Small Vertical Axis Wind Turbine Research Articles

Parametric study of the dual vertical axis wind turbine using CFD

The Dual Vertical Axis Wind Turbine (D-VAWT) is an innovative turbine proposed to improve the aerodynamic efficiency of small Vertical Axis Wind Turbines (VAWTs). The D-VAWT has two axes, allowing the blades to move in an oval shaped path to extend the region of maximum power generation of a typical VAWT. The aim of this paper is to perform a parametric study on the D-VAWT variables as a previous investigation aimed only to prove its concept. The current study is performed through 2D unsteady simulations using computational fluid dynamics. Advanced moving mesh techniques are used to prescribe the motion of the blades, combining the sliding and dynamic mesh techniques as well as re-meshing for multi-blade simulations. A turbine with a single blade is first investigated to determine the relation between the tip speed ratio (TSR) and power coefficient. The investigation continues with the study of the turbine sensitivity to different incoming wind angles, turbine axes spacing, number of blades, airfoil profile and blade mounting point. It was found that the D-VAWT has a low sensitivity to TSR, allowing the turbine to operate efficiently for a wide range of TSRs.

CFD simulations of power coefficients for an innovative Darrieus style vertical axis wind turbine with auxiliary straight blades

The increasing price of fossil derivatives, global warming and energy market instabilities, have led to an increasing interest in renewable energy sources such as wind energy. Amongst the different typologies of wind generators, small scale Vertical Axis Wind Turbines (VAWT) present the greatest potential for off grid power generation at low wind speeds. In the present work, Computational Fluid Dynamic (CFD) simulations were performed in order to investigate the performance of an innovative configuration of straight-blades Darrieus-style vertical axis micro wind turbine, specifically developed for small scale energy conversion at low wind speeds. The micro turbine under investigation is composed of three pairs of airfoils, consisting of a main and auxiliary blades with different chord lengths. The simulations were made using the open source finite volume based CFD toolbox OpenFOAM, considering different turbulence models and adopting a moving mesh approach for the turbine rotor. The simulated data were reported in terms of dimensionless power coefficients for dynamic performance analysis. The results from the simulations were compared to the data obtained from experiments on a scaled model of the same VAWT configuration, conducted in a closed circuit open chamber wind tunnel facility available at the Laboratory of Industrial Measurements (LaMI) of the University of Cassino and Lazio Meridionale (UNICLAM). From the proposed analysis, it was observed that the most suitable model for the simulation of the performances of the micro turbine under investigation is the one-equation Spalart-Allmaras, even if under the conditions analysed in the present work and for TSR values higher than 1.1, some discrepancies between numerical and experimental data can be observed.

Influence of the vertical wind and wind direction on the power output of a small vertical-axis wind turbine installed on the rooftop of a building

The goal of this study is to investigate the performance of a small vertical-axis wind turbine at an environment with the turbulence intensity more than 30%, particularly on the influence of the vertical wind, the vertical angle, the wind with the unknown direction, the horizontal wind speed, and the turbulence intensity on the power output, which are seldom reported before. The results show that more than 90% of the power is generated when the vertical angle is less than or equal to 45°. The vertical wind speed has the obvious influence on the power when the horizontal wind speed is between 5m/s and 8m/s. The percentage of the power generated by the wind with the unknown direction decreases from 31.1% to 8.4% as the horizontal wind speed increases from 4m/s to 9m/s. The efficiency is over 40% only when the horizontal wind speed is over 8m/s. The higher turbulence intensity increases the power at the lower wind speed, but decreases the power at the higher wind speed. Furthermore, the results can be used asa reference for the improvement of aerodynamic characteristics, efficiency, CFD simulation and the location selection of a vertical-axis wind turbine.

