Enhancing vertical axis wind turbine by dynamic stall control using synthetic jets

The need for energy and electricity has been increasing globally, and this means more power is required from the power plants. Power plants, however, will then continue harming the earth because of the greenhouse gasses produced while generating energies that contribute to global warming. Using renewable sources to produce clean energies is one of the sustainable methods to deal with such challenges. Wind energy is one of the renewable sources, which is accessible anywhere on earth, creating green energy. Wind turbines are mainly categorized into Horizontal Axis Wind Turbines (HAWT) and Vertical Axis Wind Turbines (VAWT). This paper firstly presents a general comparison between the HAWTs and VAWTs. Then, it presents mathematical modelling for the aerodynamic factors of HAWT and Darrieus VAWT to assist the researchers to understand some key design aspects of wind turbines, such as lift/drag ratio, tip speed ratio, power coefficient, and torque coefficient. Also, this paper presents a review of the aerodynamic performance of the recent VAWT designs to help researchers to identify and choose the best model among the Savonius and Darrieus rotors for further development or designing a new model at different wind conditions. This comparison review shows that for a large scale HAWT upwind 3 bladed wind turbines are the most optimum. The helical Savonius rotors perform better by having positive torque coefficient at all azimuth angles. Moreover, helical Darrieus was found to produce lesser noise and suitable for conventional areas. hybrid Savonius-Darrieus rotors can solve the self-starting challenge of the VAWTs, and they are suitable at low wind speeds. At last, this review shows some of the recent hybrid Savonius-Darrieus rotors which would help to solve the low efficiency of Savonius rotor and self-starting challenge of Darrieus rotors.

I.IntroductionThe vertical axis wind turbine has been widely concerned because of its advantages such as multiphase wind, stable force, easy installation and maintenance, and small starting wind speed. Vertical axis wind turbines mostly use permanent magnet synchronous generators or doubly fed induction wind turbines, and most of them are axial flux permanent magnet generators[1]. Compared with doubly fed induction wind turbine, permanent magnet synchronous generator (PMSG) has the advantage of high power density and is the main research object of vertical axis wind turbine. However, the direct coupling of the high power axial flux permanent magnet synchronous generator and wind turbine causes the starting of the wind turbine to become more difficult. In order to improve the starting performance of vertical axis wind turbines, maglev technology is considered to reduce the starting resistance as the development direction of vertical axis wind turbines. Therefore, an asymmetric-primary axis-flux hybrid- electricity generator is proposed in this paper, and the decoupling control of levitation force and output power is implemented using asymmetric primary and hybrid excitation.II.operation principleThe proposed asymmetric-primary axis-flux hybrid-excitation generator for the vertical axis wind turbine structure is shown in the Fig.1.The generator is composed of double stator primary and single actuator. The double stator primary has an asymmetric structure design, and the rotor shaft is connected with the wind turbine shaft to realize direct drive wind power generation. The rotor adopts the spacing design of permanent magnet and modulating tooth to reduce the consumption of permanent magnet. Both the excitation winding and the armature winding are located in the primary stator, so the mixed excitation and magnetic field can be adjusted without adding any mechanism such as brush slip ring, which reduces the complexity of the structure.In general, the proposed generator has the following characteristics(1) The flat structure shortens the axial length of the generator and is suitable for direct drive of vertical axis wind power generation system.(2) The levitation force is provided by bilateral unbalance design of axial flux. The two sides adopt different primary sizes, and then the axial electromagnetic force imbalance of the bilateral air gap forms the suspension force, which avoids adding active and passive levitation mechanisms and reduces the complexity of the overall system.(3) The levitation force and output power are controlled by hybrid excitation. The primary tooth DC excitation is adopted to realize zero crosslinking of the excitation with permanent magnet and armature, and the levitation force regulation does not affect the output power. The system can start at low wind speed, and the levitation force and total output power can be adjusted according to the change of wind speed. Through free distribution of bilateral power to achieve the total power following the wind speed and the levitation force following the lift force of the wind turbine.(4) Using magnetic field modulated axial magnetic field structure, the rotor structure is simple and reliable. If the pole pair numbers of rotor and armature are pr and ps, and the number of the stator tooth is pn, there is pr = pn±ps. The design makes it have the magnetic field modulation effect, which can increase the magnetic field change rate under the low speed, thus increasing the generation power.(5) The use of concentrated armature windings and excitation windings reduces the end, thus reducing magnetic leakage and losses.III.simulation and resultsA three-dimensional finite element model of the asymmetric-primary axis-flux hybrid-excitation generator is established, and the no-load characteristics and load characteristics of the generator are obtained. The no-load characteristics under different excitation current are simulated, and the flux linkage of armature coils and DC excitation coils are shown in Fig.2.We can see that when different excitation currents are applied, the crossing flux linkage between DC excitation winding and secondary permanent magnet is almost 0, and DC flux has little effect on the armature flux. Therefore, When the excitation changes, the unilateral levitation force changes only in amplitude, but there is no harmonic phase shift, and positioning torque is almost unaffected. he proposed generator has good decoupling performance of levitation force, output power, and DC excitation. In addition, the optimization design of the generator is further studied such as pole arc coefficient, positioning moment and pole slot ratio. IV.conclusionIn this paper, we proposed an asymmetric-primary axis-flux hybrid-excitation generator, studied the no-load characteristics, load characteristics and excitation characteristics, and optimized the structural parameters of the generator. The simulation results are obtained, and state that the generator can realize the decoupling of the levitation force of excitation and power, which is suitable for vertical axis wind turbine. **

