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This paper investigated using spoilers to improve the aerodynamic characteristics of vertical-axis wind turbines. Taking the NACA0012 airfoil as the research object, the orthogonal experimental method design was employed to combine the parameters of the spoiler installation position. Then the wind energy utilization coefficient and the flow field structure of vertical-axis wind turbines were studied through numerical calculation, and the flow control mechanism of the spoiler and its effect on the aerodynamic performance of vertical-axis wind turbines were analyzed. The results show that the distance between the spoiler and the trailing edge of the blade is the main factor affecting the aerodynamic performance of vertical-axis wind turbines. By increasing the pressure difference between the suction and pressure surfaces of the blades, spoilers contribute to a higher aerodynamic performance of vertical-axis wind turbines. Additionally, the performance improvement effect on vertical-axis wind turbines is more significant at medium and low blade tip speed ratios. When the tip speed ratio is 1.8, the power coefficient of vertical axis wind turbines with spoilers is 25.3% higher than that of the original wind turbine. [ABSTRACT FROM AUTHOR]

Vertical axis small-scale wind turbines are gaining popularity because of their capacity to generate electricity from a renewable source by using wind from all directions. In this study the performance of a commercial Savonius vertical axis micro wind turbine with a rated maximum output of 2200 W have been analyzed through the modeling and simulation environment TRNSYS by varying the served building while installed into 5 different Italian cities. In particular, three typical different building typologies (a single-family dwelling, a small district consisting of 5 single-family dwellings, as well as an office) have been considered and the corresponding electric demands have been developed via an innovative stochastic approach. The climatic conditions have been taken into account by means of detailed weather data files. The building-integrated wind turbine's performance has been contrasted with a reference scenario that corresponds to the same building but uses the central electric grid exclusively. The comparison has been carried out from an energy, environmental, and economic perspective. The findings of simulations indicate that using the wind turbine can cut down the amount of electricity purchased from the central electric grid up to 37.51%, the global equivalent carbon dioxide emissions up to 37.74% and the operating costs up to 85.93%, with a minimum simple pay-back period of 1.09 years. [ABSTRACT FROM AUTHOR]

Wind turbines can freeze due to exposure to cold air. Ice formation on the rotor blades of a wind turbine reduces their performance. In the present work, the effects of ice formation on rotor blades of straight-blade vertical-axis wind turbines (SBVAWT) with a three-blade rotor and a NACA 0021 airfoil are numerically evaluated under two-dimensional transient settings by solving the continuity, momentum and turbulence equations become in ANSYS FLUENT. Grid and time step independence was investigated. For validation, the numerical model was compared with experimental data. An experimental ice model from the literature was then used to numerically simulate the iced rotor in twodimensional transition settings. The numerical simulation of the icy rotor was compared with an ice-free rotor. It was found that ice formation on the rotor blades changed the velocity and pressure fields around the rotor blades at angles of 180-360°, changing the streamlines and increasing the vortices. Furthermore, the maximum and minimum reductions in moment coefficient during blade icing occurred at angles of 225-315° and 45-135°, respectively. Due to ice formation on the rotor blades, the power coefficient of the rotor blades at angles 180-360° decreased drastically, and the power coefficient of the iced rotor was smaller than that of an ice-free rotor. It was concluded that ice formation on the blades of the SBVAWT reduced the average power coefficient of the blades and rotor power coefficient by 94.2% and 95%, respectively. [ABSTRACT FROM AUTHOR]

The self-starting performance of vertical-axis wind turbines (VAWTs) is crucial for their widespread utilization. Conventional evaluation methods using the static torque coefficient (CTS) or self-starting time have limitations. "The minimum 1st derivative of angular acceleration in the lift acceleration state" is proposed to serve as a suitable indicator for the completion of self-starting. Understanding the behavior of the self-starting process in VAWTs is crucial for optimizing power output. A comprehensive methodology is used that integrates experiments and computational fluid dynamics (CFD). Wind tunnel experiments are conducted to evaluate the self-starting and power output performance of the turbines. CFD is employed utilizing the Fluent 6DOF module to investigate the torque and flow field characteristics during the self-starting process. Additionally, the objectives of our study are to investigate the effect of static evaluation methods on the dynamic start-up process and to explore the effects of airfoil type, pitch angle, and inlet wind speed on the self-starting behavior of turbines. The results indicate that a high CTS ensures initial rotation, but the subsequent self-starting time remains independent of this factor. Increasing the pitch angle enhances the self-starting performance. At an inlet speed of 5 m/s, for the NACA2418 airfoil turbine, the self-starting times for pitch angles of 10° and 5° are reduced by 20% and 12%, respectively, compared to that for 0°. The NACA0018 airfoil turbines with pitch angles of 0° and 5° fail to complete selfstarting. The airfoil type also plays a crucial role, with the NACA2418 airfoil demonstrating superior self-starting performance and power performance. Furthermore, the minimum self-starting wind speed of the NACA0018 airfoil turbine was explored and determined be between 5.5 m/s and 6 m/s. The utilization of this novel self-starting evaluation method addresses the limitations of traditional approaches, providing a more universally applicable interpretation of the characteristics of turbine self-starting behavior. [ABSTRACT FROM AUTHOR]

The aim of this study is to evaluate the aerodynamic efficiency of a Savonius vertical-axis wind turbine. The approach used relies on resolving the Unsteady Reynolds Averaged Navier-Stokes equations (URANS), the turbulence being modeled by the k-ω SST model. The flow around the wind turbine is simulated using the arbitrary sliding interfaces technique. First, the study investigates the impact of blade shape on wind turbine efficiency by examining seven Savonius rotors constructed with distinct blade configurations. The results indicate that the highest aerodynamic performance is provided by the rotor with the elliptical blades, with a notable increase in the power coefficient of about 80% in comparison to the classic semi-circular profile. To further enhance the efficiency of the Savonius wind turbine, a twin-rotor configuration using the elliptical blades was studied. The results indicate a further enhancement in the power coefficient, reaching 110% compared to a single rotor with semicircular blades. [ABSTRACT FROM AUTHOR]

The deteriorating effects of greenhouse gases resulting from the use of fossil fuels have led to increased public attention to renewable energy sources, with wind energy being a particularly favored option. This prompted the development of various wind turbine types' efficiency. This study intends to explore the influence of key design parameters consisting of the number of blades, blade chord length, helical angle, and J-shaped blade on the performance and selfstarting ability of a Darrieus VAWT. Furthermore, implementing an efficient optimization model to obtain maximum power based on the numerical findings. To achieve this, two different numerical modeling approaches, namely Computational Fluid Dynamics (CFD) and Double Multi-Streamtube (DMST), have been applied. The results indicated that employing a higher blade number and chord length enhances the starting capability of the turbine. Moreover, increasing the helical angle to 60° reduces the generated torque fluctuations. Inspired by the design of the Savonius turbine, the implementation of a J-shaped airfoil boosted the Cp at low TSR. Finally, the Kriging optimization method has been employed to optimize the design parameters explored through CFD analysis. The outcomes showed that the optimum configuration of the examined Darrieus VAWT comprises a 3-bladed rotor with a blade chord length of 0.04 m and helical angle of 0° and a J-shaped blade length ratio of 0.68. This configuration yields an 10% increase in efficiency at the optimum TSR. [ABSTRACT FROM AUTHOR]

