Lift-type Vertical Axis Wind Turbine Research Articles

Drag reduction of lift-type Vertical axis wind turbine with slit modified Gurney flap

This study examines aerodynamic performance enhancement of Vertical Axis Wind Turbine (VAWT) blades with Gurney flap (GF) modified by slits. A quasi-3D computational fluid dynamics solution based on Reynolds-averaged Navier-Stokes model is employed to evaluate the effectiveness of slit GF blades, in particular the lift-to-drag ratio. The computational domain includes three pairs of GFs and slits combination along the blade span-wise direction to allow quasi-3D flow development while applying translational periodic boundary condition on the two end-wall boundaries. The inlet velocity is 9 m/s for a VAWT configuration with Tip Speed Ratios (TSRs) of 1.44, 2.64, and 3.3, respectively and each of these TSRs represents low, medium, and high regimes of TSRs. Simulation results have shown a significant 8% drag reduction for blades with slit GFs at medium range of TSRs, albeit with a 2% decrease in lift compared to blades with clean GFs. This improves the lift-to-drag ratio and enhances moment production. The power generation also shows increases of 1.5%, 6.5%, and 11.3% at low, medium, and high TSR regimes, respectively, for the analysed slit GF blades. The drag reduction is primarily attributed to the generation of small-scale vortices by the slit, dissipating large coherent flow structures more rapidly in the near wake-field.

Overall aerodynamic performance of the airfoils with different amplitudes via a fuzzy decision making based Taguchi methodology

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.

Numerical Study of Aerodynamic Performance of Airfoil with Variable Curvature Split Flap

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.

Investigation into the Aerodynamic Performance of a Vertical Axis Wind Turbine with Endplate Design

For the past decade, research on vertical axis wind turbines (VAWTs) has garnered immense interest due to their omnidirectional characteristic, especially the lift-type VAWT. The H-rotor Darrieus VAWT operates based on the lift generated by aerofoil blades and typically possesses higher efficiency than the drag-type Savonius VAWT. However, the open-ended blades generate tip loss effects that reduce the power output. Wingtip devices such as winglets and endplates are commonly used in aerofoil design to increase performance by reducing tip losses. In this study, a CFD simulation is conducted using the sliding mesh method and the k-ω SST turbulence model on a two-bladed NACA0018 VAWT. The aerodynamic performance of a VAWT with offset, symmetric V, asymmetric and triangular endplates are presented and compared against the baseline turbine. The simulation was first validated with the wind tunnel experimental data published in the literature. The simulation showed that the endplates reduced the swirling vortex and improved the pressure distribution along the blade span, especially at the blade tip. The relationship between TSR regimes and the tip loss effect is also reported in the paper. Increasing VAWT performance by using endplates to minimise tip loss is a simple yet effective solution. However, the improvement of the power coefficient is not remarkable as the power degradation only involves a small section of the blades.

A review on the use of passive flow control devices as performance enhancement of lift‐type vertical axis wind turbines

AbstractThis article provides a comprehensive review about passive flow control devices (PFCDs) implemented in lift‐type vertical axis wind turbine (LVAWT), focusing on the underlying flow physics mechanisms and to what extents they can improve the LVAWT performance. In addition, some novel concepts that can be potentially implemented in future are also presented. Based on literature review, it is observed that PFCDs can enhance the power generation of LVAWT up to 172.73% compared with a clean LVAWT. However, this significant improvement still needs to be evaluated carefully by considering the economic feasibility aspect, because PCFDs can increase the design complexity, weight penalty and manufacturing cost of LVAWT. Furthermore, it is essential to design and evaluate the effectiveness of PFCDs using a full VAWT configuration by considering the blade rotating effects and blade‐to‐blade interactions. Finally, evaluation of PFCDs needs to be performed at all ranges of tip speed ratios (TSRs) operation conditions, as there are clear evidences on the correlation between LVAWT performance and different range of TSRs.This article is categorized under: Sustainable Energy > Wind Energy

Numerical Simulation and Wind Tunnel Investigation on Static Characteristics of VAWT Rotor Starter with Lift-Drag Combined Structure

