0.070 s∙m−1/3 in 2023). Based on analyses of sediment samples, erosion and accumulation of bottom material were initially observed, followed by a subsequent stabilisation of particle size. Differences in grain size were observed, especially in the cross-section of the deflectors (increase in granularity d50% downstream of the deflector from 0.31 mm to 3.9 mm already 2 years after the introduction of deflectors). This study confirmed the positive impact of using deflectors on hydromorphological processes as deflectors facilitate the achievement of a good ecological status, as required by the WFD. The innovation of this paper lies in demonstrating the possibility of using small, simple structures to initiate and intensify fluvial processes, which may contribute to improving the ecological conditions of watercourses. [ABSTRACT FROM AUTHOR]

The resistance loss and energy consumption when fluid flows through a tee in an HVAC system are severe. To improve energy efficiency and reduce carbon emissions, a novel tee with a U-shaped deflector is proposed, supported by experiments and numerical simulations. The resistance reduction mechanism of the U-shaped deflector was analyzed according to the viscous dissipation principle and the field synergy principle. The resistance reduction of the novel tee with different deflector angles and a traditional tee were compared. The results show that the resistance loss of the tee was mainly due to the flow separation and deformation of the fluid in the main branch. The relationship between the local resistance coefficient and the diameter ratio of the main-branch pipe was exponential, and the relationship between the local resistance coefficient and the diameter ratio of the main straight pipe was linear. The total resistance loss reduction rate of the tee with the addition of a 26° deflector was the highest, reaching 72.4%, the volume-weighted average synergy angle increased by 1°, and the viscous dissipation decreased by 21.7%. This study provides a reference for the resistance reduction design of complex local components such as tees in HVAC systems. [ABSTRACT FROM AUTHOR]

The unsteady RANS equations for a two-dimensional hydrofoil were solved using ANSYS Fluent to model and simulate the hydrofoil at a constant Reynolds number, Re, of 2 × 105 and a fixed reduced frequency, f*, of 0.14. The simulations were performed by varying parameters, such as the number of deflectors N, tilt angle of the deflectors β, and vertical spacing of the deflectors J* = J/c, to determine the effect of the upstream deflector's position on the hydrofoil's performance. The results demonstrated that the deflector was effective at redirecting the separated flow away from the edges, which was then amplified downstream before colliding with the leading edge of the oscillating hydrofoil to increase power extraction. The performance of the oscillating hydrofoil was highly reliant on all three studied parameters. The hydrofoil with two deflectors (N = 2) displayed marginally superior power extraction capability compared to the hydrofoil with a single deflector (N = 1). Furthermore, the hydrofoil with the rightward inclined deflector at a low tilt angle (−5° ≥ β ≥ −10°) exhibited relatively better power extraction performance than the others. The best deflector design increased the hydrofoil's cycle-averaged power coefficient by approximately 32% compared to a hydrofoil without a deflector. The vortex structures revealed that the flow evolution and power extraction performance were dependent on the size, robustness, and growth rate of the leading edge vortex (LEV) as well as the timing of LEV separation. The power extraction efficiency of an oscillating hydrofoil increased in the mid downstroke and upstroke due to the formation of a more robust LEV when the hydrofoil–deflector interaction was advantageous, but it dropped in the wing reversal due to the early separation of the LEV when the hydrofoil–deflector interaction was counterproductive. [ABSTRACT FROM AUTHOR]

Highly modified riverbeds are not able to spontaneously reproduce natural processes. The restoration of natural river systems is an important challenge to modern river engineering. Various procedures and solutions, both technical and non-technical, are applied in this process. This involves looking for simple solutions that are close to nature and that interfere with river ecosystems to a minimal extent. One of these solutions is deflectors, which constitute a type of simplified spur. This study presents the results of the research on the transformations of hydromorphology and macrophytes on selected sections of the Flinta River, which represents the most common type of river in the Central European Lowlands (a small river with a sandy substrate). Two neighbouring sections of the watercourse were selected. The first one has not been subject to any regulatory measures for over 30 years and is undergoing spontaneous restoration, while the second one was significantly altered (straightened, cleared of hydrophytes, and desilted) ten years ago. Three deflectors were introduced in this section in the years 2017–2018. Research conducted on both sections enabled the determination of the possibility of initiating renaturalisation processes by way of implementing simple solutions in the form of low-cost wooden deflectors. It also provided the basis for the assessment of the impact the measures taken had on the hydromorphological status of the watercourse and on macrophytes. Based on the studies conducted, it was possible to determine the size, dynamic, and scope of the changes taking place in the river under various conditions of its transformation, including those resulting from anthropopressure. [ABSTRACT FROM AUTHOR]

Spray strips are deflectors added to the hull to reduce the Wetted Surface Area (WSA). The reduced WSA will decrease the total ship drag caused by the deflection of the spray strip installation. The research aimed to predict the function of the spray strip to improve ship performance using Computational Fluid Dynamics (CFD). The numerical approach in this study used the Finite Volume Method (FVM) with the RANS (Reynolds-averaged Navier-Stokes) equation to solve fluid dynamics problems. VOF (Volume of Fluid) was used to model the water and air phases. The results of this study indicated that the number of spray strips would have a significant effect compared to without using a spray strip. Spray strips with three strips could reduce the total resistance by 4.9% at Fr 1.78. Spray strips would increase the total resistance value by 2.1% at low speeds. Spray strips were effective for reducing total resistance at Fr > 1 or the planing mode conditions. The total resistance prediction used three suggestion profiles with the best performance to reduce total resistance by 6.0% at Fr 1.78. [ABSTRACT FROM AUTHOR]

