Higher Power Coefficient Research Articles

Performance assessment of Savonius wind turbine: Impact of the cylindrical deflectors with natural shapes

Savonius wind turbine, with various advantage features, is expanding its application for energy harvesting in urban and offshore environments. However, the drawback of this turbine relies on its relatively low aerodynamic efficiency. This study aims to enhance the Savonius wind turbine's aerodynamic performance to expand its effective application in urban areas and reduce offshore wind energy costs by using multiple cylindrical deflectors with natural geometry, changing from square to circular shapes. Results from the sequence of two-dimensional (2D) unsteady computational fluid dynamics (CFD) simulations show various performances gained depending on the deflector shapes. The highest power coefficient, with an increment of up to 133% over the turbine without the deflectors without the complex structure and the requirement of the rotated cylinder, is attained with the square cylindrical one at different wind conditions. The insight flow analysis reveals that the high jet flow formed between the turbine and the deflectors is the physical reason behind such improvement, through adding more positive pressure force on the advancing blade while increasing the recovery pressure on the concave side of the returning one. The results suppose the significance of the present study with a simple wind turbine-deflector configuration for high energy harvesting in urban and offshore environments with effective costs.

On the Effect of Current Stabilizer on Dynamics of a Small Hybrid Wind Power Generator

The use of small wind power generators remains quite relevant. In particular, they can be efficient for charging batteries in remote locations where there is no centralized power supply (including in the Arctic, Far East, etc.). They can also be used as part of missions to planets with atmospheres. One of the promising design solutions for a small wind power generator with a vertical axis of rotation is a hybrid device. It consists of two wind turbines that have a common axis of rotation: external (Darrieus wind turbine) and internal (Savonius rotor). This scheme represents a compromise between the relatively high power coefficient of the Darrieus turbine and the good startup characteristics the Savonius rotor. It is known that one of the typical battery charging modes is constant current charging. Here we consider a hybrid installation, the generator of which is connected to a current stabilizer. The load is simulated with an active resistance. It is assumed that the generator is a DC generator. A closed mathematical model of the studied system is constructed. The aerodynamic load is described using the quasi-steady approach. It is assumed that the characteristic time of electrical processes is much smaller than the characteristic time of mechanical processes. The influence of load resistance on the behavior of the system is investigated. It is shown that, under certain conditions, several steady modes (up to five) exist in the system. In this case, at least two of them are attracting. Therefore, the hysteresis of the angular speed of the steady mode is possible when the load resistance changes. It should be noted that in a number of situations, an unstable steady mode (which corresponds to a lower angular speed of the turbine than a stable one) may be preferable (for example, to reduce the load on bearings). In this regard, a resistance control strategy has been proposed to ensure stabilization of the unstable stationary regime.

Wind flow characteristics through shrouded wind turbine using ANSYS

Wind energy is a mature and quick-growing source of energy in many nations. New wind energy technologies must be introduced to increase effectiveness and reduce the cost of wind turbine installation. Wind energy conversion experts believe that shrouded wind turbines are a promising technology that could raise output and efficiency levels. A low-pressure zone is created behind the turbine because of the shroud’s unique structure. As a result, the turbine draws in greater mass flow to produce more power. With the aid of this innovative technology, wind turbines could be used in populated areas where lower wind speeds could be captured. In this study, a comparative analysis has been applied to different designs of shrouded wind turbines to analyze the wind speed, pressure, output power and power coefficient. ANSYS software has been conducted in this paper where the results obtained that the output power could be increased up to 3-4 times compared to the bare wind turbine, also a high-power coefficient could be reached up to 83.1%.

Numerical Study on the Effect of Installing Circular Cylinders in Front of the Returning Blade and Beside the Advancing Blade of the Savonius Wind Turbine