Development of the Dual Vertical Axis Wind Turbine Using Computational Fluid Dynamics

Small vertical axis wind turbines (VAWTs) are good candidates to extract energy from wind in urban areas because they are easy to install, service, and do not generate much noise; however, the efficiency of small turbines is low. Here-in a new turbine, with high efficiency, is proposed. The novel design is based on the classical H-Darrieus VAWT. VAWTs produce the highest power when the blade chord is perpendicular to the incoming wind direction. The basic idea behind the proposed turbine is to extend that said region of maximum power by having the blades continue straight instead of following a circular path. This motion can be performed if the blades turn along two axes; hence, it was named dual vertical axis wind turbine (D-VAWT). The analysis of this new turbine is done through the use of computational fluid dynamics (CFD) with two-dimensional (2D) and three-dimensional (3D) simulations. While 2D is used to validate the methodology, 3D is used to get an accurate estimate of the turbine performance. The analysis of a single blade is performed and the turbine shows that a power coefficient of 0.4 can be achieved, reaching performance levels high enough to compete with the most efficient VAWTs. The D-VAWT is still far from full optimization, but the analysis presented here shows the hidden potential and serves as proof of concept.

Effect of airfoil and solidity on performance of small scale vertical axis wind turbine using three dimensional CFD model

This paper presents a study on the effect of solidity and airfoil profile on the performance of Vertical Axis Wind Turbines (VAWTs). A 1.1 kW commercially viable Darrieus VAWT was studied using ANSYS Fluent. Four different airfoils – NACA 0012, NACA 0015, NACA 0030 and AIR 001 – were considered in the analysis. The tip speed ratios (λ) were varied from 1 to 2.5 with an incoming wind velocity of 10 m/s. It was observed that NACA 0030 performed better at lower values of λ due to long duration of attached flow; while NACA 0012 performed better at λ > 1.8 with a wider range of λ. The shed vortex dissipates much faster for thinner airfoils than for thicker airfoils at higher values of λ. Two bladed VAWTs generated more power than the three bladed turbines. This indicated that turbines with lower solidity perform better at high λ.

Characterization of a new open jet wind tunnel to optimize and test vertical axis wind turbines

Based on the increasing interest in urban environmental technologies, the study of small scale vertical axis wind turbines shows motivating challenges. In this paper, we present the characteristics and potentials of a new open jet wind tunnel. It has a nozzle exit area of 1.5 × 1.5 m2, and it can be operated with exit velocities from 3 m/s to 17 m/s. The characterization of the flow has been carried out with calibrated pitot tubes, cup anemometers, and hot wire anemometers. Two different configurations of the test area, with and without a ceiling, are considered. Measurements in the range of available exit velocities show that the cross section, where the velocity and turbulence intensities show an acceptable level of uniformity, has an area of 0.8 × 0.8 m2 and a streamwise dimension of 2 m from the nozzle exit of the tunnel. In this working section, the maximum turbulence intensity is 4%. The detailed characterization of the flow carried out indicates that the wind tunnel can be used to test small scale models of wind turbines.

Determination of performance parameters of vertical axis wind turbines in wind tunnel

The paper deals with the determination of the performance parameters of a small vertical axis wind turbines (VAWT), which operate by the utilization of drag forces acting on the blades of the turbine. The performance was evaluated by investigating the electrical power output and torque moment of the wind machine. Measurements were performed on the full-scale model and the experimental data are assessed and compared to other types of wind turbines, with respect to its purpose.

Wind Tunnel testing of small Vertical-Axis Wind Turbines in Turbulent Flows

This study presents an innovative wind tunnel approach to evaluate the efficiency of Vertical-Axis Wind Turbines (VAWT) in turbulent flows, to study their integration in urban environments.The first part of the research is devoted to obtaining highly-turbulent wind profiles in the wind tunnel, with the use of different configurations of square grids. A careful study and validation of this technique is done, in order to obtain uniform wind conditions with the adequate values of turbulence intensity and length scales to model the urban flows.The set-up is used to test a H-Darrieus VAWT under values of turbulence over 5%, in comparison with the operation of the turbine under free stream. The preliminary results show that high levels of turbulence do have a significant effect in turbine performance, causing a drop of power for high rotational speeds, increased vibrations in the structure and more difficult control of the rotor. More tests are advised to validate these observations, as well as to expand the study over higher values of turbulence intensity, in order to present a more detailed study with empirical conclusions.