Stepped spillways are frequently limited to specific discharges under around 30 m2/s due to concerns about potential cavitation damages. A small air concentration can prevent such damages and the design of bottom aerators is well established for smooth chutes. The purpose of this study is to systematically investigate the performance of a deflector aerator at the beginning of stepped chutes. Six parameters (chute angle, step height, approach flow depth, approach flow Froude number, deflector angle and deflector height) are varied in a physical model. The spatial air concentration distribution downstream of the aerator, the cavity sub-pressure, water discharge and air discharges are measured. The results describe the commonly used air entrainment coefficient, the jet length, as well as the average and bottom air concentration development to design an aerator. The lowest bottom air concentration measured in all tests is higher than the air concentration recommended in literature to protect against cavitation damages. And, unlike smooth chutes, there appears to be no significant air detrainment downstream of the jet impact. One deflector aerator seems therefore sufficient to provide protection of a stepped spillway. [ABSTRACT FROM AUTHOR]

The deflector and the rod bank are commonly used to optimize flue gas distribution in the original spray tower (OST) of a wet flue gas desulfurization system (WFGD). In this paper, the internal optimization mechanism of the deflector desulfurization spray tower (DST) and the rod bank desulfurization spray tower (RBST) are studied. Based on the Euler–Lagrange method, the standard k-ε turbulence model, an SO2 absorption model and a porous media model, the numerical simulation of the desulfurization spray tower is carried out with the verification of the model rationality. The results show that there are gas-liquid contact intensification effects in DST and RBST. Compared with OST, gas-liquid contact intensification enhances the heat and mass transfer effects of DST and RBST. The temperature difference between inlet and outlet of flue gas increased by 3.3 K and the desulfurization efficiency of DST increased by 1.8%; the pressure drop decreased by 37 Pa. In RBST, the temperature difference between the flue gas inlet and outlet increased by 5.3 K and the desulfurization efficiency increased by 3.6%; the pressure drop increased by 33 Pa. [ABSTRACT FROM AUTHOR]

Marine current power is a kind of renewable energy that has attracted increasing attention because of its abundant reserves, high predictability, and consistency. A marine current turbine is a large rotating device that converts the kinetic energy of the marine current into mechanical energy. As a straight-bladed vertical axis marine current turbine (VAMCT) has a square or rectangular cross-section, it can thus have a larger swept area than that of horizontal axis marine current turbines (HAMCT) for a given diameter, and also have good adaptability in shallow water where the turbine size is limited by both width and depth of a channel. However, the low energy utilization efficiency of the VAMCT is the main bottleneck that restricts its application. In this paper, two-dimensional numerical simulations were performed to investigate the effectiveness of an upstream deflector on improving performance of the straight-bladed (H-type) marine current turbine. The effects of various key geometrical parameters of the deflector including position, length, and installation angle on the hydrodynamic characteristics of the VAMCT were then systematically analyzed in order to explore the mechanism underlying the interaction between the deflector and rotor of a VAMCT. As a result, the optimal combination of geometrical parameters of the deflector by which the maximum energy utilization efficiency was achieved was a 13.37% increment compared to that of the original VAMCT. The results of this work show the feasibility of the deflector as a potential choice for improving the energy harvesting performance of a VAMCT with simple structure and easy implementation. [ABSTRACT FROM AUTHOR]

In this paper, a Janus metasurface is designed by breaking the structural symmetry based on the polarization selection property of subwavelength grating. The structure comprises three layers: a top layer having a metallic nanostructure, a dielectric spacer, and a bottom layer having subwavelength grating. For a forward incidence, the metal-insulator-metal (MIM) structure operates as a gap plasmonic cavity if the linearly polarized (LP) component is parallel to the grating wires. It also acts as a high-efficiency dual-layer grating polarizer for the orthogonal LP component. For the backward incidence, the high reflectance of the grating blocks the function of the gap plasmonic cavity, leading to its pure functioning as a polarizer. A bifunctional Janus metasurface for 45 degrees beam deflector and polarizer, with a transmission of 0.87 and extinction ratio of 3840, is designed at 1.55 μm and is investigated to prove the validity of the proposed strategy. Moreover, the proposed metasurface can be cascaded to achieve more flexible functions since these functions are independent in terms of operational mechanism and structural parameters. A trifunctional Janus metasurface that acts as a focusing lens, as a reflector, and as a polarizer is designed based on this strategy. The proposed metasurface and the design strategy provide convenience and flexibility in the design of multifunctional, miniaturized, and integrated optical components for polarization-related analysis and for detection systems. [ABSTRACT FROM AUTHOR]

Several different designs and prototypes of ocean current turbines have been tested over recent years. For every design test, emphasis is given to achieving an optimum power output from the flow. In this study, the performance of a Horizontal Axis Ocean Current Turbine (HAOCT) has been investigated using three-dimensional Computational Fluid Dynamics (CFD) simulations for three cases, namely, (1) a turbine without a deflector, (2) a turbine with a deflector, and (3) a turbine with a deflector operating at a higher fluid depth. The turbine design was modeled in DesignModeler software and simulations were carried out in commercial CFD software Flow-3D. The Torque Coefficient (Cm) and Power Coefficient (Cp) for the turbine have been investigated for a certain range of Tip-Speed Ratios (TSRs) in a flow velocity of 0.7 m/s. Furthermore, comparisons have been made to demonstrate the effect of the deflector on the performance of the turbine and the influence of a higher fluid pressure on the same. The results from the simulations indicate that the higher value of Cp was achieved for Case 2 as compared to the other two cases. The findings from the study indicate that the use of the deflector enhances the performance of the turbine. Furthermore, a higher fluid pressure acting on the turbine has a significant effect on its performance. [ABSTRACT FROM AUTHOR]