The market for small vertical axis wind turbines (VAWTs) continues to grow rapidly, filling up especially the low wind potential locations. Since the Saudi Government has announced to install 9 GW of wind power by 2032, this ambitious plan could be at least partially improved by the small wind turbines, taking into account the low annual mean wind speed on the most Kingdom of Saudi Arabia territory. However, the safety and durability of most commercially available VAWTs have not been adequately addressed with respect to the turbine over speed in high wind speed conditions. The presented research gives a methodology for calculating a cost-effective dynamic braking controller, based on a centrifugal mechanical activation spring-load mechanism with a pendulum. The analysis is focused on a small two-tier 3 kW Darrieus VAWT, where a mechanically activated friction brake is deployed as the turbine rotational speed approaches a red line. The proposed method makes a small turbine absolutely safe on any available wind speed and/or during accidental electric load switch off. The analysis was made for a typically high continental wind speed of 25 m/s. The paper presents the calculation model in VisSim software. Controller parameters were developed as the result of the research conducted on a functional turbine of the specific size in the model. The experiments covered two different cases: with a relatively low spring stiffness coefficient (400 N/m), showing the periodical oscillations of a controller pendulum on the cut-out speed and a high spring stiffness coefficient (4000 N/m), which the VAWT rotor can be surely braked at. The paper is intended to provide the mathematical basis for the scientific analysis, as well as providing practical implementation information to engineers building similar turbines, including Savonius, Darrieus, H-Darrieus, helix shape, V-type, and any other types of rotating rotors. The estimated capacity utilization factor (CUF) of any VAWTs, when using the proposed centrifugal mechanical controller, can be increased twice to 82% for on-land small VAWTs. [ABSTRACT FROM AUTHOR]

[Display omitted] • The hydrofoil-flap arrangement has a positive effect on the blade performance. • Experimental tests were carried out for two different hydrokinetic turbine rotors. • CFD analyses were conducted through 6-DoF user-defined functions. • The CP value increases about 20.53% when a hydrofoil-flap arrangement is used. • The rotor optimization is crucial for reducing the energy transformation costs. In this work, the efficiency of two horizontal-axis hydrokinetic turbines, whose blades were designed with and without multi-element hydrofoil cross-sections, has been numerical and experimentally investigated for tip speed ratio (λ) values ranging between 2.5 and 9.0 to compare the experimental rotor performance with numerical results. The Eppler 420 hydrofoil was used for the design of the blades applying the blade element momentum (BEM) theory. The variation of the power coefficient curve of the turbines was analyzed by using computational fluid dynamics (CFD) and experimental tests through ANSYs Fluent software with six-degrees of freedom (6-DoF) user-defined function (UDF) method and an open hydraulic channel, respectively. Numerically, for the turbine with a multi-element hydrofoil and without a multi-element (traditional) hydrofoil, maximum power coefficients ( C Pmax ) of 0.5050 and 0.419 (at a λ value equal to 7.129 and 6.739, respectively) were obtained. It is worth noting that a reasonable agreement between the numerical and the experimental results was achieved. In this regard, the blade with a multi-element hydrofoil has a positive influence on the hydrokinetic turbine performance; therefore, it can be used for power generation in river or marine systems. [ABSTRACT FROM AUTHOR]

Numerous studies have been conducted to investigate effect of blade geometry of vertical axis wind turbine performance. Most of the evaluations have focused on the airfoil series and airfoil geometry parameters such as thickness and camber of the airfoil. Few studies have examined the effect of other blade geometry parameters on the vertical axis wind turbine performance. In the present study, the effect of geometric change in leading-edge radius (LER) of a vertical axis wind turbine performance has been numerically studied. Hence, modified NACA 0021 airfoil profiles were created using the geometric method (CST). Then, the flow behavior around a Darrieus vertical axis wind turbine was simulated under the influence of the reduction and set-up coefficients of the leading-edge radius at a constant wind speed of 9 m/s and a tip speed ratio of 1.5 to 3.5 using the computational fluid dynamics. Additionally, the effects of the examined parameter (leading-edge radius) on fluid flow and aerodynamic performance coefficients, including the coefficients of power and torque, were investigated. The results indicated that the leading-edge radius affected the near wake flow of the turbine, and the optimization of leading-edge radius parameter controls the dynamic stall and reduces the formation of a vortex. Finally, the optimization of LER revealed that at 20% reduction in the LER the performance of the turbine at tip speed ratio of 1.5 was increased by more than 50%. This reinforces the self-starting capability of a Darrieus wind turbine. [ABSTRACT FROM AUTHOR]

Counter rotating Savonius wind turbine (CRSWT) is a vertical axis wind turbine (VAWT) which is appropriate for use in low-wind conditions. Experimenting to improve its performance is a difficult task because it is costly, time demanding, and complicated. CFD simulation with numerical prediction could be a good alternative. A novel change is introduced in this paper of two counter rotating Savonius wind turbines to enhance their efficiency. The suggested change includes curtain configurations as well as the insertion of fin to the blade. A CFD simulation was used to predict the effect of the proposed adjustments employing 'ANSYS FLUENT 16′. To avoid the opposing torque to each rotor rotation, the curtain arrangements were placed in front of both rotors. The fin was adopted to take advantage of the available area in the blade for directing wind flow. The performance of the rotor when fitted with various curtain arrangements, both with and without fin, was predicted and compared to that of the conventional CRSWT. The goal of these comparisons was to improve the geometrical data of the suggested curtain arrangements as well as to investigate the influence of fin addition on the blade. With the curtain arrangement having maximum curtain blade lengths (500 mm, 550 mm) and maximum angles (50°, 30°) and the addition of only one fin, the CRSWT's maximum power coefficient increased by nearly 48 percent. The simulation findings revealed that by selecting the right curtain arrangement and adding fins to the blade, the performance of the CRSWT could be greatly improved. [ABSTRACT FROM AUTHOR]

To further improve the lift-rising effect of the attached flap on an airfoil, based on the unique movement pattern of a fluke when a dolphin moves forward, this paper puts forward a novel attached split flap model with variable curvature. The lift-type vertical axis wind turbine's typical blade airfoil NACA 0018 is taken as the research object. First, the aerodynamic performance of the two-dimensional airfoil is simulated based on the SST k −ω turbulence model. The contrast between the simulation and the experimental results proves the correctness of the numerical simulation methods in this paper. Then, the effectiveness of split flap is verified, and the lift-rising principle is briefly analyzed. Finally, the parametric study is carried out based on the flap model with variable curvature proposed in this paper, and the lift-rising principle of the variable curvature split flap is analyzed in detail. The results indicate that, with the rise of the flap's curvature index, the airfoil's lift coefficient (Cl) integrated with the flap gradually increases accordingly and tends to a constant value. The bionic research in this paper can provide a comprehensive reference for the aerodynamic shape design of airfoil trailing edge flap and the further optimization of energy efficiency of rotating machinery or aviation. [ABSTRACT FROM AUTHOR]