Previous research has proven that placing a disruptive cylinder in front of the Savonius wind turbine’s returning blade can significantly increase the performance of the Savonius turbine. In this study, two-dimensional unsteady simulations with a quadratic pave-type structured mesh showed that the circular cylinder placed in front of the returning blade and next to the advancing blade provides the best performance results at a free flow speed of 5 m/s and a Reynolds number of 100,000. In this study, the comparison with experimental data from another study is utilized. The Savonius turbine is installed with an interfering cylinder in front of the returning blade and next to the advancing blade; the air is tighter on the concave side of the advancing blade. The coefficient pressure difference between the convex and concave sides of the blade increases. The maximum moment is achieved in the turbine with a disturbance cylinder at a configuration distance of S/D 1.4 – Y/D 1.61. The maximum moment coefficient is obtained at the position θ = 15°. The placement of two cylinders with a ratio variation of 0.5 D can significantly influence turbine performance. Results show the turbine provides the highest Power Coefficient when TSR = 0.6. The power coefficient increased by 25.11% compared with that of conventional Savonius turbines. Therefore, it can be concluded that the turbine is the optimal configuration for generating the highest power.

Energy Conversion by Helical Hydrokinetic Turbine in A Pipe

Hydrokinetic turbines are mechanisms designed for the purpose of utilizing the kinetic energy present in the movement of water bodies like rivers, tidal currents, or ocean currents, and transforming it into electrical power. These turbines function based on a principle akin to that of wind turbines; however, they are positioned underwater to harness the energy of the water flow. This study focuses on the fundamentals of hydrokinetic turbines and presents existing research. Additionally, simulations have been conducted to observe how the hydrokinetic turbine responds hydrodynamically inside a pipe. A three-bladed vertical-axis helical hydrokinetic turbine was installed within a circular conduit and subjected to analysis under varying flow conditions. The k-ω SST turbulence model was employed in the analyses. The results indicated that increasing the turbine's angular velocity initially raises the torque and the power coefficient until a peak is reached, after which the power coefficient decreases. The highest power coefficient was observed at a flow velocity of 2 m/s. Additionally, consistent with previous studies, the hydrokinetic turbine within the pipe surpassed the Betz limit.

The Effect of Deflector Angle on the Performance of Turbine Combination Darrieus-Savonius

The Savonius and Darrieus are vertical-axis wind turbines. This turbine has resistance on one side of the blade that makes it difficult for the shaft to rotate resulting in reduced efficiency. However, the vertical shaft turbine type provides the advantage of being able to accept wind speeds from any direction without an additional tail. Savonius and Darrieus turbines show different characteristics in terms of their performances. Savonius turbine has a high power coefficient (CP) in the range of low tip speed ratio (TSR), when its TSR increases the CP will fall. In contrast to Darrieus, high CP is achieved if the TSR is also high but the CP achievement will fall at a low TSR. If it is compared to Savonius, Darrieus has higher power efficiency although it is difficult to self-start. In contrast to Savonius, Darrieus has a better self-starting ability but a lower efficiency. This study aims to improve the performance of vertical shaft wind turbines by creating a new design combination of Darrieus and Savonius turbines with deflectors to produce CP achievement on a wide TSR. The combination of the Darrieus-Savonius turbine is to improve efficiency to make self-start easier. The research method uses numerical simulation by employing CFD Ansys software. On the airfoil with a deflector angle of 70 deg, it shows that there is an increase in speed in several parts of the Darrieus blade airfoil. The increase in speed causes the decrease of static pressure in the area. The pressure difference between the sides of the airfoil surface causes a force. The direction of the force causes the turbine shaft to rotate. The deflector acts as a directional headwind, increasing the local flow velocity to counter the resistance on one side of the rotor blades The average torque produced at an angle of 70 deg is 0.5 Nm. Whereas, at an angle of 90 deg, the average torque generated is lower by around 0.15 Nm.

Effect of number of blades on performance and wake recovery for a vertical axis helical hydrokinetic turbine

Hydrokinetic turbine provides a viable option for tapping energy from free-flowing water, making it an attractive contributor to the renewable power landscape. This study investigates the effects of blade number and solidity on the performance and wake recovery of a small-scale vertical axis helical hydrokinetic turbine under different tip speed ratios and inflow velocities. Computational fluid dynamics simulations are employed, followed by experimental validation, to analyze power, self-start, torque pulsations, velocity deficit and flow field characteristics. The highest power coefficient is found to be 0.24 for a 4-bladed rotor with 0.3 solidity at a tip speed ratio of 1.0 and inflow velocity of 1.0 m/s. The performance of the studied rotors decreases as inflow velocity increases due to high turbulence experienced, resulting in flow separation. The self-start characteristics are shown to improve with solidity, while torque pulsations are greatly diminished with the increase in number of blades. The wake analysis results show that the velocity deficit and turbulence intensity increase significantly as the number of blades increases. Moreover, the time-averaged streamwise velocity values are observed to reach almost 95 % at a downstream distance of 19–25 times the rotor diameter for investigated rotors.