In order to get rid of the impact of the global financial crisis and actively respond to global climate change, it has become a common choice for global economic development to develop clean energy such as wind energy, improve energy efficiency and reduce greenhouse gas emissions. With the advantages of simple structure, unnecessary facing the wind direction, and unique appearance, the vertical axis wind turbine (VAWT) attracts extensive attention in the field of small and medium wind turbines. The lift-type VAWT exhibits outstanding aerodynamic characteristics at a high tip speed ratio, while the starting characteristics are generally undesirable at a low wind speed; thus, how to improve the starting characteristics of the lift-type VAWT has always been an important issue. In this paper, a lift-drag combined starter (LDCS) suitable for lift-type VAWT was proposed to optimize the starting characteristics of lift-type VAWT. With semi-elliptical drag blades and lift blades equipped on the middle and rear part outside the starter, the structure is characterized by lift-drag combination, weakening the adverse effect of the starter with semi-elliptical drag blades alone on the output performance of the original lift-type VAWT and improving the characteristics of the lift-drag combined VAWT. The static characteristic is one of the important starting characteristics of the wind turbine. The rapid development of computational fluid dynamics has laid a solid material foundation for VAWT. Thus the static characteristics of the LDCS with different numbers of blades were investigated by conducting numerical simulation and wind tunnel tests. The results demonstrated that the static torque coefficient of LDCS increased significantly with the increased incoming wind speed. The average value of the static torque coefficient also increased significantly. This study can provide guidelines for the research of lift-drag combined wind turbines.

A Study on Relationship among Blade Camber Direction and Pitch Angle and Performance of a Small Straight-Blade Darrieus Wind Turbine by Using Scale Test Model and Gurney Flap

Straight-blade Darrieus vertical axis wind turbines are used as medium and small size wind turbine because of higher power output in vertical axis wind turbine (VAWT). In our previous study, the relationship between the performance and Reynolds number based on airfoil chord length had been investigated by using small-scale test models of lift-type VAWT, and the results showed that the performance of tested wind turbine models with small diameter was clearly lower than that of the large-scale field test machine, and its performance also varies significantly with the blade pitch angle. In this study, we focused on the performance of a small-scale straight-blade Darrieus VAWT, the relationship among the blade airfoil camber direction and the pitch angle, and the performance of the small-scale VAWT was examined experimentally by using a small-scale VAWT test model with Gurney flap which was a small flat plate. Gurney flaps with its height h, as a ratio to the blade chord length c, h/c = 0.036 to 0.055, were attached to the blades of the VAWT test model, in addition, the attaching direction of the Gurney flap on the blade was examined for both inward and outward of the rotor, and the pitch angle was also examined for a range of −5 to 10 degrees. These results are discussed comparing with the result of the VAWT without Gurney flap and considering the numerical results for the single blade with/without the Gurney flap. The results showed that the performance of the tested VAWT was reversed between the inward and outward Gurney flaps around a pitch angle of 10 degrees. That is, the inward Gurney flap was superior at a pitch angle of less than 10 degrees, while the outward Gurney flap was effective at a pitch angle of more than 10 degrees. Furthermore, for the tested small-scale VAWT model, the optimum pitch angle was about 5 degrees, and the inward and shorter Gurney flap showed higher power performance of the VAWT under this pitch angle condition.

A Note on the Decomposition of Aerodynamic Forces Induced by A Wind Turbine Flaps

ABSTRACTIn this study, the aerodynamic characteristics of a vertical-axis wind turbine blade coupled with a high-lift device, such as the Gurney flap at the trailing edge, are investigated. For numerical analysis, the force element theory is used to understand how the Gurney flap influences the force evolution of the lift-type vertical-axis wind turbine. This study shows that the lift and drag can be respectively approximated into four elements, which are induced by volume vorticity, rotational velocity, angular acceleration and surface friction of the flow around the blades. Based on the perspective of the force element theory, the present simulation provides a clear picture of how the Gurney flap influences the formation of the aerodynamic force elements during a rotational cycle for a vertical-axis wind turbine. Simulation results show that the contributions mainly result from the surface vorticities, the rotational acceleration of the airfoil, and the acceleration of the surface.