Vertical axis wind turbines (VAWTs) work efficiently in low wind speed regions and varying wind directions like urban environments due to their omnidirectional capability. The current study examines experimentally the performance of the H-Darrieus VAWT having NACA 0018 airfoil by use of semi-cylindrical attachments at the trailing edge and hybridization using two bladed S-Savonius rotor with zero overlap conditions. The rotor's static torque and dynamic performances are investigated at a low wind speed of 4 m/s. The results show that the semi-cylindrical attachment increases the range of positive static torque. The static torque of Darrieus with attachment at 90° inside is more consistent, which enhances the starting capability of the Darrieus turbine with a static torque coefficient of 0.031, which is 29.7 % higher than a simple Darrieus turbine. The hybrid configuration shows maximum dynamic torque only at the 90° azimuthal position. The power coefficient of all configurations with attachments is lower than simple Darrieus due to drag created by attachments. The power coefficient value of 0.03 for hybrid configuration is the highest, with a wide range of tip speed ratio (TSR). • The performance of hybrid VAWT with semi-cylindrical attachment to the trailing edge at different angles was compared. • The maximum static torque coefficient of the Darrieus with attachment at 90° inside was 29.7 % higher than a simple one. • The semi-cylindrical attachments reduced the operating range. • The power coefficient of hybrid configuration was the highest with a wide range of TSR. [ABSTRACT FROM AUTHOR]

Clean energy sources like wind energy have been receiving much attention, and great emphasis has been given to the design and optimization of horizontal axis wind turbines, but just as important are the vertical axis wind turbines that can be used for generating energy for small businesses, houses, and buildings. This article sought to study the optimal geometrical parameters of a H-Darrieus vertical axis wind turbine using surrogate-based optimization with three different types of surrogate models and compared them. Airfoil chord and thickness were chosen as the design variables and respective ranges set at 0.32-0.6 m and 0.04-0.16 m. All evaluations are carried out for a tip-speed ratio of 1.5. Three different surrogate models were used and compared, namely a quadratic polynomial response surface, an artificial neural network based on radial basis functions called Extreme Learning Machine and a Kriging interpolator. Surrogates were constructed based on an initial sample data distributed according to a full factorial design. A test set was designed to evaluate the accuracy of the surrogates. Both training and testing data sets were generated using 2D CFD modeling to reduce computational cost. From the test set, Extreme Learning Machine surrogate showed the smallest RMSE of 11.24%, followed by Kriging, at 17.64%, and Response Surface of 22.17%. For the optimal designs the same pattern ensued, with optimal power coefficient overestimated by 8.7% for the response surface surrogate, followed by 3.12% and 2.17% for the Kriging interpolator and the Extreme Learning Machine, respectively. Power coefficient curves comparing the three optimal geometries from each surrogate were calculated and plotted. Optimal turbine obtained from Kriging surrogate optimization process resulted in a 7.92% increase in the Cp, whilst Extreme Learning Machine and Response Surface resulted in a 7.86% and 4.29% increase, respectively, all when compared to baseline CFD model. Concluding guidelines are that the quadratic polynomial response surface may not be the best alternative when dealing with complex non-linear relationships as typically present in VAWT simulations. Superior techniques such as Extreme Learning Machine and Kriging could be more suitable for this application. [ABSTRACT FROM AUTHOR]

Wind energy conversion is contributing significantly to the new clean energy transition but, up to now, such contribution is mainly driven by large multi-MW windfarms. On the other hand, the recent needs in terms of distributed energy production are revealing a new interest in small-scale wind energy conversion technologies for residential and urban applications. In this context, vertical axis wind turbines (VAWT) are often the most valid choice from the point of view of building integrating possibilities, but it is well known that they suffer a considerable gap in performance when compared to horizontal axis technologies. Based on these premises, in the present work some innovative solutions for improving the performance of a Darrieus vertical axis wind turbine are investigated through numerical and engineering approaches. The investigated interventions include rotor hybridization by the use of an inner Savonius section for improving the machine's start-up and the possible application of dimples for improving the NACA 0021 airfoil performances on the outer rotor section. Results demonstrate the effectiveness of the interventions in obtaining a rotor with stable performances in a very wide range of wind regimes. • Vertical axis wind turbines (VAWT) are the most valid choice for building integration • It can be important to fill the performance gap compared to horizontal axis machines • The improvement of the Darrieus VAWT is studied by the use of a hybrid rotor • The maximum performance can be also achieved with the possible application of dimples [ABSTRACT FROM AUTHOR]

This article presents the urban wind potential that exists in the provinces of the Dominican Republic through free access data provided by numerical weather prediction and geographical information systems. Then, a hybrid Strengths, Weaknesses, Opportunities, and Threats (SWOT) – Analytic Hierarchy Process (AHP) analysis was conducted to qualitatively determine the factors that influence urban wind energy, and the weighting of these through expert judgments, quantifying the prioritized factors. The results show that the average consolidated urban wind speed is 3.66 m/s at 10 m height, and the predominant direction is 86°. Adopting the parameters of the Weibull distribution, an Annual Energy Production (AEP) of 1,145 kWh/y is estimated for one small wind turbine. Assuming that ten 2-blade Darrieus H-type vertical axis wind turbines are installed in each province, the global AEP is 423,936 kWh/y. Applying the hybrid analysis with the combination of the factors, the results indicate that the strengths and opportunities represent 0.693 and the weaknesses and threats are 0.307. The most important SWOT factors of each category were i) low emission of greenhouse gasses (internal), ii) low energy sale price of surplus energy to the grid (internal), iii) use of public policies (external) and iv) bureaucracy and slow processes in public companies related to permits (external). [Display omitted] • Framework to urban wind energy assessment integrating SWOT – AHP analysis • Urban wind energy potential through numerical weather prediction • 69.3 % of factors that could influencing urban wind energy are deems as positive. • Bureaucracy and low energy sales price are the most adverse factors. • Quantifying the factors that influence urban wind energy through AHP analysis [ABSTRACT FROM AUTHOR]

This paper presents an investigation of an axial generator for a small vertical-axis wind turbine. The performance of the axial generator design is tested by knowing the output voltage produced by varying the rotation. The generator is designed to generate three phases of electric power. And then through the wind turbine controller, three phases of alternating current are converted into direct current/DC. The Axial generator uses neodymium permanent magnets with many winding poles of 12 pieces. The coil uses 0.5 mm diameter copper enamel wire with a total of 400 turns each. A voltage of 30 Volt DC is obtained for the rotation of the axial generator at 300 rpm. For application, the generator can be used for a small vertical-axis wind turbine for stand-alone street lighting, which needs only 12 Volt of DC. [ABSTRACT FROM AUTHOR]