The vertical axis wind turbine (VAWT) with helical-blade has been developed, manufactured and applied in almost all developed countries. In Indonesia, vertical axis wind turbines are still not widely applied compared to horizontal axis wind turbines. Vertical axis wind turbines with helical-blade are still very rare in Indonesia. Research and development of the vertical axis wind turbine are needed because of its advantages compared to horizontal axis wind turbine. The advantages are: can operate in various wind directions, lower noise due to smaller tip speed ratio (TSR) and for large-scale, mechanical and electrical systems of turbine can be placed on ground. The aim of this research is to design a vertical axis wind turbine rotor with helical-blade that can be applied at low speeds and changing direction wind condition, such as urban wind characteristics. Performance analysis of wind turbine rotor is done by using double-multiple stream-tube (DMS) model approach. This research yields a rotor of vertical axis wind turbine with helical-blade with rotor length and diameter are 2m and 1m respectively, the rotor blade airfoil is DU-06-W-200 with chord length is 0.2m. From analysis, the optimum tip speed ratio of the rotor is 2.6 with a maximum power coefficient is 0.57.

This paper introduces the GWIT EHD VAWT and the logic and history behind its development. We develop a simplified model to compare the performance of EHD VAWTs with conventional propeller machines. GWIT is engaged on a path to optimize the performance of its wind turbines in a wind farm setting. The paper details the characteristics of its first two prototypes - JJ and JJ3. The turbines are designed to meet the atmospheric conditions prevailing in China. While the EHD VAWT concept can be implemented in many configurations, GWIT has developed its turbines to operate over the broadest possible atmospheric conditions with an absolute minimum of moving mechanical components. We focus on turbine designs that more than double energy capture from the wind site. More than 90% of the turbine's content is of local manufacture. I. HISTORY OF THE EHD VAWT Wind turbines can trace their origins thousands of years into the past. Modern wind turbines can trace their current mission - the conversion of wind energy into electricity-back to the closing days of World War II when some Northern Continental European nations first converted some of their water pumping and grain milling wind turbines into producers of electricity. Since that time European nations began to devote significant research efforts into developing efficient machines to produce grid usable electricity from their abundant wind resources. More recently these efforts have been joined by North American and Asian nations. While some effort was devoted to the development of vertical axis wind turbines (VAWTs) almost all European research efforts were devoted to horizontal axis wind turbines (HAWTs). In Canada and the United States significant efforts were made to develop VAWTs, but the vast majority of wind energy research was devoted to HAWTs. By 1980 European designed HAWTs were focusing on economic parameters while Canadian and American efforts were still attempting to demonstrate feasibility. Numerous HAWT powered wind farms emerged but only two VAWT powered wind farms were in development or operation. Rely- ing on a Sandia National Laboratories design, FloWind fielded 512 170 kW F-17 and 300 kW F-19 VAWTs on two wind farms in California. Both wind farms operated successfully until they were replaced with Micon HAWTs between 1998 and 2002.