A review on the historical development of the lift-type vertical axis wind turbine: From onshore to offshore floating application

This paper discusses the historical evolution of the lift-type vertical axis wind turbine (VAWT) since its inception in the early 1930s. The VAWT received almost no development until the early 1970s when engineers in Canada and the USA began to study the VAWT design as a source of generating electricity. Many curved-bladed VAWTs were tested and are reviewed in this paper. Separately, the straight-bladed VAWT was developed by researchers in the UK and is also discussed. This review highlights that the VAWT received very little engineering development in the 1990s due to dominance of the HAWT in the wind energy market. Although, the literature also indicates that the VAWT has entered a Renaissance period whereby the VAWT is now being adopted for the offshore floating wind turbine industry. The latest developments in the floating VAWT technology and attempts to commercialise this technology have been documented.

A study on aerodynamic characteristics and visualization of flow field of lift-drag combined starter

This study refers to the modification of the aerodynamic characteristics of the starter for the lift-type vertical axis wind turbine, the structure of the traditional drag starter was improved, and the lift-drag combined starter model was proposed. Based on the CFD numerical simulation and the particle image velocimetry visualization test, the aerodynamic characteristics of the lift-drag combined starter model and the drag starter model are studied, and the reasons for the regular variation of the flow field are explained. The results show that the lift-drag combined starter has obvious advantages over the traditional drag starter in both static start-up characteristics and dynamic output characteristics. The average static torque coefficient of the lift-drag combined starter is increased by 8% compared to that of the drag starter after one revolution. The increasing percentage of the maximum dynamic moment coefficient of the lift-drag combined starter is 89% compared to the drag starter, and the decreasi...

Optimization Research on Lift-Type Vertical Axis Wind Turbine Airfoil by CFD

The blade airfoil has an important effect on the performance of a lift-type vertical axis wind turbine (VAWT). In this paper, a research has been carried out based on CFD numerical technology to compare the effects of 4 kinds of S series airfoil (S1012, S1016, S1046, S1048) and traditional airfoil NACA0015 on lift-type VAWT. The turbulence model is used k-ω SST model. The simulation results indicate that: The airfoil NACA0015 has the highest torque coefficient and power coefficient. In terms of S series airfoils, the airfoil S1012 has the best performance and airfoil S1016 performs worst. The airfoil S1016 has the largest static torque coefficient. And the airfoil which has higher power coefficient would have a lower static torque coefficient for S series airfoil. The static torque coefficient of airfoil NACA0015 is lower than airfoil S1016 and S1046.

The influence of the number of rotor blades on the performance of orthopter wind turbine

This paper describes the influence of the number of rotor blades the performance of the orthopter wind turbine. The orthopter wind turbine is combination between a drag-type and a lift-type vertical axis wind turbine which each blade combines a rotating movement around its own axis and a rotating movement around turbine's axis. In this case, the pitch of the blades was controlled by using a chain and sprockets arrangement to ensure that the blades rotated around their own axis by 360 degrees during the each two full revolution of the main rotor. To improve the performance of this wind turbine, the number of blades, was investigated by wind tunnel. By conducting two-dimensional unsteady CFD simulations, the power and torque of the vertical axis wind turbine and the flow around blades were also analyzed. The numerical simulation by using turbulence model predicted good agreement of the performance with experiment qualitatively.

Aerodynamic stability of airfoils in lift-type vertical axis wind turbine in steady solver

This paper presents a method examining static forces and moment of airfoil in steady solver. Aerodynamic stability is one subject that many scholars have begun to realize very crucial for design and daily operation. Fundamentals of aerodynamics were firstly scrutinized concerned about lift, drag and moment. Then steady simulation solver is set up instead of transient solver because we would like to examine airfoil without the effect of vortex motion, temporarily focus on static forces on airfoil. Dependent variable include cl, cd and cm of three airfoils, FLAT PLATE, NACA0012 and NACA23012 at TSR = 0, 2, 5 and 7. Stability is characterized by deviation and fluctuation at 360 degrees of azimuth position. We found that FLAT PLATE showed most deviation and fluctuation as an example of airfoil for VAWT. NACA0012 representing symmetric airfoil has more stable cm at whole time and cd just at TSR of 2 and 5. NACA23012 representing cambered airfoil has more stable cl all phases of running.