The high power coefficient of the Darrius vertical axis wind turbine lift regime has prompted researchers to concentrate their efforts on this regime, despite the fact that these turbines suffer from major problems in the drag-lift regime. In the present study, in addition to exploring the performance of the Darrius type wind turbine at blade tip speeds Ratio above 1, the effect of design factors on its performance at TSRs below 1 is also investigated. The results were extracted from numerical analysis recruiting Fluent software and the k-w SST turbulence model. The effect of blade type, thickness, and chord length on turbine performance has been investigated. The blade angle of attack (AOA) at TSR less than one was calculated using a new equation, and the results were evaluated. The numerical study of the Darrius wind turbine showed that increasing the chord length for symmetric and asymmetric airfoils from 0.1 to 0.2 m enhances the turbine performance in drag-lift regime, whereas decreasing chord length improves turbine performance at higher TSRs. The blade with a curvature of 4 % and a chord length of 0.1 m has the best performance at TSR 2.25. Increasing the thickness from 18 to 22 % of chord length exerts a negative influence on the turbine's performance in both regimes, and at lower TSRs, NACA0018 airfoil with a chord length of 0.2 m was of the optimum performance in the drag-lift regime. [ABSTRACT FROM AUTHOR]

Wind energy is an alternative future energy to fossil fuels since it is abundant and green energy. As a result, high performance unique design is proposed that has a diffuser augmented wind turbine including intake funnel with guide vanes, natural fan, straight flow section, exit splitter with air openings and end flange. This proposed design is called as Integrated omni-directional Intake funnel, Natural fan, Straight diffuser, Splitter and Flange (I²NS²F) Design. To construct this I²NS²F configuration, four distinct wind turbines were developed: a) bare wind turbine, b) wind turbine diffuser design with single rotor turbine, c) bend diffuser, intake funnel, natural fan, splitter and flange and d) I²NS²F design. The proposed designs are numerically studied using MATLAB Simulink and Ansys Fluent. These designs are optimized by Random Search Optimization with Supervisory Control and Data Acquisition technique to evaluate the wind velocity and the performance is comparatively estimated. From this analysis, I²NS²F design achieves 53m/s of wind velocity at turbine region for 5.5m/s inlet wind and it could be considered as highest wind velocity than other three designs. It is evidently proved and concluded that proposed I2NS2F design augments natural wind, resulting in greater green power generation. [ABSTRACT FROM AUTHOR]

Vertical Axis Wind Turbine (VAWT) is a wind power plant with many advantages, especially as a renewable energy source. Through the pocket of Science-Technology-Engineering-Art-Mathematics (STEAM) learning, this study designs a VAWT and explores the potential of this tool for learning. This study used a mixed-method embedded design with an experimental and interview type. The research results show that the influence of the number of blades and wind speed on voltage, current strength, and power is directly proportional. Therefore, VAWT can also be used as one of the projects for STEAM-based learning. [ABSTRACT FROM AUTHOR]

In this study, the overall aerodynamic performance of the airfoils with variable amplitude geometric structure for lift-type vertical axis wind turbine has been analyzed and optimized using Fuzzy Analytic Hierarchy Process (AHP)-Fuzzy COmbinative Distance-based Assessment (CODAS) based on Taguchi Method. In the design of the experiment, leading edge (LE) tubercle airfoil models, Reynolds number, and angle of attack are utilized as the control factors. Drag, lift, and lift to drag ratio performances by comparing the airfoils according to the baseline model are calculated and the combination of these performances is considered as the overall aerodynamic performance response. The experiments are carried out according to the orthogonal matrix L18. Since the importance of each response is different on lift-type vertical axis wind turbines, the importance weights of these responses were obtained by Fuzzy AHP according to the evaluation of the decision maker. Multiple responses are converted into a single response (the overall aerodynamic performance) via Fuzzy CODAS which enables to model uncertainty in order to overcome the physical effects that may arise in experiments. Thereby, a multi objective Taguchi methodology was applied for the overall aerodynamic performance with a novel Fuzzy logic based multi criteria decision analysis approach. As a result, Model-4, having tubercle design parameters of amplitude of 0.025c and 0.0125c and wavelength of 0.5c and 0.125c, was found to have the best performance with the novel Taguchi approach, which saves time and cost. In addition, it has been determined that the airfoils, Reynolds number and angle of attack are significant and what level of contribution to the overall aerodynamic performance. At this point, the most important control factor has emerged as the angle of attack. [Display omitted] • Overall performance of airfoils was determined by using Taguchi, Fuzzy AHP-CODAS. • The hybrid fuzzy decision making based Taguchi approach was proposed for the first time. • The importance weights of the responses were obtained by Fuzzy AHP. • The most successful wing model for overall aerodynamic performance was Model 4. • Most influential factor on overall performance was determined as angle of attack. [ABSTRACT FROM AUTHOR]

This paper aims to enhance the performance of H-Darrieus Vertical Axis Wind Turbine (VAWT) via introducing upstream deflectors. The impact of this addition has been investigated and discussed through different deflector configurations. The turbine performance before and after adding different wind rotor barriers was compared. A two dimensional, incompressible, transient, and turbulent flow model was built up in order to simulate the air flow around the turbine blades. Model verification and validation were performed through comparing the model solutions using different mesh sizes, time steps, turbulent models, and discretization schemes. Computational Fluid Dynamics (CFD) models were validated to provide novel insights on the effect of the deflectors on the aerodynamic characteristics of a VAWT blades. Results showed that the presence of a single deflector increases the highest value of the moment coefficient of the bare configuration by 24%, either increases the negative torque values, while two defectors increase the maximum value by 22% and the overall average value of the moment coefficient over the optimal range for the tip speed ratio. [ABSTRACT FROM AUTHOR]

Savonius turbine is a vertical axis wind turbine (VAWT) which is suitable to operate at low wind velocities. The experimental investigation to improve its performance is a big challenge as; it is expensive, complicating and time consuming. Numerical prediction using CFD simulation could be a valuable alternative. This paper introduces a new modification of Savonius wind rotors to improve its performance. The proposed modification consists of a curtain arrangement together with fin addition on blade. The effect of the proposed modification was predicted using a CFD simulation employing 'ANSYS FLUENT 16′. The curtain arrangement was located in front of the rotor to avoid the opposing torque to the rotor rotation. The fins were added to exploit the space in the blade for guiding the wind flow. The performance of the rotor with different curtain arrangements and variable number of fins was predicted and assessed against that of the conventional rotor. This comparison aimed to optimize the geometrical data of the proposed curtain arrangement with the number of added fins. The maximum power coefficient of the Savonius wind rotor was found to be increased to about 42 % with the optimum curtain arrangement (lengths of the curtain blades 1000 and 1150 mm and the angles of the curtain blades 30 and 50) together with adding only one fin. The simulation results showed that the performance of Savonius wind rotors could be significantly enhanced with a proper selection of curtain arrangement and number of fins to be added on the blade. [ABSTRACT FROM AUTHOR]