Design, construction and study of small scale vertical axis wind turbine based on a magnetically levitated axial flux permanent magnet generator

A small scale vertical axis wind turbine (VAWT) with axial flux permanent magnet (AFPM) generator is designed and the magnetic levitation method is used to increase the efficiency of this type of wind turbine. Magnetic levitation is inserted by using rare earth permanent magnets, the repelling force of magnets are used to suspend the rotating part of both the turbine and generator. Moreover, this design of simple generator which can easily drive without a geared mechanism, lessen cost and the complexity of the system by reducing the quantity of driving components. Three phase output is obtained from the designed generator which is converted into direct current through a three-phase rectifier to charge the batteries. The performance of proposed prototype is also tested experimentally. From the results it is found that the designed wind turbine performs optimally and efficiently as predicted by the developed design process.

Wind tunnel testing of scaled models of a newly developed Darrieus-style vertical axis wind turbine with auxiliary straight blades

Renewable sources of energy, needed because of the increasing price of fossil derivatives, global warming and energy market instabilities, have led to an increasing interest in wind energy. Among the different typologies, small scale Vertical Axis Wind Turbines (VAWT) present the greatest potential for off grid power generation at low wind speeds. In the present work, wind tunnel investigations about the performance of an innovative configuration of straight-blades Darrieus-style vertical axis micro wind turbine, specifically developed for small scale energy conversion at low wind speeds, has been made on scaled models. The micro turbine under investigation consists of three pairs of airfoils. Each pair consists of a main and auxiliary airfoil with different chord lengths. A standard Darrieus configuration, consisting of three single airfoils, was also tested for comparison. The experiments were conducted in a closed circuit open chamber wind tunnel facility available at the Laboratory of Industrial Measurements (LaMI) of the University of Cassino and Lazio Meridionale (UNICLAM). Measured data were reported in terms of dimensionless power and torque coefficients for dynamic performance analysis and static torque coefficient for static performance analysis. The adoption of auxiliary airfoils has demonstrated to give more dynamic torque at the lower wind speeds with respect to a standard Darrieus rotor, resulting in better performance for all the wind speeds considered. In terms of dynamic power coefficient, the standard Darrieus configuration presented slightly better performance for the highest wind speed analyzed. The proposed configuration showed also an higher value of static torque coefficient with respect to the standard Darrieus micro turbine, resulting in a better self-starting ability.

Effect of Boundary Layer Tripping on the Aeroacoustics of Small Vertical Axis Wind Turbines

Small wind turbines are investigated as a possible solution for using wind energy at small scales in urban and suburban areas. Most turbines are suffering from a low aerodynamic performance due to turbulent and complex wind situations in cities. Therefore, increasing aerodynamic performance and reducing noise is an important factor to design small wind turbines. In order to optimize such turbines with respect to noise and efficiency it is important to understand the physical mechanisms. Measuring acoustic in urban environment it is hardly possible to obtain reproducible results, which are necessary for a comprehensively and profoundly investigation. Therefore, experimental studies have to been performed in anechoic wind tunnels. Those tunnels are mostly limited in size, which makes it quite difficult to investigate full small wind turbine models. Hence a model scale has to be used in order to measure the power and acoustic performance. For comparing the model scale results with original turbines, the same flow conditions around the airfoils are necessary. Due to the smaller size of the model scale the relative velocities of the blades are less, which can result in a laminar boundary layer. In order to force transition from laminar to turbulent, boundary layer trips can be used. The focus of this study is to examine and quantify the effect of boundary layer tripping on the aeroacoustics in case of small vertical axis wind turbines.

Analysis of Different Blade Architectures on small VAWT Performance

The present paper aims at describing and comparing different small Vertical Axis Wind Turbine (VAWT) architectures, in terms of performance and loads. These characteristics can be highlighted by resorting to the Blade Element-Momentum (BE-M) model, commonly adopted for rotor pre-design and controller assessment. After validating the model with experimental data, the paper focuses on the analysis of VAWT loads depending on some relevant rotor features: blade number (2 and 3), airfoil camber line (comparing symmetrical and asymmetrical profiles) and blade inclination (straight versus helical blade). The effect of such characteristics on both power and thrusts (in the streamwise direction and in the crosswise one) as a function of both the blades azimuthal position and their Tip Speed Ratio (TSR) are presented and widely discussed.