A deep learning approach for hydrofoil optimization of tidal turbines

Hydrofoil optimization plays a crucial role in improving the hydrodynamic performance of tidal turbines. However, the high-dimensional representations in hydrofoil design space require significant Computational Fluid Dynamics (CFD) simulations, increasing computational load and time expenditure. This paper proposes a hydrofoil optimization framework based on deep learning to achieve an effective mapping between design parameters, pressure fields, and hydrodynamic characteristics. The designed hydrofoil represented using the Signed Distance Function (SDF) is input to Convolutional Neural Networks (CNN) for fast prediction of hydrodynamic coefficients and pressure field. Due to the effective integration of the prediction model and genetic optimization algorithm, this framework can generate a large number of smooth hydrofoils and rapidly predict their hydrodynamic performance to achieve efficient optimization of hydrofoils. The optimized hydrofoil shapes obtained based on the above framework exhibit a higher lift-to-drag ratio than common hydrofoils. Furthermore, the optimized hydrofoils are applied to design tidal energy turbine blades. The simulation results demonstrate that the hydrodynamic performance of tidal turbines can be effectively improved through hydrofoil design optimization. The proposed framework enhances the design efficiency of the tidal turbine rotor and provides turbine hydrofoils with higher power coefficients.

A novel full-process test bench for deep-sea in-situ power generation systems

A novel full-process test bench was developed to replace lengthy and costly deep-water experiments. This platform can accurately simulate the dynamic characteristics of hydrokinetic turbines and can be used to evaluate their power-supply capabilities under various conditions. The hydrokinetic turbine power model was established by obtaining discrete performance data through experimentally validated computational fluid dynamics simulations and building surrogate models using the response surface methodology. This approach offers higher accuracy and broader applicability than empirical models. Moreover, a stepper motor platform based on a speed control scheme is proposed for the first time that can achieve high-precision transient simulation with a simplified control mechanism. This platform was employed to assess the power supply capacity of two hydrokinetic turbines under constant and typical deep-sea flow speeds. The ductless Archimedes screw hydrokinetic turbine was found to be more suitable for the deep water application than the high-solidity horizontal axis turbine due to its high self-start capacity and power coefficient. Furthermore, a case study was conducted on the design of a deep-sea in-situ power generation system at Luzon Undercurrent. Results suggest that a ductless Archimedes screw hydrokinetic turbine with a 1000 mm radius can comfortably cater to the energy demands of miniature AUVs.

Tidal turbine hydrofoil design and optimization based on deep learning

The optimal design of hydrofoils is critical to improve the hydrodynamic performance of the tidal turbine. However, the global optimization of hydrofoils is limited by the high dimensionality of the design space, which requires extensive computational fluid dynamics simulations. This paper proposes an interactive framework for hydrofoil design and optimization based on deep learning. Generative adversarial networks are used to parameterize the hydrofoil design, which automatically learns representations from existing hydrofoils and controls new hydrofoil generation using fewer variables to reduce optimization dimensions. Moreover, the surrogate model based on convolutional neural networks is constructed, which realizes the mapping of hydrofoil design and operating parameters to hydrodynamic performance parameters. The framework can generate a large number of smooth and realistic hydrofoils with three design variables and quickly predict the performance, enabling effective optimization design of hydrofoils. The results show that the optimized hydrofoil shapes have larger lift-to-drag ratios than those of the common hydrofoils. Furthermore, the optimized hydrofoil is applied to the design of 3D horizontal axis tidal turbine blades. The simulation results show that the framework is effective and stable, which can facilitate the design of tidal turbine rotors and provide hydrofoils with higher power coefficients.

