Straight-bladed Vertical Axis Wind Turbine Research Articles

Numerical and experimental investigation of Darrieus vertical axis wind turbines to enhance self-starting at low wind speeds

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.

Large-eddy simulations of turbulent wake flows behind helical- and straight-bladed vertical axis wind turbines rotating at low tip speed ratios

Large-eddy simulations of turbulent wake flows behind helical- and straight-bladed vertical axis wind turbines rotating at low tip speed ratios

Aerodynamic performance and starting torque enhancement of small-scale Darrieus type straight-bladed vertical axis wind turbines with J-shaped airfoil

Wind energy is one of the most eminent renewable sources for the generation of power. The increasing enthusiasm toward the advancement of small-scale Darrieus type straight-bladed vertical axis wind turbines (SB-VAWTs) can offer a potential remedy for addressing power shortage and the unpredictability of climate conditions. These particular wind turbines provide distinct advantages over their counterparts due to their linear blade design and uncomplicated structure. However, enhancements are required in their aerodynamic efficiency and self-initiation capabilities. These challenges stem from using traditional straight blade configurations and symmetrical airfoils. By substituting these conventional elements with J-shaped straight blades and along with cambered airfoils, these issues can be effectively overcome. The current study aims to investigate the effect of J-shaped straight blades with a series of cambered airfoils to improve the aerodynamic performance and starting torque of small-scale Darrieus type SB-VAWTs. Therefore, experimental and numerical studies are conducted to analyze the J-shaped airfoil impact with various opening ratios systematically. The J-shaped blade profile is designed by eliminating some portion toward the trailing edge of a conventional airfoil. This analysis demonstrated that the J-shaped blade incorporating a cambered NACA 4418 airfoil outperforms its alternative cambered airfoil designs. The performance of SB-VAWT improves by about 25% by the J-shape of the cambered NACA 4418 airfoil with a 70% opening ratio. Moreover, the use of J-shaped airfoils enhances the self-starting torque of SB-VAWT compared to conventional airfoils.

Development and Application of an FSI Model for Floating VAWT by Coupling CFD and FEA

The emerging floating vertical axis wind turbines (VAWTs) are regarded as a preferred solution to overcome the challenges faced by the traditional horizontal type in open-sea environments. Numerous numerical models have been advanced for assessing this novel object. However, current fully coupled models predominantly rely on simplified theories, assuming a linear fluid load and a one-dimensional slender beam structure. Despite computational fluid dynamic and finite element (CFD-FEA) coupling being qualified for high precision, this technology remains limited to the fixed VAWT field. To predict the load and structural response accurately and comprehensively, this study aims to extend CFD-FEA technology to floating VAWTs. First, an aero-hydro-moor-elastic fully coupled model is developed, and this model is validated by comparing it with several model experiments. Subsequently, a full-scale floating straight-bladed VAWT is simulated with the geometry and numerical models introduced. Furthermore, load and structural responses in a typical case are analyzed in both time and frequency domains. Finally, the sensitivity analysis of each structure part in floating VAWTs to environmental parameters is conducted and discussed. The discovery highlights the intricate nature of tower structural response, which incorporates 2-node, 3-node, wind frequency, and wave frequency components. Distinct from blades or floating foundations, which are primarily influenced by a single environmental parameter, the tower response is significantly amplified by the combined effects of wind and waves.

Computational fluid dynamics study on the efficiency of straight-bladed vertical axis wind turbine

The present study treats numerically the performance of a straight-bladed, vertical axis, Darieus wind turbine. A two-dimensional (2D), Unsteady Reynolds-averaged Navier–Stokes (URANS) simulations were performed out by the solver ANSYS/FLUENT using the sliding mesh method. Four turbulence models, namely the one-equation Spalart– Almaras (SA) model, the two-equation Shear Stress Transport (SST) k-ω, the Transitional Shear Stress Transport (TSST), and the realizable k-ϵ models, with low Reynolds number capabilities, were tested.The dependency of the power curve upon the torque coefficient and the Tip Speed Ratio (TSR) was evaluated under identical conditions to previously published experimental studies. The results suggest that the realizable k-ϵ model outperformed other turbulence models and matched better with the experimental data. Further numerical investigations were performed to determine the conditions for an optimal performance of the VAWT in question.