The influence of flow field and aerodynamic forces on a straight-bladed vertical axis wind turbine

This paper has attempted to compile the assessment of flow field and aerodynamic forces acting on a small straight-bladed vertical axis wind turbine (VAWT). Two dimensional unsteady flows around the VAWT, operating at three different tip speed ratios in a wind tunnel, were investigated through the use of a Laser Doppler Velocimeter (LDV) system. Furthermore, in order to explicate the characteristics of aerodynamic forces, pressures acting on the blade surface were measured during the rotation by a multiport scanner mounted on the hub and pressure signals were transmitted to the stationary system through a wireless LAN. Velocity distribution proved the wind velocity deficit. While, the geometrical angle of attack and resultant flow velocity change periodically due to local wind velocity and direction depending on the azimuth angle. The power coefficient, tangential force, lift and drag which are obtained by pressure distribution are discussed as a function of blade azimuthally position, achieving a numerical quantification of the influence of tip speed ratio on overall rotor performance. As a result, it is clarified that aerodynamic forces show the maximum values when the blade passes through the upstream region.

Performance prediction and fundamental understanding of small scale vertical axis wind turbine with variable amplitude blade pitching

This paper predicts and analyzes the aerodynamic performance of a Vertical Axis Wind Turbine (VAWT) with variable amplitude dynamic blade pitching. This study contributes to the physics based understanding of the dependence of power extracted by the turbine on various design parameters. An aerodynamic model based on double multiple streamtube theory coupled to an airfoil table lookup based blade element theory analysis and attached unsteady aerodynamics is used for performance prediction. A method for calculating virtual camber effect for dynamically pitching blades is proposed and validated. Inclusion of dynamic virtual camber effect and unsteady aerodynamics are critical for accurate performance prediction. The parametric study relates performance of VAWT to rotor solidity, blade airfoil and pitch amplitude. It is concluded that the amplitude of sinusoidal blade pitching must be varied with wind speed and tip speed ratio to maximize the power extracted from the turbine for wide range of wind speeds and tip speed ratios. High (about 35°) pitch amplitudes work best for tip speed ratios below 0.5 and the pitch amplitude should be reduced to approximately 10° for tip speed ratios greater than 2.0.

DESIGN, CONSTRUCTION AND STUDY OF SMALL SCALE VERTICAL AXIS WIND TURBINE BASED ON MAGNETICALLY LEVITATED AXIAL FLUX PERMANENT MAGNET GENERATOR

AbstractA small scale vertical axis wind turbine (VAWT) withaxial flux permanent magnet (AFPM) generator has beendesigned and magnetic levitation method is used toincrease the efficiency of this type of wind turbine [1].Magnetic levitation is inserted by using rare earthpermanent magnets, the repelling force of magnets areused to suspend the rotating part of both turbine andgenerator. Moreover, design of simple generator whichcan easily drive without geared mechanism, lessen costand the complexity of the system by reducing thequantity of driving components. Three phase output isobtained from designed generator which is converted intodirect current through three-phase rectifier to charge thebatteries. The performance of proposed prototype is alsotested experimentally. The turbine performs as predictedby the design process.

Structural Design Optimization of a Vertical Axis Wind Turbine for Seismic Qualification and Lightweight

Recently, there is a growing interest in seismic qualification of ridges, buildings and mechanical equipment worldwide due to increase of accidents caused by earthquake. Severe earthquake can bring serious problems in the wind turbines and eventually lead to an interruption to their electric power supply. To overcome and prevent these undesirable problems, structural design optimization of a small vertical axis wind turbine has performed, in this study, for seismic qualification and lightweight by using a Genetic Algorithm (GA) subject to some design constraints such as the maximum stress limit, maximum deformation limit, and seismic acceleration gain limit. Also, the structural design optimizations were conducted for the four different initial design variable sets to confirm robustness of the optimization algorithm used. As a result, all the optimization results for the 4 different initial designs showed good agreement with each other properly. Thus the structural design optimization of a small vertical-axis wind turbine could be successfully accomplished.