This paper illustrates the investigation of higher-scale interconnected wind turbine to realize its analytical design and simulation performance in terms of reduced order model. The present research is aimed to visualize the efficacy of the propounded harris hawks optimization (HHO) approach for different reduced order transfer functions with reference to model order reduction studies. Compared to the higher-scale model, the applied methodology aims to obtain better results in terms of steadiness and computational effort. Moreover, to realize a higher-dimensional power system, the implementation of the HHO may proffer more effectiveness and robustness as opposed to the state-of-the-art optimization techniques. The applied methodology aims to obtain better results in terms of stability and computational effort. Furthermore, to realize a higher dimensional system, implementation of the HHO may offer more effectiveness and robustness as opposed to the state-of-the-art optimization techniques. • Novel HHO integrated MOR for interconnected wind turbines have been devised. • Optimization approach using HHO has been realized. • Comparative analysis in terms of various control domains has been structured. [ABSTRACT FROM AUTHOR]

This is the second part of a two-part paper focusing on the flow instabilities of low-specific speed pump turbines. In this part, results of the flow control application with fluid injection in the vaneless space for suppressing the flow instabilities of a model pump turbine in turbine mode operation at HSLU (Lucerne University of Applied Sciences) Switzerland are presented. Using the experimental data and CFD results, the onset and development of flow instabilities are explored in the first part of this paper. Based on these analyses, a flow control technology using injection of fluid in the vaneless space of the model pump turbine is implemented in order to suppress the flow instabilities and, thereby, to extend the operating range. Through use of an external energy source, air and water injection are applied with discrete nozzles that are circumferentially distributed in the vaneless space. The S-shaped pump turbine characteristics in turbine operating mode are modified so that the slope at speed no load conditions is no more positive meaning an improvement in the stability behavior. To the best of our knowledge, this is the first successful application of flow control with fluid injection in the vaneless space of pump turbines. Fluid injection is applied at two different guide vane openings. The analysis of the unsteady pressure data indicates that fluid injection in the vaneless space suppresses the flow instability such as rotating stall. Moreover, the water injection turns out to be more effective than the air injection for modifying the slope of the pump turbine characteristics. [ABSTRACT FROM AUTHOR]

Wake generated by wind turbine can greatly influence the performance of downstream turbine. To better understand the wake self-similarity characteristics of vertical axis wind turbine (VAWT), the shear stress transport (SST) turbulence model with the addition of the γ-Reθ transition model is performed to model a twoblade VAWT at different operating conditions. The simulated blade surface pressure and torque are compared with existing experimental results for validation. Results show that, the simulated results after considering the transition model are more consistent with the experimental results. Analysis of the flow field shows that the average streamwise velocity of the wake in the horizontal plane under different tip speed ratios is asymmetry, but symmetric in the vertical plane. Further analysis indicates that, at different downstream positions, the nondimensional streamwise velocity deficit in the vertical plane remains self-similarity and basically coincides with the Gaussian distribution curve exclude the wake edges. In addition, the larger the tip speed ratio, the easier streamwise velocity deficit reach self-similarity state at downstream of the VAWT. The results of this study will be helpful to establish the wake model of the VAWT. [ABSTRACT FROM AUTHOR]

The present article analyses the mechanical behaviour of a natural composite VAWT (Vertical Axis Wind Turbine) blade constituted of fique and epoxy. The analysis was made using FEM (Finite Element Method) applying the wind forces. The increasing usage of renewable energies and environmental care in the last decades have required new materials to reduce the solid waste produced by the typical composites made of fiberglass and epoxy. Using biodegradable materials provides a solution to reduce the environmental impact. For instance, fique composite is studied and analysed as an option to manufacture VAWT blades. The aim of this research is to provide a computational model to analyse the strain and stress distribution, confirming a design of a VAWT blade using a fique and epoxy composite, subdued to wind forces. A computational model was generated on ANSYS software, including the anisotropic properties of the material. The numerical model recreates a VAWT blade geometry, and the number of plies was variated to obtain an acceptable stress-mass ratio. The stress distribution was obtained over the VAWT blade geometry using fique-epoxy composite. Principal stresses were contrasted to determine the critical region. The usage of a stiffener was implemented to reduce the stress peaks. [ABSTRACT FROM AUTHOR]

This work presents the results of the development of a vertical axis wind turbine composed of variable geometry, plane blades, applied in operations with low wind speeds. The new concept of vertical axis wind turbine with variable opening blades is presented as an innovative prototype where mechanical details are important for the natural control of the openings of the blades. Theoretical, numerical and experimental analyzes are performed in the turbine called DEC® with the aim of determining the aerodynamic characteristics. An analysis of the behavior of the DEC® turbine consists of a numerical study carried out to calculate or drag coefficient, considering a range of opening positions of the opening at each moment to determine the power coefficient. A second numerical approach is to analyze the moment caused by the interaction between all the turbine blades, in which the effects of energy dissipation caused by the flow mats are considered. Then, the theoretical, numerical results are validated by tests performed using a model in the open wind tunnel, where the prototype is subjected to different wind speeds while maintaining rotation control. Suggestions are made to improve the mechanical and aerodynamic design of the innovative prototype. Finally, the DEC® turbine is expected to serve as an inspiration for creating other mechanical forms of passive or active control to improve variable aerodynamics applied in low-speed conditions. [ABSTRACT FROM AUTHOR]

Vertical axis wind turbines (VAWTS) can be a suitable choice for usage in urban areas. Wind conditions and structural parameters are critical to power production. In this study, some variations of a darrieus vawt was attempted via wind tunnel testing. A modified naca4412 blade profile was selected for this investigation. The influence of aspect ratios, angle of attack, chord length, etc. were investigated experimentally. After taken more than 800 data artificial neural network (ANN) was applied to estimate the other range of scales using different algorithms that are utilized the aforementioned experimental parameters. This study focuses on the design criteria and application of VAWTS inbuilt real environments without testing. The results have been promising and will provide ease of design for similar designs. Moreover, this work will contribute to environmental cleanup and a more livable world by increasing renewable energy resources. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Harbin Institute of Technology. Social Sciences Edition / Haerbin Gongye Daxue Xuebao. Shehui Kexue Ban is the property of Harbin Institute of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Wind energy is one of the abundantly available renewable energy resources. Savonius vertical axis wind turbine is better suited for small scale power generation applications with many advantages. The turbine operates independent of wind direction with good starting torque and less noise. But, the power coefficient of the Savonius turbine is less than all other wind turbines. The shape of the turbine blades plays an important role in the performance of the turbine. In this present two-dimensional numerical study, an attempt has been made to improve the turbine performance by considering three types of blade shapes. The complete design details of the proposed new blade shapes are presented. The simulations are carried out using ANSYS Fluent 15.0 with SST K-ω turbulence model. The power coefficient of the modified blade is found to have increased by 20% compared to conventional blade shape. The effect of tip-speed-ratio on power coefficient has also been studied and reported. [ABSTRACT FROM AUTHOR]