Wind tunnel experimental study on the aerodynamic characteristics of straight-bladed vertical axis wind turbine

ABSTRACT To investigate the effect of structural parameters on the aerodynamic characteristics of a Straight-Bladed Vertical Axis Wind Turbine (SB-VAWT), a 4-bladed SB-VAWT without an intermediate support shaft was designed to allow flexibility in changing structural parameters. Wind tunnel tests were conducted to measure the rotational speed, total lift, drag and torque of the wind turbine with different structural parameters at varying wind speeds. Based on the experimental design and optimisation, the wind turbine achieved the highest rotational speed and optimal power generation when the blades were installed in the forward direction at an installation angle of 10°, an installation radius of 160 mm, and a length of 600 mm. Under these optimal conditions, the speed and power generation characteristics of the wind turbine were tested at different wind speeds These results provide valuable insights for the design and application of similar wind turbines.

Design approach of thrust-matched rotor for basin model tests of floating straight-bladed vertical axis wind turbines

Rotor redesign approaches have been widely proposed to solve the thrust mismatch issue caused by scaling effects for basin model tests of horizontal axis floating wind turbines (FWTs). However, limited basin model tests utilized the thrust-matched rotor (TMR) to accurately evaluate the aerodynamic loads applying to the vertical axis FWTs. This paper described the detailed design approach of the TMR of floating straight-bladed vertical axis wind turbines (VAWTs) with a rated power of 5.3 MW. First, the AG455 airfoil was selected to replace the NACA0018 airfoil. AG455 airfoil can show a larger lift coefficient and a smaller drag coefficient at low Reynolds number. On this basis, the load distribution match algorithm was used to assign the blade pitch angle and chord length at each section of the blade. This method takes the spanwise load and load change rate of model-scaled blade and full-scaled blade as the constraint conditions. By adopting this method, the rotor thrust can be tailored to match the prototype values across a wide range of tip speed ratios. This design approach proves advantageous in assessing the aerodynamic performance of VAWTs under varying inflow wind speeds and unsteady wind conditions. The redesigned TMR model under low Reynolds number can meet Froude similarity criterion, which is helpful to improve the accuracy of vertical axis FWT model tests in the wave basin.

Large-eddy simulations of turbulent flows in arrays of helical- and straight-bladed vertical-axis wind turbines

Effects of helical-shaped blades on the flow characteristics and power production of finite-length wind farms composed of vertical-axis wind turbines (VAWTs) are studied numerically using large-eddy simulation (LES). Two helical-bladed VAWTs (with opposite blade twist angles) are studied against one straight-bladed VAWT in different array configurations with coarse, intermediate, and tight spacings. Statistical analysis of the LES data shows that the helical-bladed VAWTs can improve the mean power production in the fully developed region of the array by about 4.94%–7.33% compared with the corresponding straight-bladed VAWT cases. The helical-bladed VAWTs also cover the azimuth angle more smoothly during the rotation, resulting in about 47.6%–60.1% reduction in the temporal fluctuation of the VAWT power output. Using the helical-bladed VAWTs also reduces the fatigue load on the structure by significantly reducing the spanwise bending moment (relative to the bottom base), which may improve the longevity of the VAWT system to reduce the long-term maintenance cost.

Numerical study on aerodynamic performance improvement of the straight-bladed vertical axis wind turbine by using wind concentrators

The present study proposes a new concept of Straight-bladed Vertical Axis Wind Turbines (SB-VAWTs) with convex-shaped wind concentrator. The wind concentrator is installed up and down the rotor, which is designed to capture more airflow and improve the flow characteristics inside the rotor. The profile of the wind concentrator is generated based on the B-spline, the quadratic rotational orthogonal combination design method is used to study the effects of bottom radius R1, top radius R2, inlet angle α1, and outlet angle α2 of the concentrator, and the distance ΔL between the concentrator and the rotor on the aerodynamic performance of the SB-VAWT by numerical simulation. It is found that the installation of the wind concentrator improves the flow characteristics inside the rotor and enhances the aerodynamic performance of the SB-VAWT, particularly at lower wind speeds. Under the condition of this study, the average torque coefficient and maximum power coefficient of the SB-VAWT with the wind concentrator are enhanced by up to 24.7 % and 52.7 %. This study can provide a reference for using a wind concentrator to improve the aerodynamic characteristics of SB-VAWTs and demonstrate the potential of using this kind of SB-VAWT for wind energy utilization systems.