Influences of some parameters on the performance of a small vertical axis wind turbine

The effects of various parameters on the performance of a straight bladed vertical axis wind turbine, using the vortex model, have been numerically investigated. A vortex model has been used to evaluate the performance of a vertical axis wind turbine, by means of aerodynamic characteristics of different airfoils for Reynolds numbers between 105 and 106 . Parameters such as the thickness and the camber of the blade airfoil, the solidity, the type of blade profile, the number of blades and the pitch angle, which influence the power coefficient, C P , and the start-up regime. This study can be used in the designing an optimal vertical axis wind turbine in a specific location, when the prevailed wind regime is known.

Numerical study on small scale vertical axis wind turbine

The performance of a Vertical Axis Wind Turbine (VAWT) is numerically analyzed. The set-up is Hdarrieus with three straight blades airfoils NACA attached to a rotating vertical shaft. The wind turbine has solidity equals to the unity operating with wind velocity of 7 m/s. Influence of pitch angle is tested to get design tendencies. 2D, transient, Navier Stokes equations are solved using the code Ansys-Fluent. Conservation equations were solved with a Third-Order MUSCL scheme using SIMPLE to couple pressure and velocity. More than six revolutions must be simulated to get the periodic behavior. Two models of turbulence have been contrasted Realizable k-epsilon and Transition SST concluding the last one show more realistic flow features. Pitch angles of 0o, -6o and -10o have been tested with Tip Speed Ratios ranging from 0.7 and 1.6. The no null pitch angles improve the performance of the wind turbine. Instantaneous and averaged power coefficients as well as detailed flow field around the airfoils are showed.

Enhanced energy capture by a vertical axis wind turbine during gusty winds in an urban/suburban environment

Wind resource maps of annual-averaged wind speeds, typically used in the siting of wind turbines and wind farms, can grossly underpredict the actual wind energy potential in areas with highly transient or gusty winds. The goal of the present study is to quantify the additional energy capable of being harvested by a small vertical axis wind turbine using control strategies that exploit the excess energy in wind gusts. A transient-response numerical model is utilized with input from actual wind data acquired by cup-vane and sonic anemometers located in both an urban and suburban area. The total energy captured by the turbine during the year 2013, along with its overall efficiency, was determined for two different control strategies: constant rotational speed (ω) controller and ideal tip speed ratio (TSR) controller. For the case of the constant ω controller, the turbine achieves maximum efficiency when it is operated at an optimal overspeed setting, ωopt. Results indicate that ωopt can be estimated from the turbulence intensity of the wind. For the case of the ideal TSR controller, turbine efficiency was observed a plateau to a maximum value when the nondimensional turbine response parameter ζ dropped below a critical value ζc. This is as expected since turbines with fast response times (ζ < ζc) are capable of instantaneously tracking fluctuations in the wind and thus effectively capturing the high energy content contained within each wind gust. The value of ζc exhibits a dependence on the characteristic gust time scale. Over the course of the year, the turbine in conjunction with the constant ω controller, operating at ωopt, was capable of harvesting six times the energy of a naive controller operating a fixed ω based on the annual-averaged mean wind speed. The same turbine operating in conjunction with an ideal TSR controller, however, was successful in harvesting nearly thirteen times the energy of that with the naive controller. This may have significant implications on the viability of small turbines in relatively gusty urban/suburban areas, even when the annual-averaged wind speed is below a threshold typically considered practical for harvesting wind energy.

Analysis of conditions favourable for small vertical axis wind turbines between building passages in urban areas of Sweden

This paper presents the analysis of installing the vertical axis wind turbines between the building passages on an island in Stockholm, Sweden. Based on the idea of wind speed amplification due to the venture effect in passages, practical measurements were carried out to study the wind profile for a range of passage widths in parallel building passages. Highest increment in wind speed was observed in building passages located on the periphery of sland as wind enters from free field. Wind mapping was performed in the island to choose the most favourable location to install the vertical axis wind turbines (VAWT). Using the annual wind speed data for location and measured amplification factor, energy potential of the street was calculated. This analysis verified that small vertical axis wind turbines can be installed in the passage centre line provided that enough space is provided for traffic and passengers.