Presently the two primary causes of the energy issue are the world's fast growing population and rapid improvement in people's living standard. As a result, there is an energy crisis that affects everyone in the world, and the cost of energy is increasing. It is generally acknowledged that the energy as we now use, will not be adequate to meet the needs of all people on the planet in future, hence cleaner and more plentiful alternative energy sources are required which may be in the form of hybrid energy also. Renewable energy sources will certainly become more prominent. Modern civilizations needs cheap, plentiful energy to survive, therefore, it is crucial for human civilization to create a sustainable, affordable, and environmentally benign alternative sources of energy. The global energy dilemma may have an efficient solution in the form of wind power. It is a source of clean and green energy that is completely safe, affordable, and an environmentally friendly. In current state of affairs, the air could seems like insignificant to any or all. However we tend to all grasp that, the planet has shaped up with associate uneven surface, which suggest that the sunrays could strike these surface with variable intensities at numerous spot on its uneven surface. This creates associated degree of unequal degree of heating of the earth surface, that which causes variation in part of atmospheric pressure thereon. Then it leads to wind. The Kinetic energy of these air molecules is nothing but wind energy. A mechanical mechanism known as a wind turbine which transforms, kinetic energy which is there in the air around it into the required form of mechanical energy. Here in this research we focused on the repellent qualities of permanently magnetized objects with similar poles. These innate qualities of magnetic propulsion are used here as an energy sources. Due to the inclusion of this components like magnetic repulsion, our VAWT system will operate more effectively even at lower wind speeds circumstance also. This magnets will produce a repulsive force that will add various sorts of kinetic energies to the wind turbines as they convert wind energy's kinetic energy of into the necessary mechanical power when it's employed as an extra source of energy in a VAWT. [ABSTRACT FROM AUTHOR]

This study presents experimental and numerical investigation for the effect of number of blade (solidity) on the power and thrust coefficients of a small-scale horizontal-axis wind turbine HAWT. An experimental set- up was installed on wind turbine rotors with different number of blades, i.e. three, five and six, and at different tip speed ratios, in the closed-circuit open-test section wind tunnel. The obtained results from CFD simulations were performed to compare numerical data with experimental measurements. In addition, there is a lack of information presented for the effect of rotor blade number on the flow field for HAWT like vertical axis wind turbine VAWT. Therefore, the current study extends to study the effect of solidity on the flow field using numerical calculation. The numerical simulation was performed using a steady-RANS method. The SST k- ω turbulence model was used to represent turbulence characteristics. It is found that decreasing the number of blades (which makes the turbine less sensitive to the change in tip speed ratio) the wind turbine with 3 blade configuration has the maximum power coefficient in respect to 5 and 6 blade turbines, higher by around 2 and 4 percent respectively. [ABSTRACT FROM AUTHOR]

A novel positive displacement, high pressure, vertical axis wind pump (HP-VAWP) was evaluated for the application of stand-alone high-pressure reverse-osmosis desalination and drip irrigation systems. The direct interface between a vertical axis wind turbine (VAWT) and a positive displacement pump that delivers a constant liquid volume per revolution has never been studied before. Understanding the interaction between turbine and pump efficiencies, where delivery pressure is determined by back-pressure alone, is critical for efficient design. Wind tunnel experiments were conducted on a small-scale two-bladed turbine (0.4 m cross-sectional area) that operated on a dynamic stall principle. At these small laboratory scales, the turbine and pump peak efficiencies were relatively low (15% and 28%, respectively); nevertheless, the system produced nearly constant pressures in excess of 1.5bar for a broad operational range. Moreover, the system exhibited a basic self-priming capability, and the turbine could easily be braked by overloading the pump. A conservative field-scale analysis of an HP-VAWP system indicated that a medium-size turbine (12.5 m2 cross-sectional area) could attain a peak efficiency of 12.9%. Realistic efficiencies greater than 20% are attainable, significantly exceeding the 4%-8% typical peak efficiency of the widely used American multibladed wind pumps. Indeed, our research indicates that an HP-VAWP system is viable and requires further development. The benefits of zero carbon emissions during operation, high relative efficiency, and easy manufacturing and maintenance render the HP-VAWP ideal for stand-alone or off-grid environments. [ABSTRACT FROM AUTHOR]

The aim of this work is to carry out an aerodynamic analysis to assess the power and identify the characteristics of the horizontal axis Magnus type wind turbine with spiral fins. A parametric study is achieved to analyze the effects of the different influence parameters such as the turbine tip speed ratio, the cylinder spinning ratio, the blade aspect ratio and the cylinder hub-tip ratio. The analysis approach adopted in this study is the Blade Element Momentum BEM using the experimental lift coefficient data for the configuration of spinning cylinders with spiral fins. In this analysis, losses are not taken in consideration. Both axial and angular interference coefficients are evaluated for this type of wind turbine. The former is assessed by solving a quadratic equation and the latter is calculated from a classic formulation including the term of spinning. An iterative process is followed to achieve this task. Concerning the obtained results, the aerodynamic characteristics of the Magnus wind turbine, analyzed in this study, provide some elucidation to lead a successful preliminary design of this novel type of machine. [ABSTRACT FROM AUTHOR]

Improving the aerodynamic performance of the transonic fan in a turbofan engine can be beneficial for both the fuel consumption and maneuverability of an airplane. Deep insight into the supersonic aerodynamics is needed for the simultaneous improvement of all operating parameters of a transonic rotor, including the pressure ratio, efficiency, and surge margin. A design method was developed for an axial transonic rotor by using a combination of radial equilibrium theory, the free vortex method, and a distributed span-wise diffusion factor. The loading distribution obtained by this method was the highest in the hub section and gradually decreased in the tip section. To evaluate the method, a transonic rotor was designed using the geometric parameters and operating conditions of NASA rotor 67. A code was developed to determine a geometry for the new rotor and to modify it. The code was coupled with a RANS flow solver for 3D modification of the new designed rotor. Only standard multi- and double-circular arc airfoils were applied in different radial sections of the new rotor with no blade profile optimization. The results of the RANS equations solution for the new designed rotor showed 1.5% higher efficiency, 3% higher pressure ratio, and more than 1.5 times larger operating range in comparison to NASA rotor 67. The new designed method seems to be an efficient approach that not only improved the efficiency and pressure ratio but also increased the operating range of an axial transonic rotor. [ABSTRACT FROM AUTHOR]

The motion state of a floating platform and turbine in a flow field is analyzed by using seakeeping theory. Without considering the floating platform, the energy capture efficiency of the turbine in the flow field is compared by obtaining the hydrodynamic performance of the turbine impeller flow field at different velocities and tip speed ratios. Through processing and analyzing the complex sea conditions' data, the selected working sea conditions and extreme sea conditions for calculation are combined with the environmental load data to simulate and measure the energy capture efficiency variation of turbines subjected to single-degreeof- freedom fluctuations (pitch or surge). It has important reference value to subsequent research of the turbine working in complex sea conditions, multiflow- field coupling calculation, and structural improvement design. [ABSTRACT FROM AUTHOR]