A detailed investigation of a novel vertical axis Darrieus wind rotor with two sets of blades

The lift-type vertical axis wind turbine (Darrieus rotor) is considered to be a promising device for harnessing wind energy due to its potential advantages. Traditionally, a standard Darrieus rotor has a single ring of airfoils (two or three airfoils) that spins about a vertical axis and has low starting torque. A few researchers have stated that the Darrieus rotor with two sets of blades is likely to improve not only the starting ability but also the power coefficient. However, they have not provided sufficient evidence to support their statement. Thus, in this paper, we conducted a detailed computational fluid dynamics (CFD) investigation on the characteristics (e.g., power output, static torque, vortex, and pressure contours) of this rotor with two sets of blades. The effect of the distance between the outer and inner blades on the performance of this rotor was also discussed and quantified. The findings of this paper are expected to help in developing this new type of Darrieus rotor and offer valuable suggestions for real field applications.

Research on the aerodynamic characteristics of a lift drag hybrid vertical axis wind turbine

Compared with a drag-type vertical axis wind turbines, one of the greatest advantages for a lift-type vertical axis wind turbines is its higher power coefficient ( Cp). However, the lift-type vertical axis wind turbines is not a self-starting turbine as its starting torque is very low. In order to combine the advantage of both the drag-type and the lift-type vertical axis wind turbines, a lift drag hybrid vertical axis wind turbines was designed in this article and its aerodynamics and starting performance was studied in detail with the aid of computational fluid dynamics simulations. Numerical results indicate that the power coefficient of this lift drag hybrid vertical axis wind turbines declines when the distance between its drag-type blades and the center of rotation of the turbine rotor increases, whereas its starting torque can be significantly improved. Studies also show that unlike the lift-type vertical axis wind turbines, this lift drag hybrid-type vertical axis wind turbines could be able to solve the problem of low start-up torque. However, the installation position of the drag blade is very important. If the drag blade is mounted very close to the spindle, the starting torque of the lift drag hybrid-type vertical axis wind turbines may not be improved at all. In addition, it has been found that the power coefficient of the studied vertical axis wind turbines is not as good as expected and possible reasons have been provided in this article after the pressure distribution along the surfaces of the airfoil-shaped blades of the hybrid turbine was analyzed.

Numerical Simulation of Vertical Axis Wind Turbine Blade Airfoil Performance

Research of blade airfoil aerodynamic characteristics is an important foundation for the vertical axis wind turbine aerodynamic design and performance analysis. CFD simulation software has been applied in this paper. Representative lift-type vertical axis wind turbine airfoil NACA0014, NACA2414, NACA4414, NACA6414, NACA8414 's aerodynamic simulation have been studied. Camber airfoil relative with the change in to the flow velocity is analyzed. At different angles of attack effect on the aerodynamic performance of wind turbines, variation of parameters for airfoil aerodynamic had been analyzed. It will help the optimal design of airfoils for vertical axis wind turbines.

Design and Analysis of Small-Scale Lift-Type Vertical-Axis Wind Turbine Using Composite Blade

This paper focuses on verifying the feasibility of applying fibre reinforced polymer matrix composite to vertical axis wind turbine. A small-scale lift-type vertical axis wind turbine using glass fibre reinforced epoxy matrix sandwich composite blade was proposed. An airfoil profile of blade was designed and a composite blade was fabricated. The structure parameters of the blade were optimized by means of the finite element modeling method. The mechanical and the resonant properties of the blade were investigated. Finally, a wind turbine with the designed blade was assembled, and its generating capacity was tested. It was demonstrated that the designed composite blade and the wind turbine had excellent performance, indicating a promising technology for utilizing wind power.