Wind tunnel experimental study on static aerodynamic performance of SB-VAWT without intermediate support axes

Wind power generation is considered an effective way for ships to harness wind energy, and the aerodynamic characteristics of wind turbines determine wind energy utilization and efficiency. However, traditional vertical axis wind turbines have intermediate shafts and support rods, which result in large negative effects in the research of the wind turbine aerodynamic characteristics. To address this issue, a Straight-Bladed Vertical Axis Wind Turbine (SB-VAWT) without intermediate support axes is proposed. The turbine can flexibly change the number of blades, rotor diameter, and installation position of blades. The static aerodynamic performance of the wind turbine with different combinations was tested in a wind tunnel laboratory at 10 m/s. The results show that the radius of the wind turbine has a greater effect on the drag coefficient for the same number of blades, with an inverse relationship between the drag coefficient and radius, and a positive association between lift coefficient, static torque coefficient, and radius. The drag coefficient is proportional to the number of blades at the same radius, while the static torque coefficient is inversely proportional to the number of blades. According to the results, placing the initial location in the azimuth range between 30° and 50° can obtain the maximum initial starting torque. Moreover, a wind turbine with a radius of 16 cm can achieve a higher average torque. Changes in the number of blades can significantly impact turbine properties, resulting in wind turbines with distinct features.

Effects of blade tip flow on aerodynamic characteristics of straight-bladed vertical axis wind turbines

Straight-bladed vertical axis wind turbines (SB-VAWTs) are increasingly recognized as a favorable choice for wind energy systems in both urban and offshore environments. This study examines the effects of the blade tip flow on the aerodynamic characteristics of SB-VAWTs by numerical simulation. The analysis employs a comprehensive set of 84 models, varying in parameters such as rotor diameters, blade chord lengths, tip speed ratios, blade aspect ratios (ARs), and airfoil types. Initially, the blade is modeled using the finite division method, followed by a comprehensive three-dimensional URANS numerical simulation. A comprehensive analysis of the aerodynamic performance across the blade span is conducted to quantify the effects of the blade tip flow. The findings indicate that, in addition to causing losses, the tip flow also encourages reattachment of the separated flow onto the blade surface, especially under conditions of stronger flow separation. The influence of the tip flow reduces with a higher AR for AR less than 8. However, when AR surpasses 8, the effect of tip flow stabilizes. This study will serve as a valuable reference for the design of SB-VAWTs and lay the groundwork for future research on blade tip optimization.

Power Output Enhancement of Straight-Bladed Vertical-Axis Wind Turbines with Surrounding Structures

Wind tunnel experiments were conducted by installing wind-acceleration structures on both sides of a straight-bladed vertical-axis wind turbine (VAWT) to improve the output performance of the turbine. In the case of Venturi-shape structures, a curved shape with a large outlet opening produced a higher power output than straight or brimmed Venturi shapes. More importantly, two simple flat plates installed upstream of the wind turbine achieved the highest power enhancement of 2.4 times the power of the bare wind turbine. From the analysis of the flow visualization results, the power enhancement was attributed to the increase in lift force on the blades in the upstream region due to the acceleration of the gap flow between the flat plates, and the decrease in drag force on the blades toward the upstream region due to stagnation of the flow behind the plates.

Fundamentals of different wind turbines for electricity generation and their modelling methods using different algorithms

<p><strong><em> </em></strong>Increased concern for the environment has led to the search for more environment-friendly energy sources so that wind energy can be used as an endless option for human consumption. Wind turbines offer a promising solution for off-grid areas. However, they have certain drawbacks associated with different configurations. Darrieus turbine is one type that can be more efficient than other types. The poor start-up performance of Darrieus turbines is one of the critical problems restricting its development. Another problem of this kind of wind turbine is tackled by identifying the optimization parameters, such as complex flow dynamics around the system. The present article reviews modeling vertical axis turbines methods and discusses the turbine’s operation by presenting the results of these methods. In this review, the authors have attempted to compile the main aerodynamic models that have been used for performance prediction and design of straight-bladed Darrieus-type VAWT. The main object of this study is to research the advantages and disadvantages of wind turbine modeling methods, and the selection of these methods depends on the purpose of the modeling.<strong><em></em></strong></p>

Synergistic Effect of J-Shape Airfoil on the Performance of Darrieus-Type Straight-Bladed Vertical Axis Wind Turbine