Wind energy is one of the most promising renewable energy resources in terms of cost, environmentally friendly, and sustainability. Accordingly, exploiting its full potential has extensively attracted researchers to cope with the depletion of traditional energy resources. In this paper, enhancements in the design of a vertical axis wind turbine have been suggested, which entail employing self-oriented flat blades for improving the turbine's efficiency. Basically, the proposed design depends on utilizing a mechanical mechanism that is effectively capable of providing the turbine blades with the ability to reorient themselves. This self-oriented motion assures a continually perpendicular orientation between the affecting wind direction and the blade surface. Besides, it has been proposed that the turbine should be enclosed in a self-oriented cylindrical rotary cage that has an inlet for airflow. This cage rotates by self-motion without using motors for adjusting its inlet towards the affecting wind direction. To assess the proposed design validity, a vertical wind turbine prototype with the proposed attachments has been built and efficiency improvements have been reported. Moreover, the results of the experimental and theoretical natural frequencies ensured that the proposed turbine design can safely work for considerably high angular speeds with no risk of resonance scenarios. [ABSTRACT FROM AUTHOR]

All human actions necessitate energy resources. Currently, a major part of our energy requirements is supplied by fossil fuels, which are fated with uncertainties concerning their availability in the forthcoming decades. However, the combustion o f fuels results in adverse environmental aftermaths. Energy of wind falls into one of the clean and renewable energy resources. Wind power is generated using horizontal and vertical axis wind turbines (HAWTs & VAWTs). VAWTs operate appropriately under low wind velocity conditions to generate power in small scales. On the other hand, numerous VAWT designs have been presented to enhance their performance in such circumsances. This study is aimed at developing cost-effective aerodynamic calculations models for both Gorlov and Darrieus straight-bladed VAWT types. Thus, DMST (double multiple stream tube) models, which act on the basis of BEM (blade element momentum) theory, have been designed for Gorlov and Darrieus VAWTs. By comparison of the results obtained with those available in the literature, the models developed are validated. Additionally, the performance of the Darrieus-type straight-bladed VAWTs was compared to that of the Gorlov VAWTs. According to the findings, although the peak power coefficient (CP) decreased slightly for Gorlov VAWTs in comparison with the Darrieus straight-bladed type, the Gorlov rotor showed improved performance in terms of fluctuation and effectiveness based on the torque coefficient curve of helical blades. [ABSTRACT FROM AUTHOR]

Onsite utilization of wind energy in the urban environment is an effective solution to environmental protection and energy security. The typically micro wind turbines, including Savonius vertical axis wind turbine, H-type vertical axis wind turbine and micro horizontal axis wind turbine are more suitable for distributed generation, relative to centralized generation of large scale wind turbines. However, the wind in the urban environment characterized by low wind speed, high levels of turbulence and strongly unsteady direction and speed, directly affecting the aerodynamic characteristics of wind turbine. In the present work, wind tunnel tests have been conducted to investigate the low Reynolds number effect on aerodynamic characteristics for these three typical micro wind turbines, and the aerodynamic differences among them have been compared qualitatively and quantitatively. The experimental results show that micro horizontal axis wind turbine and H-type vertical axis wind turbine, belonging to lift-type wind turbine, have relatively higher startup wind speed and lower power coefficient due to deteriorative aerodynamic performance of airfoil at low wind speed. However, Savonius vertical axis wind turbine, as a drag-type wind turbine, exhibits excellent aerodynamic performance at low Reynolds number. The Savonius wind turbine has apparent output power at 5m/s, and the peak power coefficient exceeding 0.2 at 9m/s being superior to that of two other lift-type wind turbines at the same wind speed. In addition, in consideration of natural advantage of vertical axis wind turbine, Savonius wind turbine is the best option for applying at low Reynolds number urban environment. [ABSTRACT FROM AUTHOR]

Onsite utilization of wind energy in the urban environment is an effective solution to environmental protection and energy security. The typically micro wind turbines, including Savonius vertical axis wind turbine, H-type vertical axis wind turbine and micro horizontal axis wind turbine are more suitable for distributed generation, relative to centralized generation of large scale wind turbines. However, the wind in the urban environment characterized by low wind speed, high levels of turbulence and strongly unsteady direction and speed, directly affecting the aerodynamic characteristics of wind turbine. In the present work, wind tunnel tests have been conducted to investigate the low Reynolds number effect on aerodynamic characteristics for these three typical micro wind turbines, and the aerodynamic differences among them have been compared qualitatively and quantitatively. The experimental results show that micro horizontal axis wind turbine and H-type vertical axis wind turbine, belonging to lift-type wind turbine, have relatively higher startup wind speed and lower power coefficient due to deteriorative aerodynamic performance of airfoil at low wind speed. However, Savonius vertical axis wind turbine, as a drag-type wind turbine, exhibits excellent aerodynamic performance at low Reynolds number. The Savonius wind turbine has apparent output power at 5m/s, and the peak power coefficient exceeding 0.2 at 9m/s being superior to that of two other lift-type wind turbines at the same wind speed. In addition, in consideration of natural advantage of vertical axis wind turbine, Savonius wind turbine is the best option for applying at low Reynolds number urban environment. [ABSTRACT FROM AUTHOR]

A numerical study was carried out to investigate the effects of a Gurney flap (GF) on the aerodynamics performance of the NACA 00 aerofoil and an associated three-blade rotor of a H-type Darrieus wind turbine. The flow fields around a single aerofoil and the vertical axis wind turbine (VAWT) rotor are studied using unsteady Reynolds-averaged Navier-Stokes equations (URANS). The height of GF ranges from 1% to 5% of the aerofoil chord length. The results show that the GF can increase the lift and lift-to-drag ratio of the aerofoil as associated with the generation of additional vortices near the aerofoil trailing edge. As a result, adding a GF can significantly improve the power coefficient of the VAWT at low tip speed ratio (TSR), where it typically gives low power production. The causing mechanism is discussed in detail, pointing to flow separation and dynamic stall delay. [ABSTRACT FROM AUTHOR]

Pump performance characteristics of pump turbines in transient processes are significantly different from those in steady processes. In the present paper, transient processes of a flow rate that increased and decreased in the pump mode of a model pump turbine were simulated through unsteady simulations using the shear stress transport (SST) k-ω turbulence model. The numerical results reveal that there is a larger hysteresis loop in the performance characteristics of the increasing and decreasing directions of the flow rate compared with those of steady results. Detailed discussions are carried out to determine the generation mechanism of obvious hysteresis characteristics using the methods of entropy production and continuous wavelet analysis. Analyses show that the states of the backflow at the draft tube outlet and the vortices in the impeller and guide/stay vanes are promoted or suppressed owing to the acceleration and deceleration of the fluid. This contributes to the difference in pump performance characteristics of the pump turbine. [ABSTRACT FROM AUTHOR]

