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To meet the increased demand of hydroelectric power generation, a novel drag-based Savonius turbine with the characteristics of a simpler fabrication process and good starting characteristics is designed, fabricated, and analyzed. The newly designed turbine is suitable to be installed in rivers, irrigation channels, ocean currents, etc., for small-scale hydroelectric power generation. In the present study, experiments are carried out to investigate the influence of the design parameters of this turbine on its power performance in order to improve its efficiency, including blade arc angles (180°, 135°), blade placement angles (0°, ±22.5°), and the number of blades (2, 3, 6, and 8). Further, three-dimensional CFD simulations are performed with Re = 6.72×105, matching the experimental conditions, in order to study the changes in the flow field and the rotation characteristics of the turbine. The research results indicate that a six-bladed turbine with a blade arc angle of 135° and a blade placement angle of 0° has higher torque and better power performance, which makes it the most suitable design when also considering cost. Furthermore, it was found that an increase in the number of turbine blades contributes to improving the performance of the turbine. The maximum power coefficient is 0.099 at a tip speed ratio of 0.34.

Savonius-like-hydrokinetic turbine (SLHT) is a revelation for small-scale (micro/pico) power generation from perennial rivers at low water velocities and low tip speed conditions. However, for its operation at such sites, efficiency is to be improved by design modifications and flow control. This work entails a flow control strategy that combines the mean flow with overlapping flow, gap flow between stages, and flow between end plates. Here, the performance of a two-bladed two stage SLHT with end plates and 15% blade overlapping is examined in a water channel with stage gaps in mm (0-20), low water velocities in m/s (0.45-0.65) under applied braking loads in g (100-1500). The results demonstrate that SLHT produces more power and torque under a low-stage gap as the brake load rises, reaching the highest hydrodynamic torque (0.056 Nm) during a maximum load of 1250 g. The minimal stage gap is 5 mm, turbine braking loading 1250 g, 0.248 TSR, and 0.55 m/s water velocity yield the highest power coefficient (0.058), which is greater than some published SLHT designs. Thus, as much as blade profile modifications, flow control through SLHT can be the future direction for further improvement of its performance.

This study aimed to determine the optimal rotor spacing of two vertical-axis wind turbines, which are simulated by miniature models arranged side-by-side with a relatively low aspect ratio. Wind tunnel experiments with a pair of 3-D printed model rotors were conducted at a uniform velocity. A series of experiments were conducted involving both incremental adjustments to the rotor gaps, g, and the rotational direction of each rotor. Increases in the power and the related flow patterns were observed in all three arrangements: Co-Rotating (CO), Counter-Up (CU), and Counter-Down (CD). The maximum phase-synchronized rotational speed occurs at the narrowest gap in the CD arrangement. Meanwhile, local maxima arise in the CO and CU arrangements at g/D < 1, where D is the rotor diameter. From an engineering perspective, the optimal rotor spacing is g/D = 0.2 with the CO arrangement, using the same two rotors rotating in the same direction. Based on flow visualization using a smoke-wire method at a narrower gap opening of 0.2D, the wake width in the case of the CU arrangement was remarkably narrower than those obtained in the CO and CD arrangements. In the CU arrangement, a movement towards the center of the rotor pair of the nominal front-stagnation point of each rotor was confirmed via flow visualization. This finding explains a reduction tendency in the rotational speed of the rotors via a reduction in the lift in the CU arrangement.

In this study, numerical investigations on the energy extraction performance of a flapping foil device are carried out by using a modified foil shape. The new foil shape is designed by combining the thick leading edge of NACA0012 foil and the thin trailing edge of NACA0006 foil. The numerical simulations are based on the solution of the unsteady and incompressible Navier-Stokes equations that govern the fluid flow around the flapping foil. These equations are resolved in a two-dimensional domain with a dynamic mesh technique using the CFD software ANSYS Fluent 16. A User Define Function (UDF) controls the imposed sinusoidal heaving and pitching motions. First, for a validation study, numerical simulations are performed for a NACA0012 foil undergoing imposed heaving and pitching motions at a low Reynolds number. The obtained results are in good agreement with numerical and experimental data available in the literature. Thereafter, the computations are applied for the new foil shape. The influences of the connecting area location between the leading and trailing segments, the Strouhal number and the effective angle of attack on the energy extraction performance are investigated at low Reynolds number (Re = 10 000). Then, the new foil shape performance was compared to those of both NACA0006 and NACA0012 baseline foils. The results have shown that the proposed foil shape achieves higher performance compared to the baseline NACA foils. Moreover, the energy extraction efficiency was improved by 30.60% compared to NACA0006 and by 17.32% compared to NACA0012. The analysis of the flow field around the flapping foils indicates a change of the vortex structure and the pressure distribution near the trailing edge of the combined foil compared to the baseline foils.

This work explores the performance improvement of a Savonius Hydro Turbine (SHT) installed inside a 4-inch pipeline by examining the combined effects of the guide-vane angle and central-shaft opening ratio were assessed through Computational Fluid Dynamics simulations supported by experimental measurements. Five turbine configurations (M5-1 to M5-5) were analyzed with the SST-enhanced k–ω turbulence formulation under guide-vane angles of 0°, 25°, 30°, and 35°. The results revealed that both parameters significantly influence the flow field and turbine efficiency. The central-shaft opening reduces reverse flow and torque reversal acting on the retreating blade, whereas the guide vane channels the incoming stream toward the forward-moving blade. Among all configurations, the M5-3 turbine (30 % opening, 35° guide vane) exhibited the most favorable performance, yielding maximum power coefficient (Cp,max) value of 0.3969 (simulation) and 0.3778 (experiment) at Tip Speed Ratio (TSR) close to 0.59. These represent 233 % and 257 % improvements, respectively, compared with the case without a guide vane (M5-3, 0° guide vane). Compared with the solid-shaft turbine (M5-1, 35° guide vane), Cp increased by 48 % (simulation) and 55 % (experiment). The deviation between simulated and experimental Cp ranged from 5.06 % to 12.38 %, decreasing with increasing guide-vane angle, validating the CFD predictions. The combination of a 30 % central-shaft opening and a 35° guide-vane angle produced the most efficient flow interaction, showing strong potential for low-head, in-pipe hydropower recovery in industrial and municipal pipeline systems.