AbstractDarrieus-type straight-bladed vertical axis wind turbines (SB-VAWTs) are more appropriate for generating electricity than other VAWTs mostly suitable for regions having low to medium wind speed. The installation of SB-VAWTs faces start-up problems, which limits its applicability in low-wind speed environments. The start-up problem arises mainly due to the cross-sectional blade profile of the SB-VAWTs and is the crucial parameter used for blade design. To overcome this issue, the present investigation aims to study the influence of the J-shape airfoil with various opening ratios in the Darrieus-type SB-VAWTs in terms of starting torque and aerodynamic performance. The design of a J-shape airfoil is created by removing a portion toward the trailing edge of the conventional NACA 4415 airfoil on its upper or lower surface. This analysis displays a maximum power coefficient of 0.517, 0.512, 0.506, 0.498, and 0.488 when the Darrieus-type SB-VAWT utilizes upper cut J-shape airfoils with opening ratios of 0.8, 0.7, 0.6, 0.5, and 0.4, respectively, at the tip speed ratio (TSR) of 1.6. These values are higher than the power coefficient (0.486) of conventional NACA 4415 airfoil at the same TSR. The SB-VAWT depicts a lower performance while it employs the lower cut J-shape airfoils. Furthermore, the present study demonstrates that the power and torque coefficient of SB-VAWT improves by about 31% when the opening ratio of upper cut J-shape airfoil is varied from 0.1 to 0.8.

Effects of blade airfoil chord length and rotor diameter on aerodynamic performance of straight-bladed vertical axis wind turbines by numerical simulation

Straight-bladed Vertical Axis Wind Turbines (SB-VAWTs) have recently attracted much attention as they are considered to be an option for wind energy utilization, whether in offshore or urban environments. In this study, the effects of airfoil chord length and rotor diameter (circumference) on the aerodynamic characteristics of SB-VAWTs were explored by numerical simulation. The research object is a three-bladed SB-VAWT fitted with a NACA0018 symmetric airfoil. A dimensionless parameter RCC is proposed, that is, the ratio of the airfoil chord length to the circumference of the rotor. There are 43 different combinations of chord length and rotor diameter designed for the present study, making the RCC ranges between 1.4% and 57.3%. When the length of airfoil chord is constant and the diameter of rotor changes, the recommended RCC is supposed to be approximately 8% for the SB-VAWT. Differently, when the diameter of the rotor is constant and the length of airfoil chord changes, the recommended RCC is supposed to range between 9.5% and 13.4%. Based on the results, it is confirmed that the RCC is a significant parameter for the design of the SB-VAWT. This study is expected to provide a practical reference for the parametric structural design of SB-VAWTs.

Recommendation for strut designs of vertical axis wind turbines: Effects of strut profiles and connecting configurations on the aerodynamic performance

The strut is a necessary support structure that connects the vertical axis wind turbine blade to the rotating shaft and transfers the torque, and is one of the key factors affecting the aerodynamic performance of the wind turbine. However, research on struts is limited and the appropriate strut design remain uncertain. Therefore, in this paper, the struts of a straight-bladed vertical axis wind turbine are investigated by a three-dimensional computational fluid dynamics approach, to find the appropriate strut design parameters that minimize the impact on the aerodynamic performance. Thirty strut profiles with different chord lengths, thicknesses, areas, and streamlined shapes were parametrically created and analyzed, including a novel strut-specific profile proposed in this paper. Furthermore, all strut connecting parameters, such as spanwise and chordwise positions, connecting angle and fairing were investigated. The results show that the power loss of a vertical axis wind turbine has a relatively linear relationship with the dimensionless absolute thickness of the strut within a certain range. The strut chord length is another important influencing factor. Equal chord lengths of the strut and the blade should be avoided as much as possible. The proposed novel olivary strut profile has lower drag characteristics and more favorable geometrical structural properties compared to the most used NACA airfoil. The influence of the spanwise connecting position (within the range around the blade quarter span) is minor. But the chordwise position has a significant effect, and special attention should be paid to avoid the strut maximum thickness position connecting with the blade aerodynamic center, which will result in the greatest performance degradation. Analysis of the connecting angles shows that inclined struts are suitable for small wind turbines. The fairing is effective when the strut chord length is equal to or longer than the blade chord length. With these results, a set of recommended design parameters for vertical axis wind turbine struts is presented.

Effect of blade aspect ratio on the performance of a pair of vertical axis wind turbines

The effect of blade aspect ratio on the power generation of a pair of straight-bladed vertical axis wind turbines was studies using computational fluid dynamics simulations. Sixteen numerical experiments were performed, and coefficients of power of isolated and paired wind turbines were evaluated at four different blade aspect ratios, including 4, 6, 8, and 10 at solidities of 0.25 and 0.45. It was realized that at each solidity, coefficients of power of isolated and paired wind turbines increased by increasing the blade aspect ratio. At the solidity of 0.25, the power improvement of paired wind turbines compared to an isolated wind turbine increased from 2% at the aspect ratio of 4 to 5% at the aspect ratio of 10. While at the solidity of 0.45, the power increment of paired wind turbines compared to an isolated wind turbine was 18.5% at the aspect ratio of 4 and 23.5% at the aspect ratio of 10. Investigating the velocity contour plots revealed that the rate of wake recovery behind wind turbines decreased by increasing the blade aspect ratio.