Green energy harvester, known as wind turbine, able to convert mechanical works to electrical power. There are two main type of wind turbine that considered thoroughly, which are the horizontal and vertical axis wind turbine respectively. This project mainly focus on the design of new wind turbine that can operate well together in low wind speed condition in Malaysia. For the first stage of this project, the problems, purpose, and planning regarding with the project properly determined. Literature survey then furthered analyzed in order to know the wind power or behavior across the world, and specifically in Malaysia, research of turbine that can work in low wind speed condition, as well as parameter that often used in designing wind turbine by previous researcher. From the literature survey, the selected turbine was a Three-Bladed Savonius Wind Turbine, which is one type of Vertical Axis Wind Turbine (VAWT). That turbine will be attached to another VAWT turbine system to help generate more power and better performance. Design theoretical calculation and material selection have been properly analyzed before fabrication can be done. Upon completion of the fabrication, Savonius wind turbine section properly tested through experimental works by using simple wind tunnel in Faculty of Engineering Mechanical Workshop, and all readings and data collected using applicable tools and equipment. For the experimental works of Savonius rotor, the variable includes of blades curve angle from its center at different wind speeds. The data collected then interpreted through charts and graph for comparison and performance analysis, and conclude that 1200 blades curve angle from its center was the best among the other type of blades. From this project, it can be concluded that this type of mix wind turbine able to works in low wind speed condition in Malaysia, but a better improvisation and modification of the mix wind turbine will certainly improve its further performance and efficiency.

In this study, performance of different wind turbines is compared with using QBlade software. Normally wind turbines are categorized as Horizontal Axis Wind Turbine (HAWT) and Vertical axis wind turbine (VAWT) which in this paper Darrieus type as a VAWT is discussed with HAWT. The airfoil selected for this study is NACA 0012 and from simulations it can be resulted how adding blades influence efficiency in wind turbines. In terms of using wind turbines, number of blades is one of the important parameters. QBlade contains the XFOIL airfoil analysis functionalities which makes a software a single tool that comprises all functionality needed for the design and simulation of vertical and horizontal axis wind turbines. The benefits of the proper airfoil design optimal is increasing the efficiency of wind turbines and maximization of the power produced.

Considerable improvements in the aerodynamic performance of a vertical axis wind turbine (VAWT) can be achieved by integrating computational fluid dynamics (CFD) simulation and wind tunnel investigation in their design improvement. With the growing demand for energy worldwide, conventional sources are becoming more scarce and expensive. Wind is among the most popular and fastest growing sources of alternative energy in the world. It is an inexhaustible, indigenous resource, pollution-free, and available almost any time of the day, especially in coastal regions. Industry experts predict that, with proper development, wind energy could provide 20% of the nation’s energy needs. Vertical axis wind turbines (VAWTs) may be as efficient and practical as, and simpler, and significantly cheaper to build and maintain than, horizontal axis wind turbines (HAWTs). They have other inherent advantages; for example, they always face the wind. VAWTs include both a drag-type configuration, such as the Savonius rotor, and a lift-type configuration, such as the Darrieus rotor. The Savonius wind turbine is the simplest. Its operation depends on the difference in drag force when the wind strikes either the convex or concave part of its semi-cylindrical blades. It is good at self-starting and works independently of wind direction. However, its efficiency is relatively lower than that of the lift-type VAWTs. Due to its simple design and low construction cost, Savonius rotors are primarily used for water pumping and to generate wind power on a small scale and its large starting torque makes it suitable for starting other types of wind turbines that have inferior starting characteristics. Recently, some generators with high torque at low rotational speed, suitable for small-scale wind turbines, have been developed, suggesting that Savonius rotors may yet be used to generate electric power. The main goal of this research work is to improve the aerodynamic performance of the three bladed vertical axis Savonius wind turbine. Based on this goal, the objective of this project is to study the performance characteristics of the Savonius wind turbine scale models both experimentally and numerically. The turbine scale models will have different designs with different overlap ratios (ratio of gap between two adjacent blades and the rotor diameter) and without overlap within three blades. The experimental measurements and testing will be conducted in front of a low speed subsonic wind tunnel at different Reynolds number and the computational fluid dynamic (CFD) flow simulation around those design models will be performed by commercial CFD software FLUENT and GAMBIT.

The vertical axis wind turbine (VAWT) is considered an important device to utilize the renewable and sustainable wind energy. However, the relatively lower power coefficient has hampered its development. Therefore, this paper attempts to investigate the effect of swept blade employed in a VAWT on the enhancement in aerodynamic performance. A series of swept blades were studied in a small VAWT rotor, and the RANS SST k-ω turbulence model was utilized to simulate the flow field. The numerical model was validated against experimental data, and the aerodynamic performance was investigated with respect to force coefficients, vorticity distribution, static pressure distribution, and wind turbine wake, respectively. The results indicated that the swept blade could effectively increase power outputs by about 20% for the wind turbine. By reducing the drag coefficient, a high lift-drag ratio was achieved. And this configuration prevented the blade from suffering severe dynamic stall. Besides, the swept blade changed the distribution of low wind speed area in the wind turbine wake, which should be considered in the wind farm. It was concluded that this work provided a new way for the practical design and optimization of wind turbine.