The design, simulation and testing of an urban vertical axis wind turbine with the omni-direction-guide-vane

A novel omni-direction-guide-vane (ODGV) that surrounds a vertical axis wind turbine (VAWT) is designed to improve the wind turbine performance. Wind tunnel testing was performed to evaluate the performance of a 5-bladed (Wortmann FX63-137 airfoil) H-rotor wind turbine, with and without the integration of the ODGV. The test was conducted using a scaled model turbine which was constructed to simulate the VAWT enclosed by the ODGV placed on a building. The VAWT shows an improvement on its self-starting behavior where the cut-in speed was reduced with the integration of the ODGV. Since the VAWT is able to self-start at a lower wind speed, the working hour of the wind turbine would increase. At a wind speed of 6m/s and under free-running condition (only rotor inertia and bearing friction were applied), the ODGV helps to increase the rotor rotational speed by 182%. With extra load application at the same wind speed (6m/s), the wind turbine power output was increased by 3.48 times at its peak torque with the aid of the ODGV. The working concept of the ODGV is to minimize the negative torque zone of a lift-type VAWT and to reduce turbulence and rotational speed fluctuation. It was verified by re-simulating the torque coefficient data of a single bladed (NACA 0015 airfoil) VAWT published by the Sandia National Laboratories. From the simulation results, with the presence of the ODGV, it was shown that the torque output of the NACA 0015 airfoil, single bladed VAWT has been increased by 58% and 39% at TSR=2.5 and TSR=5.1 respectively. The negative torque zone has been minimized thus the positive torque that provides higher power can be obtained. As a conclusion, the ODGV integrated wind power generation system improves the power output of a VAWT and it has great potential to be sited in urban areas for on-site and grid-connected power generation.

Influence of Reynolds Number and Scale on Performance Evaluation of Lift-type Vertical Axis Wind Turbine by Scale-model Wind Tunnel Tests

Abstract For Lift-type Vertical Axis Wind Turbine (VAWT), it is difficult to evaluate the performance through the scale-model wind tunnel tests, because of the scale effect relating to Reynolds number. However, it is beneficial to figure out the critical value of Reynolds number or minimum size of the Lift-type VAWT, when designing this type of micro wind turbine. Therefore, in this study, the performance of several scale-models of Lift-type VAWT (Reynolds number : 1.5x10 4 to 4.6x10 4 ) was investigated. As a result, the Reynolds number effect depends on the blade chord rather than the inlet velocity. In addition, there was a transition point of the Reynolds number to change the dominant driving force from Drag to Lift. Keywords : Vertical Axis Wind Turbine, Wind tunnel, Reynolds number, Performance, Scale effect. 1. Introduction and background Lift-type Vertical Axis Wind Turbine (VAWT) has difficulty of performance evaluation with scale-model wind tunnel tests, because of the scale effect depending on Reynolds number, and there is cost problem in field test with actual size Lift-type VAWT to evaluate several blade shapes or the size and setting angle of blade for performance improvement. If possible, it is useful to evaluate the performance of Lift-type VAWT with scale-model wind tunnel tests and these results can help us to investigate the possibility of Lift-type VAWT as micro wind turbine. However there were few reports [1][2][3] for the performance evaluation of Lift-type VAWT with scale-model wind tunnel tests and almost only the data of field test for actual size Lift-type VAWT [4] that is same type we are investigating in field test [5] were reported. For the reasons mentioned in the above, in this study, several scale-models of Lift-type VAWT were investigated for the performance with changing the pitch angle, blade chord length and blade shape as the experimental parameter of Lift-type VAWT. In performance test, low speed wind tunnel of blow down type was used and the diameter of scale-model of Lift-type VAWT was 1/7 to 1/10 compared with the one for field test [5] mentioned before. The data acquired from the performance tests were evaluated with Reynolds number (

Influence of Reynolds Number and Scale on Performance Evaluation of Lift-type Vertical Axis Wind Turbine by Scale-model Wind Tunnel Tests

Influence of Reynolds Number and Scale on Performance Evaluation of Lift-type Vertical Axis Wind Turbine by Scale-model Wind Tunnel Tests