Large-eddy simulation of helical- and straight-bladed vertical-axis wind turbines in boundary layer turbulence

Turbulent wake flows behind helical- and straight-bladed vertical axis wind turbines (VAWTs) in boundary layer turbulence are numerically studied using the large-eddy simulation (LES) method combined with the actuator line model. Based on the LES data, systematic statistical analyses are performed to explore the effects of blade geometry on the characteristics of the turbine wake. The time-averaged velocity fields show that the helical-bladed VAWT generates a mean vertical velocity along the center of the turbine wake, which causes a vertical inclination of the turbine wake and alters the vertical gradient of the mean streamwise velocity. Consequently, the intensities of the turbulent fluctuations and Reynolds shear stresses are also affected by the helical-shaped blades when compared with those in the straight-bladed VAWT case. The LES results also show that reversing the twist direction of the helical-bladed VAWT causes the spatial patterns of the turbulent wake flow statistics to be reversed in the vertical direction. Moreover, the mass and kinetic energy transports in the turbine wakes are directly visualized using the transport tube method, and the comparison between the helical- and straight-bladed VAWT cases show significant differences in the downstream evolution of the transport tubes.

An application of cantilevered plates subjected to extremely large amplitude deformations: A self-starting mechanism for vertical axis wind turbines

The use of Darrieus straight-bladed vertical axis wind turbines (VAWTs) are becoming increasingly attractive for wind energy harvesting thanks to their distinctive advantages, even though these lift-force driven wind turbines suffer from anaemic self-starting capability, especially in areas with irregular wind regimes. In this paper, a novel self-starting mechanism is proposed for VAWTs. The proposed concept centres on the use of pliable plates in either of two distinct configurations: (i) with plates attached to the trailing edge of the rigid airfoil-shape blades of the VAWT; (ii) with plates installed inside the VAWT at a distance from the rotor. The feasibility of these designs for self-starting has been investigated theoretically. In particular, flexible blades are idealized as cantilevered beams placed at an angle to a uniform steady flow. Using a Hamiltonian framework, a geometrically-exact fluid-elastic continuum model is developed for the extremely large-amplitude deflections of the flexible blades. The fidelity of the developed framework is first validated against two sets of experimental data available in the literature. The developed framework is then used to estimate the static torque coefficients generated by the flexible plates in both aforementioned VAWT configurations. Finally, the self-starting efficacy of the proposed design is compared against a Savonius based mechanism used in a well-studied benchmark Darrieus–Savonius turbine. The numerical simulations reveal that, regardless of the initial static positions of the turbine, proper engineering of the pliable plates results in a torque generation capability which spins the turbine, even at low wind speeds. This finding proves the feasibility of the proposed concept as a potential self-starting mechanism for VAWTs. The advantages of this mechanism, such as easier design, manufacturing and implementation, enhanced reliability and economical maintenance, make this concept worthwhile for further exploration.

Effect of the bionic blade on the flow field of a straight-bladed vertical axis wind turbine

This paper uses the Particle Image Velocimetry technique through wind tunnel experiments to investigate the spanwise velocity and vortex characteristics of a straight-bladed vertical axis wind turbine (VAWT) and to verify the reliability of the numerical simulation model. The aerodynamic forces are obtained by a multiport pressure measurement device. To assess the flow field of VAWT with bionic blades, this paper compares results between numerical simulations and experiments. Different flow field characteristics of wind turbines have been found in the baseline blades and bionic blades. The research shows that the bionic blade can suppress the influence of the tip vortex on the velocity of the cross-section z/(H/2) = 1.0, and the wake recovery velocity of VAWT with bionic blades is lower than that with baseline blades. By comparing the tangential force coefficients of the blades, it has been found that the tangential force of the bionic blades increases in azimuth angle regions 30°<θ < 116° and 193°<θ < 301°. It has also been proven that the aerodynamic performance of the bionic blade is slightly better than the baseline blades at TSR = 2.19. This study provides a better understanding of the development of aerodynamic forces and vortex characteristics through torque and velocity measurements.