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![Comparison analysis of experimental and computational (a) lift curves and (b) drag polars for the FB-3500-0050 airfoil with a trailing edge thickness of 8.75% [37].](publication/270079717/figure/fig1/AS:1088881084629012@1636620889645/Comparison-analysis-of-experimental-and-computational-a-lift-curves-and-b-drag-polars.jpg)
Comparison analysis of experimental and computational (a) lift curves and (b) drag polars for the FB-3500-0050 airfoil with a trailing edge thickness of 8.75% [37].
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Wind energy is one of the most promising renewable energy resources, and an increasing interest arises to develop straight-bladed vertical axis wind turbines (S-VAWTs), which offer a feasible solution for climate change and energy crisis. S-VAWTs have distinct advantages over horizontal axis wind turbines; however, more efforts should be devoted to...
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Citations
... For the influence of wake, the tip vortex intensity of the leading edge tip was the relatively lowest. Islam et al. [41] and Liang et al. [42] suggested that fabricating the blade tip in elliptic shape could reduce the induced drag. The elliptic blade tip shortens the chord near the tip so that the entire blade experiences an equivalent downwash, which improves the aerodynamic performance by increasing the Oswald efficiency number. ...
... This elliptic tip design was first seen in aircraft in the last century. However, Islam et al. [41] and Liang et al. [42] did not perform calculations on the elliptic tip, only analyzed its feasibility in VAWT blades. Moreover, they concluded that one of the primary barriers of elliptic tips for VAWT is the compound curves, which makes the blades more expensive. ...
... The endplate is a surface installed on the blade tip vertical to the spanwise direction, and is widely used in airfoil experiments. It functions to block the blade tip vortex caused by the pressure difference between the pressure and suction sides, thus forcing the aerodynamic performance of the blade tip behave like a two-dimensional airfoil [42]. Endplates do not significantly change the blade tip shape, and can even be applied to manufactured blades. ...
Vertical axis wind turbines are receiving renewed attention due to the challenges faced by horizontal axis wind turbines in recent years. To achieve commercial applications, a key aspect is to improve the relatively low power coefficient of vertical axis wind turbines. Among several factors that affects output efficiency, the three-dimensional tip loss effect is essential because each vertical axis wind turbine blade has two tops (e.g., the H-type wind turbine). Although several blade tips have been designed, a comprehensive and fair analysis is necessary to find a suitable one. Therefore, in this paper, a total of 20 blade tips have been analyzed using the three-dimensional computational fluid dynamic method. The results indicate that the improved winglet and endplate we proposed are relatively optimal when the synthetic performance of aerodynamic efficiency, structural loads and start-up torque is considered. However, the improvement mechanisms of these two tips are different. Based on the performance curves and the fluid fields at specific tip speed ratios, we find that the endplate increases the blade torque in the upwind region by reducing the spanwise flow, but its negative effect in the downwind region partially counteracts the improvement. For the improved winglet, it reduces the tip loss in the upwind region and suppress separation in the downwind region at the appropriate tip speed ratio, thus significantly improving its performance in one rotor revolution. The winglet also contributes to the reduction of rotor thrust. In addition, the influence of the blade tip on wake is not remarkable and is mainly concentrated in the tip area affected by the tip vortex.
... Features NACA profile[14] ...
Francis turbines are widely used in hydroelectric power plants all over the world, Ecuador is not an exception to this trend. Hence, Francis turbine design and assessment have taken importance in order to provide in-house design methods to enhance their performance in the region. The volcanic nature of the region facilitates sediment formation, which produces drastic erosion problems in many Francis turbines. Since guide vanes set the inlet flow velocity of the runner and erosion is related with the velocity distribution through this latter, this work evaluates guide vane profiles using a quasi-two dimensional approach to assess the impact of guide vane design on erosion rate. For this aim, parametric analysis and a mean line analysis are employed for the conceptual geometrical design, which then is coupled with a panel vortex model to assess the two dimensional hydro profiles for the guide vanes. Thus, the velocity triangles at entry and exit of the guide vane-runner setup can be related to the erosion rate within the runner. At this stage the calculations were carried out at the BEP and for the validation experimental data from the San Francisco hydroelectric power plant was used. The results show how the model developed captures main performance trends and enables the correlation of erosion with the geometrical features of the guide vanes. The method used is accurate enough for preliminary design and its low computational resources with versatility make it suitable for optimization routines for erosion proof designs.
... To generate higher torque from a blade, the pressure difference between the pressure side (extrados) and suction side (intrados) of the airfoil must be as larger as possible, with the flow smoothly translated without separation from the airfoil surface [4]. The features of an airfoil's geometry [23]. ...