Low order models based on the Blade Element Momentum (BEM) theory exhibit modeling issues in the performance prediction of Vertical Axis Wind Turbines (VAWT) compared to Computational Fluid Dynamics, despite the widespread engineering practice of such methods. The present study shows that the capability of BEM codes applied to VAWTs can be greatly improved by implementing a novel three-dimensional set of high-order corrections and demonstrates this by comparing the BEM predictions against wind-tunnel experiments conducted on three small-scale VAWT models featuring different rotor design (H-shaped and Troposkein), blade profile (NACA0021 and DU-06-W200), and Reynolds number (from 0.8×105 to 2.5×105). Though based on the conventional Double Multiple Stream Tube (DMST) model, the here-presented in-house BEM code incorporates several two-dimensional and three-dimensional corrections including: accurate extended polar data, flow curvature, dynamic stall, a spanwise-distributed formulation of the tip losses, a fully 3D approach in the modeling of rotors featuring general shape (such as but not only, the Troposkein one), and accounting for the passive effects of supporting struts and pole. The detailed comparison with experimental data of the same models, tested in the large-scale wind tunnel of the Politecnico di Milano, suggests the very good predictive capability of the code in terms of power exchange, torque coefficient, and loads, on both time-mean and time-resolved basis. The peculiar formulation of the code allows including in a straightforward way the usual spanwise non-uniformity of the incoming wind and the effects of skew, thus allowing predicting the turbine operation in a realistic open-field in presence of the environmental boundary layer. A systematic study on the operation of VAWTs in multiple environments, such as in coastal regions or off-shore, and highlighting the sensitivity of VAWT performance to blade profile selection, rotor shape and size, wind shear, and rotor tilt concludes the paper.

Double-blade vertical axis wind turbines (DB-VAWTs) can improve the self-starting performance of lift-driven VAWTs. We here propose the quadruple-multiple streamtube model (QMS), based on the blade element momentum (BEM) theory, for simulating DB-VAWT performance. Model validity is investigated by comparison to computational fluid dynamics (CFD) prediction for two kinds of two-dimensional DB-VAWT rotors for two rotor scales with three inner-outer radius ratios: 0.25, 0.5, and 0.75. The BEM-QMS model does not consider the effects of an inner rotor on the flow speed in the upwind half of the rotor, so we introduce a correction factor for this flow speed. The maximum power coefficient predicted by the modified BEM-QMS model for a DB-VAWT is thus closer to the CFD prediction.

Introduction. Nowadays the sector of high-rise and super high-rise buildings construction is rapidly developing. The deficiency of non-renewable energy sources and the deterioration of the environment are two major problems faced by every country. Therefore, the wind power engineering is intensely developing and is able not only to stop the rapid deterioration of environmental situation but also to improve accessibility of energy supply and considerably reduce the deficit of energy. It is rational to use the wind power to source the clean renewable energy for the high-rise buildings by installing the vertical axis wind turbines on the upper floors of the buildings. The aim of the work is to confirm that the vertical axis wind turbines are the best appropriate for installation on the upper floors of high-rise buildings in the cities due to unique advantages thereof (simple design, easy maintenance, adaptability to complicated and changeable wind environment, long operation life), which ensure the supply of the cities with the safe and clean green energy.Materials and Methods. A small-size vertical axis wind turbine was taken for the study. The operation efficiency of various wind turbines was measured by changing the wind strength and direction under the same environmental conditions to determine whether a vertical axis wind turbine could operate safely, sustainably and efficiently in the complicated and changing wind environment of the city. Alongside it was proved that for ensuring the supply of the cities with the safe and clean energy the installation of the vertical axis wind turbines on the upper floors of high-rise buildings is more appropriate compared to the installation of horizontal ones.Results. By changing the wind strength and direction, it was found that the vertical axis wind turbines have good and stable operation efficiency and can provide a constant source of clean energy for urban development in a safer and more stable way.Discussion and Conclusions. The vertical axis wind turbines are ideally adapted to the complicated and changing wind conditions of the upper floors of high-rise buildings and can be safely and efficiently operated, making positive contribution to reducing the energy load and improving the state of environment.