Small-scale aquaculture is an important source of income and food in many developing countries. However, yields from many aquaculture ponds can be limited due to the lack of dissolved oxygen (DO). In the developed world, aeration systems are employed to increase stocking density and yields. However, these systems are expensive and energy intensive, putting them out of reach for farmers in many developing countries. This paper describes a new Wind Powered Aeration (WPA) concept, which can improve DO content in small-scale fish ponds. The WPA concept consists of a Vertical Axis Wind Turbine (VAWT) coupled to a sub-surface impeller. The impeller pulls water from the pond bottom to the surface through a draft tube. This introduces circulation, limiting DO losses and improving overall DO content. This paper presents the concept and models used to understand the performance. An experimentally validated computational fluid dynamics (CFD) model was used to enhance a bench-scale version of the impeller. The performance for the full-scale device was then estimated using CFD. These CFD results were used in a DO model to estimate the device impact. Results showed the WPA system could increase the overall DO content by 48%. This demonstrates the approach has the potential to improve DO and yields for small-scale aquaculture. • The WPA systems can increase DO levels for smallholder fish farmers. • Initial field test showed the WPA system increases DO levels 52%. • Lab experiments show the WPA system increases O2 transfer rate from atmosphere. • The WPA system creates a uniform DO distribution in fish ponds. • The VAWT model showed the system can operate for low wind speeds. [ABSTRACT FROM AUTHOR]

Many Modifications have been studied for classical Savonius wind turbines in the blade shape to improve the power efficiency. Four rotor blade modifications have been studied in the present study: classical, elliptical, using Fluent Adjoint solver and a novel blade design. Moreover, the influence of shaft, overlap ratio and blades number were conducted. Two dimensional CFD simulation is compared with the experimental data by using four turbulence models to determine the suitable models. The results of power efficiency indicate that the k- ε realizable turbulence model is more accurate when compared with the other models. The novel blade design showed better performance than other used modifications. [ABSTRACT FROM AUTHOR]

Copyright of DYNA - Ingeniería e Industria is the property of Publicaciones Dyna SL and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Harnessing the wind energy effectively and efficiently, to fulfil the ever increasing energy demands, has long been an area of active research. This research study is aimed at exploring the blade design of a small-to-medium sized Savonius type Vertical Axis Wind Turbine (VAWT) for urban applications, as the published research in this area is severely limited. A commercial Computational Fluid Dynamics (CFD) based solver has been used to numerically simulate airflow around a conventional (cup-shaped) 2-bladed VAWT over a wide operational range (i.e. Tip Speed Ratio (TSR) from 0.4-1) in order to identify the peak performance point. Blade tapering has been shown to affect the performance of a wind turbine. As such, in the present study, three different VAWT configurations have been used with blade tapering corresponding to Delta, Rhomb and Cross shaped blades. It has been observed that tapering the blades of a Savonius VAWT significantly reduces the torque coefficient of the turbine, while there is a slight decrease in the power coefficient. Comparing the three tapered blade configurations, the delta blades depict higher performance than the competitor designs. [ABSTRACT FROM AUTHOR]

Abstract VAWTs benefit from constructive coupling effect that significantly improves efficiency. This work aims at optimizing the configuration of turbine clusters with three Savonius turbines. To maximize the aggregate power output of a turbine cluster, two-dimensional (2D) computational fluid dynamics (CFD) is utilized, along with an evolutionary based Genetic Algorithm (GA). Four scenarios are investigated considering different combinations of rotational directions. For the optimal cluster obtained, a highest 37% increase in averaged power coefficient ( C P ¯)over an isolated Savonius turbine is achieved at Tip Speed Ratio (TSR) = 0.8. The substantial increase in efficiency for turbines in the optimal cluster is essentially due to constructive coupling in the flow field. Two major effective coupling mechanisms are proposed based on flow structures to explain the observed performance increase. Furthermore, a method to expand the optimal cluster into compact wind farms is proposed. It is verified that for a compact Savonis-type VAWT wind farm that consists of 12 turbines, a 30% increase in C P ¯ is obtained, showing the practicality of constructing efficient VAWT wind farms in areas with limited land. [ABSTRACT FROM AUTHOR]

Abstract The present study introduces a new relation to evaluate the equilibrium induced air velocity in the mid plane between the upstream and downstream rotor zones to give a good improvement in prediction of the maximum power coefficient. The relation is derived as a function of both interference factor in upwind and downwind rotor zones determined using classical DMST model. The root-finding algorithm is used to obtain the interference factor both in upwind and downwind zones of the turbine at each streamtube. The comparison between the numerical results and the experimental data of 5-m, 17-m, and 34-m Darrieus VAWTs shows that the use of the introduced relation gives a sensible improvement in the prediction of maximum value for turbine power coefficient. A theoretical study is presented based on the use of well documented symmetrical NACA0012 turbine blade profile. The effect of wind speed and rotor solidity on maximum power coefficient and corresponding optimal speed ratio on the turbine rotor is evaluated in order to determine an improved aerodynamic configuration for a given application. [ABSTRACT FROM AUTHOR]

Abstract The performance of a hybrid hydrokinetic turbine rotor under different operating conditions is investigated in this study. The effects of radius ratio and attachment angle on the power coefficient, self-starting capability and flow behavior around the turbine were simulated using commercially available software, ANSYS, with FLUENT as the solver. Realizable k -ε turbulence model has been used to solve the unsteady Reynolds-Averaged Navier-Stokes (URANS) equations. We compared the performance of a hybrid hydrokinetic turbine with the identically designed hybrid wind turbine under similar input power conditions. The hydrokinetic turbine rotor showed better performance than that of wind turbine rotor. The maximum values of coefficient of power (C P) and torque (C T) occur at attachment angles of 30° and 60° for a radius ratio of 0.2. At an attachment angle of 90°, fluctuations in C T were minimized. Highlights • Effects radius ratio and attachment angle are investigated. • Water velocity is considered in the range of 0.5 m/s to 2.5 m/s. • The performance and torque characteristics of the turbine are discussed. • An optimized set of parameters attain a maximum power coefficient as 0.34. [ABSTRACT FROM AUTHOR]

Savonius vertical axis wind turbines (VAWTs) typically suffer from low efficiency due to detrimental drag production during one half of the rotational cycle. The present study examines a stator assembly created with the objective of trapping cylindrical flow for application in a Savonius VAWT. While stator assemblies have been studied in situ around Savonius rotors in the past, they have never been isolated from the rotor to determine the physics of the flow field, raising the likelihood that a moving rotor could cover up deficiencies attributable to the stator design. The flow field created by a stator assembly, sans rotor, is studied computationally using three-dimensional (3D) numerical simulations in the commercial computational fluid dynamics (CFD) package Star-CCM+. Examination of the velocity and pressure contours at the central stator plane shows that the maximum induced velocity exceeded the freestream velocity by 65%. However, flow is not sufficiently trapped in the stator assembly, with excess leakage occurring between the stator blades due to adverse pressure gradients and momentum loss from induced vorticity. A parametric study was conducted on the effect of the number of stator blades with simulations conducted with 6, 12, and 24 blades. Reducing the blade number resulted in a reduction in the cohesiveness of the internal swirling flow structure and increased the leakage of flow through the stator. Two unique energy loss mechanisms have been identified with both caused by adverse pressure gradients induced by the stator. [ABSTRACT FROM AUTHOR]