Experimental and theoretical fluid dynamics of spherical Savonius turbines operated in pipe flows

The performance of Savonius turbines driven by flow in a pipe is experimentally investigated. The turbine is manufactured to have a spherical outline based on the pipe cross section at a small clearance. The torque and power of the turbine are obtained from the time derivative of the rotational speed measured using a high-speed camera and an equation of rotational motion. We find that the idling tip-speed ratio of the turbine exceeds 5, which is much greater than that of a turbine operating in an open free stream. This proves the dominance of pulsatile flow through the gap between two hemispherical blades in torque generation. Widely varying the gap (i.e., the overlap ratio OR of the Savonius turbine) reveals that a turbine with OR = 30 % has the highest power coefficient. The output efficiency exceeds 50 % for a tip-speed ratio of approximately 3. These experimental results are supported by fluid dynamics theory and computational fluid dynamics simulation, which clarify the driving mechanism of the turbine in a pipeline.

Trap-assisted monolayer ReSe2/Si heterojunction with high photoconductive gain and self-driven broadband photodetector.

The development of photodetectors is crucial in fields such as optical communication, image sensing, medical devices and military equipment, where high sensitivity is paramount. We fabricated an ambipolar photodiode using monolayer triclinic ReSe2, synthesized by chemical vapor deposition on p-type Si substrate. The photodetector has a broadband response range from 405 to 1100 nm. The device exhibits high sensitivity to NIR radiation with a high Iph/Idark (ON/OFF) ratio of 5.8 × 104, responsivity (R) of 465 A/W, and specific detectivity (D) of 4.8 × 1013 Jones at open circuit voltage (Voc), indicating photovoltaic behavior. Our ReSe2/Si heterojunction photodetector also exhibits low dark current of 1.4 × 10-9 A and high external quantum efficiency (EQE) of 54368.2% for 1060 nm at -3 V, demonstrating a photoconductive gain. The maximum responsivity (R = 465 A/W) can be achieved at -3 V reverse bias under 1060 nm. The device has a high ideality factor (4.8) and power coefficient (α = 0.5), indicating the presence of interface and sub-gap states that enhance device responsivity at lower illumination intensities by re-exciting trapped carriers into the conduction band. Our results offer important insights into the underlying photo-physics of the ReSe2/Si heterojunction and propose promising avenues for developing advanced broadband photodetectors of high performance.

Enhancing Efficiency and Reliability of Tidal Stream Energy Conversion through Swept-Blade Design

The current limited efficiency and reliability of tidal current turbines (TCTs) have posed significant challenges in effectively harnessing tidal stream energy. To address this issue, this paper undertakes both numerical and experimental studies to explore the advantages of swept blades over conventional straight blades in terms of energy capture efficiency and cavitation resistance. It is found that both the sweep length and sweep angle of the blade can influence the power generation efficiency of the TCT. For the particular swept blade investigated in this study, the highest power coefficient is achieved when the sweep length is 0.544 m and the sweep angle is 28.88°. The research also demonstrated that the swept-blade TCT shows a higher power generation efficiency than the straight-blade TCT across a broad range of rotor speeds. To be precise, with the swept blades, the power coefficient of the TCT can be improved by 5–17%, depending on the tip speed ratio. Additionally, swept blades exhibit a superior cavitation resistance. This is evidenced by their higher cavitation numbers across all tip speed ratios in comparison to conventional straight blades.

Numerical and experimental investigation of an Archimedes screw turbine for open channel water flow application

AbstractLow‐head turbines are becoming an agricultural imperative due to their high efficiency, low cost, ability to operate at low flow rates and minimal environmental impact. Therefore, the Archimedes screw turbine (AST) can play a leading role for producing electric power, especially in Pakistan's rural areas where most of the places have less than 1 m head. In this research work, performance evaluation of AST was carried out at different flow velocities in terms of power coefficient and torque generated. Design parameters such as blade width, blade pitches, and blade rotational angles are also used for performance evaluation. For this purpose, computational fluid dynamic (CFD) analyses of AST blades were conducted at different water flow velocities (e.g., 1, 1.5, 2, 2.5, 3, and 3.5 m/s). ANSYS FLUENT was used for AST blade simulations using three different design parameters such as blade width, blade pitch, and blade rotational angles. Additionally, CFD simulations have inherent errors and uncertainties that may lead to findings and deviations from their exact or real values. To prevent these uncertainties and errors, an experimental study was also conducted to provide validation for the CFD simulation results. The results revealed from CFD simulations for optimized design parameters were then compared with experimental data. From the results, it was examined that the numerical findings were in good agreement with the experiment data. The highest power coefficient and power output values were obtained under optimized design parameters such as inner and outer diameter, blade pitch, blade width, blade rotation angles and shaft length (e.g., 40 mm, 120 mm, 130 mm, 2 mm, 60°, and 850 mm respectively). The findings can be useful to implement the AST unit for those places where the available water head is ranging from 1 to 6.5 m and a flow rate of 0.2–6.5 m3/s, especially for rural areas of Pakistan.