... The structural model of the blade was considered as a simply supported beam, Fig. (16). Liang et al. [23] have presented the bending moment and deflection equations of this model as follows: ...
Vertical-axis wind turbines are resurfacing, especially in the
residential and small-scale power generation units. In 2020, the
global market of vertical-axis wind turbines (VAWTs) has
grown by about 4.4% CAGR (Compound Annual Growth Rate)
over the last few years with a 12.6 billion USD market by 2019.
The number of patents related to VAWTs has increased by
500% over the 10 years from 2009 to 2019. This requires an
interest concerning design considerations and multidisciplinary
analysis. In this paper, a 3-kW Darrieus H-rotor turbine
configuration is studied using a one-way fluid-structure
interaction-coupling, under three different wind conditions, to
investigate the stresses and displacements occurring to its
blades. Furthermore, the power-output difference under various
wind speeds and air densities is demonstrated. The paper also
involves the implementation of BEM (Blade Element
Momentum) codes such as Qblade to study the aerodynamic
parameters affecting the turbine operation. This study uses a
spar-supported blade instead of the horizontal webs that are
usually used.
... Where, 'n' represents number of turbine blades, 'c' represents chord length of airfoil, and 'D' represents the diameter of turbine blade. A turbine consisting of three blades has better self-starting ability (Bin et al. 2014) and low torque ripple (Beri and Yao 2011) than a turbine consisting of two blades, hence it is considered in the present investigation. The design parameter details of the studied turbine blades and attachments are given in Table 1. ...
Wind energy is a significant source of renewable energy and vertical axis wind turbine (VAWT) is one of the advanced wind energy harvesters. Maximum extraction of energy from wind harvesters is a major goal. Researchers are faced with the challenge of enhancing the performance of VAWTs in low wind speed conditions. To this end, researchers have contributed substantially by doing research on the blade design parameters thereby generating innovative and improved VAWT designs. However, there is hardly any work on the performance augmentation of H-Darrieus VAWT with blade attachments on asymmetric blades, which is the main objective of this work. Further, this work investigates the combined effect of turbulence intensity and flow dissimilarity on turbine performance for low wind speed condition. In this paper, blade attachment of length 20 cm (equal to 1/2.5 times blade span) is attached to asymmetric NACA 63–415 blade turbine having fixed blade pitch angle (+5°). NACA 63–415 blade profile is one of the prominent asymmetric series of NACA blades; hence it is considered in this work. The performances of seven different configurations of the turbine with blade attachments have been investigated experimentally at 5.0 m/s and 6.0 m/s using wind tunnel testing. The performance of the VAWT design is systematically improved by changing the number and position of these attachments on the turbine blades. The result shows that both side attachments on turbine blade on its top position have maximum power coefficient (Cp) of 0.13 at tip speed ratio (TSR) 1.8 at wind speed 6.0 m/s among all the turbine configurations tested. There is an improvement of power coefficient by 4.34% when attachments are placed at top of the turbine blade compared to turbine blade without attachment at wind speed 6.0 m/s. Further, maximum power coefficient is increased by 3.28% when turbine is operated from 5.0 m/s to 6.0 m/s for both side attachments at top of the turbine blade. Moreover, due to the combined effect of turbulence intensity and flow dissimilarity, the power coefficient of the turbine configuration having both side attachments has also improved a little. In this case, an improvement of 0.6% in power coefficient of turbine having both side attachments on top of the blade is achieved. As the turbine is a prototype having smaller size hence the effect of turbulence intensity and flow dissimilarity is less, in case of actual turbine of bigger size the effect of turbulence intensity and flow dissimilarity will be more and hence the percentage enhancement of power coefficient will also be more. Hence, it can be concluded that a turbine blade with higher degree of thickness (by using blade attachments) at top portion will increase the performance of an asymmetric blade H-Darrieus VAWT.
... The geometric parameter of the blade's aerofoil(Liang et al., 2014) ...
Wind energy is one of the most promising alternative energy sources for the continuously increasing demand for worlds’ energy consumption. In recent decades, there has been a steady and growing demand for energy, which has led to a shift to renewable resources. During many decades the wind turbine design, in particular, wind turbine blade design has been intensively researched to extract maximum possible energy from the wider range of wind flows. However, there have been many unresolved problems in the performance of small wind turbine blades due to insufficient energy generation at low-velocity wind regimes. Therefore, this project will investigate methods to improve the performance of small horizontal axis wind turbines (sHAWT) operating in low wind speed sites.