Wind energy is experiencing a trend of exponential growth in both literature and industrial employment, emphasizing its current pivotal role in achieving carbon neutrality by replacing fossil fuels. Vertical axis wind turbines (VAWTs) particularly Savonius rotors operate at a lower tip-speed-ratio (TSR) range compared to horizontal axis wind turbines (HAWTs). The Savonius rotor has good starting characteristics, making it suitable to be placed in urban areas with lower wind speeds. Due to its low efficiency, studies on augmentation and optimization have been conducted to improve its blade and deflector designs. Extensive research has established a common consensus that the use of endplates significantly improves the aerodynamic performance of the Savonius rotor. However, limited research has been undertaken to explore the endplate design further. In this study, wind tunnel tests were conducted on different endplate ratios, to investigate the effects of endplate design on the aerodynamic performance of a conventional Savonius turbine. Three different Savonius rotor with no endplate, semi-circular endplate and circular endplate were designed and manufactured. Experiments were conducted in an open-type suction wind tunnel at a constant measured wind velocity of 5.89 m/s. The turbine’s performance for different endplate ratios was evaluated across a TSR range of 0.2 to 1.0. The performance was assessed based on the maximum power generated and its self-starting ability. From the experimental results, the circular endplate ratio of 1.1 shows a significantly high coefficient of power compared to both semi-circular and without endplates. This is due to reduced spanwise spillage and enhanced airflow capture by the rotor. The endplates direct incoming air to the advancing blade and overlap region, resulting in the increased pressure difference between the concave and convex sides of both the advancing and returning blade, thereby improving the power efficiency of the turbine with 1.1D diameter endplate and semi-circular endplate by 296.6% and 6.9% compared to no endplates case.

In our latest research, we investigated the incorporation of an undulatory pattern along the concave surface of Savonius turbine blades. This study builds upon our previous findings, where we examined the effects of varying undulation counts across four distinct shapes (with radius of 22 mm, 30 mm, 60 mm, and 80 mm), while maintaining consistent overall blade dimensions. To analyze the aerodynamic performance, we employed the unsteady Reynolds-Averaged Navier-Stokes (RANS) equations in conjunction with the Shear Stress Transport (SST) k-ω turbulence model, using ANSYS Fluent software. In the current study, the number of undulations was increased by approximately 50%, resulting in a total of 60 points along the blade profile. This enhanced configuration was validated using recent numerical data to assess its impact on the moment and power coefficients of the turbine across a range of tip speed ratios (TSRs). All simulations were conducted under consistent conditions, including a 15% overlap ratio relative to the rotor diameter and an inlet wind velocity of 7 m/s. This study shows that the MODEL80 exhibited the highest power coefficient value of 0.277.

This paper presents a review of the power and torque coefficients of various wind generation systems, which involve the real characteristics of the wind turbine as a function of the generated power. The coefficients are described by mathematical functions that depend on the trip speed ratio and blade pitch angle of the wind turbines. These mathematical functions are based on polynomial, sinusoidal, and exponential equations. Once the mathematical functions have been described, an analysis of the grouped coefficients according to their function is performed with the purpose of considering the variations in the trip speed ratio for all the coefficients based on sinusoidal and exponential functions, and with the variations in the blade pitch angle. This analysis allows us to determine the different coefficients of power and torque used in wind generation systems, with the objective of developing algorithms for searching for the point of maximum power generated and for the active control of wind turbines with variations in the blade pitch angle.

The application of vertical axis wind turbines (VAWTs) is gaining increasing attention, particularly in urban areas with highly turbulent wind conditions. The airfoil blade is a critical component of a wind turbine which determines its overall performance. However, Darrieus turbines often suffer from self-starting issues which are closely related to inertia. Since blade inertia is influenced by their material, lightweight materials are typically used for blade manufacture. Nevertheless, experimental study on the blade inertia of VAWTs remain limited. This paper investigates the effects of blade inertia on a straight-bladed VAWT. A two-bladed NACA0018 VAWT with a 700 mm diameter and an aspect ratio of 1 was fabricated and tested in a wind tunnel at an incoming wind speed of 5.61 m/s. To compare the effects of inertia, two different blade coatings—epoxy and thin film were used. The difference in the coating material density resulted in varying blade inertia. The study focused on self-starting behavior, maximum rotational speed, and power output. The coefficient of power ( C P ) was analyzed across a wide range of tip speed ratios (TSRs) under various load conditions. The results indicate that as inertia increases, the turbine takes longer to reach its maximum rotational speed, exhibiting lower angular acceleration and greater fluctuation in the transient state before stabilizing. Additionally, the VAWT with 2.3 times higher blade inertia exhibited lower maximum rotational speed and power output. In contrast, the turbine with lower blade inertia achieved a 30% higher rotational speed and a 69.75% increase in maximum C P .