Aerodynamic rotor design for a 25 MW offshore downwind turbine

Continuously increasing offshore wind turbine scales require rotor designs that maximize power and performance. Downwind rotors offer advantages in lower mass due to reduced potential for tower strike, and is especially true at large scales, e.g., for a 25 MW turbine. In this study, three 25 MW downwind rotors, each with different prescribed lift coefficient distributions were designed (chord, geometry, and twist) and compared to maximize power production at unprecedented scales and Reynolds numbers, including a new approach to optimize rotor tilt and coning based on aeroelastic effects. To achieve this objective the design process was focused on achieving high power coefficients, while maximizing swept area and minimizing blade mass. Maximizing swept area was achieved by prescribing pre-cone and shaft tilt angles to ensure the aeroelastic orientation when the blades point upwards was nearly vertical at nearly rated conditions. Maximizing the power coefficient was achieved by prescribing axial induction factor and lift coefficient distributions which were then used as inputs for an inverse rotor design tool. The resulting rotors were then simulated to compare performance and subsequently optimized for minimum rotor mass. To achieve these goals, a high Reynolds number design space was developed using computational predictions as well as new empirical correlations for flatback airfoil drag and maximum lift. Within this design space, three rotors of small, medium and large chords were considered for clean airfoil conditions (effects of premature transition were also considered but did not significantly modify the design space). The results indicated that the medium chord design provided the best performance, producing the highest power in Region 2 from simulations while resulting in the lowest rotor mass, both of which support minimum LCOE. The methodology developed herein can be used for the design of other extreme-scale (upwind and downwind) turbines.

Enhancing vertical axis wind turbine efficiency through leading edge tubercles: A multifaceted analysis

This research paper aims to investigate the impact of leading edge tubercles (LET) on the performance of hybrid vertical axis wind turbine (VAWT). The study involves both experimental and computational analysis of a novel hybrid VAWT configuration. The proposed VAWT design is characterized by a high power coefficient and self-starting capability. To provide a basis for comparison, an existing hybrid VAWT without tubercles and a conventional H-Rotor Darrieus design were also examined. The findings indicate that the proposed hybrid VAWT achieved the highest power coefficient (Cp) of 0.475 at a tip speed ratio (TSR) of 3. Furthermore, the proposed wind turbine demonstrated superior Cp values at both low TSRs (1 to 2.1) and high TSRs (4.1 to 5) compared to the existing hybrid VAWT and the H-Rotor Darrieus turbine. The positive static torque coefficient (Cts) values observed at all azimuths, with a maximum value of 0.319, highlight the self-starting capability of the proposed hybrid wind turbine. The enhanced power coefficient and the ability to harness wind energy even at low wind speeds make the proposed hybrid wind turbine suitable for a wide range of power projects, from small to large-scale. This approach offers a means to determine the optimal design configuration for a hybrid VAWT and facilitates a detailed analysis during the early design stages, along with its high-fidelity characteristics.

Low-speed, low induction multi-blade rotor for energy efficient small wind turbines

To promote the deployment of small wind turbines (SWTs), thorough understanding of design parameter implications is essential. In-depth research is required to comprehend the influence of design TSR on off-design wind speed performance of multi-blade SWTs. In-house built blade element momentum algorithm was employed, which considered Reynolds number dependence of aerodynamic coefficients and correlated well with experimental results. Peak power coefficients were produced for 0.9, 1.5, 2 and 3 m diameter S826 rotors with blade numbers from 2 to 12 and design TSR of 2–10. Remarkably, regardless of diameter, greatest CP,max values were achieved around design TSR of 4. For peak efficiency, smaller the diameter, narrower the blade number and design TSR range. High-speed rotors have wider TSR range for high power coefficient. Yet, it was shown that operating TSR of low-speed rotors deviates less from design TSR as wind speed varies. It was revealed that low-speed (with a threshold design TSR of 3), low-induction multi-blade rotors provide high CP,max, better efficiency at off-design, shorter starting time and lower wind speed than three-bladed high-speed rotor. A small boost in operational TSR was found to effectively mitigate loss in off-design performance. These are key features to maximize energy harvesting.