The primary cause for the reduction in energy generation at low wind velocity regimes was identified as the flow separation. In this project, suction and blowing techniques were used as active flow controls (AFC) to reduce flow separation in order to overcome the effect of an adverse pressure gradient (APG) and thus improve aerofoil performance. The data for a sHAWT with a 10 m diameter and a capacity of 25 kW were adopted. Two types of aerofoils were used, S823 and S822 aerofoils. Lift and drag coefficients were obtained with/without AFC technology. The range of tested angles of attack was between 0 and 21° and therefore considered suitable for predicting turbine performance. Suction speeds were changed to improve aerofoil performance, with -5 and -35 m/s suction speeds determined for low (less than 9°) and high (at least 9°) angles of attack respectively.
The research concluded that the deterioration of aerodynamic properties occurs at an AoA of 18°. It was also found that applying suction at 18% of the chord length on the upper surface gave good results at all angles of attack. The use of a boundary layer suction method delays the flow separation from the upper surface of the blade's aerofoil and even prevents separation for all but the highest angles of attack. The purpose of this method is to reduce the momentum flow in the high-pressure areas of the suction surface of the aerofoil. Although the use of such technologies may improve the performance of wind turbines, many challenges (such as design, maintenance and construction costs) must be met to reduce or mitigate the occurrence of separation in the boundary layer.
Moreover, the research found that the enhanced sHAWT operated very efficiently at a rotational speed of 60 and 110 rpm with lower/ higher wind speeds than 9 m/s respectively. The rates of improvement were variable with each wind speed, so the average rate of improvement was 15% as a result of using the early suction (S1) technique. The research also demonstrated that the annual energy production for a site with an average annual wind speed of 6 m/s is 22% higher compared to the selected standard wind turbines.
... For outward pitch angle, it is Ψ = α + β and for inward pitch angle the same is Ψ = α − β, where α is the angle of attack and β is the blade pitch angle. A three-bladed H-Darrieus turbine design is considered, which has better aerodynamic characteristic and self-starting capability [44]. The outline of NACA 63-415 airfoil having t/c = 0.3 with different fixed blade pitches is shown in Fig. 1b. ...
An asymmetric blade vertical-axis wind turbine (VAWT) is one of the emerging technologies for harvesting power in the built environment, which has low wind speed. Although asymmetric blade improves VAWT’s performance, the effect of blade pitch angle on its design is hardly ascertained. In this paper, unsteady 2D Reynolds-averaged Navier–Stokes CFD simulations are carried out to investigate the effect of blade pitch angle on the aerodynamic performance of a NACA 63-415 asymmetric blade H-Darrieus VAWT at a low wind speed of 6.0 m/s. Its detailed flow physics at different operating and pitch angle conditions is investigated, and important performance insights are obtained to elucidate its desired blade pitch for performance improvement. The present study shows that positive pitch angle (+ 5°) improves the turbine performance in upwind position, whereas negative pitch angle (− 5°) augments the turbine performance in downwind position as well as causes less wake effect than positive pitch angle. Further, optimal pitch angle (+ 5°) is found out at which the maximum power coefficient of 0.271 is obtained for an operating tip speed ratio 2.4. The present study delineates how desired blade pitch improves the performance of asymmetric blade VAWT for sustainable power generation in the built environment.
... In designing this S-VAWT, it is necessary to pay attention to several aspects, namely the selection of the blade by considering its aerodynamics and thickness, leading / trailing edge, and roughness as well as supporting arm, swept area, and solidity. Researchers in maximizing the power coefficient of the right rotor selection [14]. Researchers also propose a reduction in roughness on the blade surface, this contributes greatly to the dynamic stall. ...
Vertical Axis Wind Turbine is one of the most widely developed Renewable Energy. Many experiments and research are conducted to obtain maximum power efficiency. To get the maximum energy conversion efficiency required TSR (Tip Speed Ratio) is constant. To have the efficiency controller to change the Angle of Attack is required to maintain maximum efficiency at any wind speed. The method is applying controlled blades (aileron), the blades represent the value of Angle of Attack. In accordance with the changing of wind speed. In the VAWT Darrieus TSR reference value of 6, this value becomes the reference to obtain maximum efficiency against changes of wind speed. PID method is used to control the blades to form an Angle of Attack corresponding to the dynamic changes in wind speed. So that the VAWT speed is used as feedback into control. The shape of the blade affects the efficiency of the resulting spin, therefore the most efficient blade of the blades is the thin airfoil family in order to obtain the maximum flow of wind to rotate the generator. From the simulation done by using VAWT, it can be shown that the power efficiency obtained up to 28% in any wind speed.
... A medida que se aumenta la solidez de la turbina el rango de operación de TSR de la turbina comienza desplazarse hacia la izquierda, es decir se comienza a aprovechar más el viento para velocidades muy altas (Lian, Zhang, Li, Liu, & Yang, 2014), lo cual en el caso de presente trabajo. ...