In this paper, the reason was analyzed that the aerodynamic efficiency of the traditional vertical axis wind turbine (VAWT) was always low, and a new type of VAWT—Guiding VAWT was introduced. On that basis, a new blade shape called as combined blade for Guiding VAWT was proposed and numerical investigation was complemented on its aerodynamic performance by CFD (Computational Fluid Dynamics) technique. This Guiding VAWT includes two components: guiding impeller and rotating impeller, which are both combined blade in shape. The guiding blade is combined by three sections: inlet radial section, middle arc section and outlet linear section. The wind blade is combined by two sections, inlet arc section and outlet linear section. The combined guiding blade may not only avoid the wind impeller from the direct impact by the coming flow on its convex surface of the blade so as to decrease the drag torque but also improve the effective impact by the coming flow on the concave surface of the blade, both of which contribute the enhancement for the driving torque of the wind turbine. Results indicate: This new type of Guiding VAWT with combined blade has a wider operating range, higher aerodynamic efficiency than the traditional VAWTs. And more, this paper introduced the airfoil blade into this new type of VAWT and numerically validated that even though the flow inside VAWT was a large separated flow with variable attack angles, the aerodynamic advantage of the airfoil blade could still be shown to some extent, which hoped to further enhance the aerodynamic efficiency of the VAWT. Additionally, this new type of VAWT has a two dimensional structure for convenient manufacture, which has the latent energy to be popularized.

Wind energy, being renewable, cost-effective, and environmentally friendly, has attracted global attention. However, due to suboptimal performance and limited research, vertical axis wind turbines (VAWTs) lag behind horizontal axis wind turbines (HAWTs) in commercial applications, particularly for large-scale installations. This study aims to improve the self-starting capability of the Darrieus VAWT. While some parameters, such as the number of blades (N) and solidity (σ), have been studied extensively, the airfoil shape has not received as much attention. This study compares the performance of National Advisory Committee for Aeronautics (NACA) airfoils and Selig airfoils at a Reynolds number (Re) of 40,673. The investigation revealed that the NACA0015 airfoil exhibited the highest peak power coefficient (Cp). Further analysis utilizing an advanced double multiple stream tube (DMST) code in MATLAB increased the peak Cp by adjusting the thickness-to-camber ratio (t/c) of the NACA0015 airfoil, resulting in a 12.50 % increase in the maximum achievable Cpat a Re of 40,673. This study compared four modes of VAWT operation, utilizing the NACA0015 airfoil and a modified NACA0015 airfoil for both straight-bladed and embossed-bladed VAWTs. The results showed that the modified NACA0015 airfoil for embossed-bladed VAWTs exhibited the best self-starting capability and rotation at wind velocities of 1 to 9 m s-1. Additionally, the self-starting force required by embossed-bladed VAWTs was lower than that needed by straight-bladed VAWTs due to the ability of the embossed material to enhance airflow attachment to the VAWT and suppress turbulence.

Experimental investigation of solidity and other characteristics on dual vertical axis wind turbines in an urban environment

In South East Asia countries such Malaysia, wind turbine is generally not suitable to be used in large scale to generate electricity due to inconsistent wind speed and suitable land site availability. However, a small scale application is of preference as the wind speed in the region lies within the low speed range of approximately 2-5 ms−1 with intermittent highs up to 8 ms−1. The performance of Vertical Axis Wind Turbines (VAWTs) is known to be better compared to Horizontal Axis Wind Turbines (HAWTs) in urban conditions due to its omnidirectionality, which allows it to operate in fluctuating turbulent wind conditions. However, the major drawback of VAWTs is the inability to self-start under low wind speed conditions. Hence, the objective of this work is to investigate the Pivoting Panel Mechanism (PPM) which aims to assist VAWT models to self-start at low wind speed condition. Three sets of PPM width configurations (70mm, 80mm, 90mm) are used to study the effect of increasing the pivot panel surface area on the VAWT performance. Performance test showed that the PPM model improved the power coefficient values at the tip wind speed range of TSR<0.75 (PPM 70mm>80mm>90mm). Further investigation revealed that the larger PPM surface area (90mm) was able to assist the VAWT model to achieve a shorter RPM response time at wind speed of v = 2.5ms−1 and 2.9ms−1. These findings have considerable implications for future researches for the optimization of PPM design parameters and its adaptations in VAWT turbine design.