Experimental investigation and analysis of proposed hybrid vertical axis wind turbine design

In this research, an experimental and computational analysis of a novel hybrid vertical axis wind turbine (VAWT) arrangement has been performed. We suggest an innovative VAWT design that has a high power coefficient and self-starting capability. The inner side of the proposed hybrid system has been integrated with the H-rotor turbine with cambered blades, which demonstrates strong self-starting capabilities at various azimuths. Three NACA0018 airfoil blades are mounted on the outside of the proposed hybrid wind turbine, while three DU 06-W-200 airfoil blades are installed on the inside. Based on a similarity analysis, a scaled-down model was developed, and performance characteristics such as the output power, power coefficient ([Formula: see text]), dynamic torque coefficient ([Formula: see text]), and static torque coefficient ([Formula: see text]) were determined. An existing hybrid VAWT and a typical H-rotor Darrieus design were also examined for comparison. The highest [Formula: see text] for the proposed hybrid design was found to be 0.486 at a tip speed ratio (TSR) of 3, while the H-rotor Darrieus’ maximum value was 0.42 at a TSR of 2.62 and the existing hybrid VAWT’s value was 0.41 at a TSR of 2.5. Positive [Formula: see text] values at all azimuths demonstrate that the proposed hybrid wind turbine can start entirely on its own. In comparison to the existing H-rotor and hybrid VAWT, this novel hybrid system has shown enhanced performance parameters ([Formula: see text], [Formula: see text], [Formula: see text], output power) by around 11%–13% over a wide range of wind speeds.

Enhancing Savonius Vertical Axis Wind Turbine Performance: A Comprehensive Approach with Numerical Analysis and Experimental Investigations

Small-scale vertical-axis wind power generation technologies such as Savonius wind turbines are gaining popularity in suburban and urban settings. Although vertical-axis wind turbines (VAWTs) may not be as efficient as their horizontal-axis counterparts, they often present better opportunities for integration within building structures. The main issue stems from the suboptimal aerodynamic design of Savonius turbine blades, resulting in lower efficiency and power output. To address this, modern turbine designs focus on optimizing various geometric aspects of the turbine to improve aerodynamic performance, efficiency, and overall effectiveness. This study developed a unique optimization method, incorporating a new blade geometry with guide gap flow for Savonius wind turbine blade design. The aerodynamic characteristics of the Savonius wind turbine blade were extensively analyzed using 3D ANSYS CFX software. The optimization process emphasized the power coefficient as the objective function while considering blade profiles, overlap ratio, and blade number as crucial design parameters. This objective was accomplished using the design of experiments (DOE) method with the Minitab statistical software. The research findings revealed that the novel turbine design “OR0.109BS2BN2” outperformed the reference turbine with a 22.8% higher power coefficient. Furthermore, the results indicated a trade-off between the flow (swirling flow) through the gap guide flow and the impact blockage ratio, which resulted from the reduced channel width caused by the extended blade tip length.

CFD modeling of vertical-axis wind turbine wake interaction

Since wind turbines placed in wind farms need to minimize their footprint on the ground, the effects of the wake must be considered. Placement optimization, turbine spacing, and direction of rotation are known to affect the performance of vertical-axis wind turbines (VAWTs). However, rigorous numerical modeling methodologies that investigate the influence of these characteristics are lacking, especially in the case of large wind turbines. The goal of this study is to analyze turbine configurations that might enhance the power production of VAWT farms using two-dimensional CFD models based on the Star CCM+ package. The novelty of this work is to analyze wind farm configurations for very large turbines. This is important because large turbines are much more performant than small turbines and have a high power coefficient. Results show that CFD simulations adequately capture the performance of wind turbines in farms with multiple VAWTs. In general, if a second rotor is spaced more than 10 turbine diameters downstream of the first rotor, the effect of the wake is less significant. Furthermore, a specific farm configuration with five VAWTs is investigated and shows a 20% increase in power output compared with the same number of turbines operating in isolation.