... Tabla 5.6. Comparación de las configuraciones para los soportes del álabe (Lian, Zhang, Li, Liu, & Yang, 2014) Patrones ...
... Inicialmente la turbina del estudio de CFD poseía una solidez de 0,150, sin embargo, al cambiar el radio la propuesta final tiene una solidez de 0,075. Estudios han sugerido que la solidez es un parámetro de diseño de una VAWT que desplaza el punto de operación de la misma, al aumentar la solidez, el TSR disminuye y por lo tanto la turbina es más eficiente para velocidades más altas, mientras que si disminuye, el TSR aumenta, haciendo posible operar en velocidades más bajas de viento(Lian, Zhang, Li, Liu, & Yang, 2014). Por lo tanto, se espera que el punto de operación de la turbina propuesta en la Tabla 4.1, desplace su punto de operación y modifique la curva de potencia. ...
En Venezuela, la Península de Paraguaná presenta velocidades de viento superiores a los 5 m/s a 10 metros sobre el nivel del suelo, que la convierte en una ubicación atractiva para instalar turbinas eólicas. El presente trabajo aborda el diseño mecánico de un aerogenerador de tipo Darrieus de perfiles rectos y simétricos, basado en una propuesta inicial dada por Banega (2016). Esta sugería un rotor con radio de 1,96 m con velocidad de giro de 120 rpm, con 3 álabes de perfil NACA0018 de cuerda 10 cm; capaz de entregar 0,39 kW para una velocidad de viento de 6 m/s. Mediante un programa de MATLAB se logró verificar la propuesta inicial y proponer un cambio de cuerda a 20 cm, debido a que no se mantenían las condiciones de operación estimadas en las simulaciones de Banega (2016). Además, el programa permitió estimar las cargas aerodinámicas para el diseño del rotor. Seguidamente, ya obtenidas las dimensiones generales de la turbina, se estudiaron las alternativas comerciales disponibles para el generador y se consideró un diseño propio. Posteriormente se generaron 3 propuestas de diseño conceptual y fueron evaluadas mediante una matriz de decisiones. Se decidió que la opción de fabricar el generador era la más acertada económica y técnicamente. Luego, se expone el diseño de detalle, mencionando las variables involucradas en el cálculo para el dimensionamiento de los distintos componentes, así como también la selección de materiales. Finalmente se brinda un presupuesto aproximado que permite estimar el costo de fabricación de la VAWT.
... The blade thickness effects for different sets of airfoils from different series have been investigated by (Danao, Qin, and Howell 2012). Several blade configurations (t/c = 15-25%) have been recommended based on different design and operational parameters (Dereng 1981;Liang et al. 2014;Seki 2005). Due to better stall characteristics, thicker airfoil has capability to perform better at high solidity (Ghasemian, Ashrafi, and Sedaghat 2017). ...
Vertical axis wind turbine (VAWT) is an economic and widely used energy converter for converting wind energy into useful form of energy, like mechanical and electrical energy. For efficient energy conversion in low wind speed and to have improved power coefficient of asymmetric blade VAWT, selection of optimum blade thickness is needed thus entailing its detailed investigation with respect to different operating wind speed conditions. Present study methodically explores the impact of thickness to chord (t/c) ratio on aerodynamic performance of a three bladed asymmetrical blade H-Darrieus VAWT at different low wind speed conditions by using 2D unsteady CFD simulations. The optimal t/c is obtained on the basis of maximum power coefficient and average moment coefficient of the turbine. The aerodynamic performance curves are obtained at different operating and t/c conditions and the performance insights are corroborated with the findings from the flow physics study to come to some concrete conclusions on the effects of the thickness to chord ratio. The present study identifies large blade curvature to create a large diverging passage on the blade suction surface as the prominent reason for aerodynamic performance drop at a high t/c ratio.
... The development of wind turbine plants in this study is part of the development of renewable energy hybrid plants with thermal biomass systems [3], and other biomass applications [4]. Investigation of rotor support and its influence on deflection and on turbine performance, with blade tips recommendations support and overhang support [5]. The shaft diameter can affect turbine performance due to shaft resistance and surface roughness [6]. ...
In a vertical hybrid turbine with a shaft bearing holder on one side, it has a shaft deflection problem that interferes with turbine performance. This study aims to improve the design of the turbine holder. The methodology used in this study is to analyse the deflection behaviour of the turbine when rotating. Next in the turbine design review, and the result is to increase the distance of the shaft holder bearings and increase the bearing diameter in the triangular frame. Deflection testing with the help of tracker software that’s able to measure deflection distance in one field when the shaft rotates. The results of the deflection comparison before and after the design improvement show a significant deflection reduction.
