Straight-bladed Vertical Axis Wind Turbine Research Articles

Study on Aerodynamic Performance of a Straight-Bladed VAWT Using a Wind-Gathering Device With Polyline Hexagonal Pyramid Shape

The self-starting performance and aerodynamic characteristics at low wind speeds are the two main problems for the straight-bladed vertical Axis wind turbine (SB-VAWT). In this study, a new kind of wind-gathering device (WGD), which can be installed up and down the rotor, with a polyline hexagonal pyramid shape, was proposed. Both the numerical simulation and the wind tunnel test were performed on this WGD. Based on the method of quadratic rotary orthogonal combination design, the effect of the main structural parameters of the WGD on the self-starting performance of the SB-VAWT was researched by 3D numerical simulation. The optimal combination of the main structural parameters for the WGD under the condition of this study was obtained. Furthermore, wind tunnel tests were carried out on the SB-VAWT with and without the WGD having the optimal structural parameters, including the starting performance, power performance, and rotational revolution performance. The results showed that both the static performance and dynamic performance of the SB-VAWT were increased to some degree by installing this kind of WGD. The improvement is more obvious under the condition of low wind speed. This research can be a useful reference for the in-depth study on the optimal WGDs for the SB-VAWTs.

Transient analysis of H-type Vertical Axis Wind Turbines using CFD

In this study, the effect of various parameters on the start-up and transient behavior of Darrieus straight-bladed Vertical Axis Wind Turbine (VAWT) was analyzed. Airfoil profile, angle-of-attack, and chord length were varied, yielding two optimal turbines, one for transient and another for steady performance. This optimization revealed that the chord length (solidity) has the most significant impact on the performance of the turbine undergoing both transient and steady operations. An examination of the contribution of drag and lift forces to the startup of these two optimized turbines shows that the drag has a positive contribution to the performance of the transient optimized turbine especially at high TSRs. The performance of the optimized turbines when subject to four different wind profiles: a real wind profile, and three distinct sinusoidal profiles was also assessed. At low average wind speeds, a high frequency of the incoming wind is favorable for allowing both optimized turbines to produce more power. The rotor behavior under dynamic loads was also investigated, demonstrating that the transient optimized turbine is more responsive and therefore easier to control. In addition, minimizing the inertia of the steady-optimized turbine significantly improves its startup characteristics, making it superior to its steady-optimized counterpart.

Comparison of Three-Dimensional Numerical Methods for Modeling of Strut Effect on the Performance of a Vertical Axis Wind Turbine

This paper compares three different numerical models to evaluate their accuracy for predicting the performance of an H-rotor vertical-axis wind turbine (VAWT) considering the influence of struts. The strut of VAWTs is one factor that makes the flow feature around the turbine more complex and thus influences the rotor performance. The focus of this study is placed on analyzing how accurately three different numerical approaches are able to reproduce the force distribution and the resulting power, taking the strut effect into account. For the 12 kW straight-bladed VAWT, the blade force is simulated at three tip speed ratios by the full computational fluid dynamics (CFD) model based on the Reynolds-averaged Navier–Stokes (RANS) equations, the actuator line model (ALM), and the vortex model. The results show that all the models do not indicate a significant influence of the struts in the total force over one revolution at low tip speed ratio. However, at middle and high tip speed ratio, the RANS model reproduces the significant decrease of the total tangential force that is caused due to the strut. Additionally, the RANS and vortex models present a clear influence of the struts in the force distribution along the blade at all three tip speed ratios investigated. The prediction by the ALM does not show such distinctive features of the strut impact. The RANS model is superior to the other two models for predicting the power coefficient considering the strut effect, especially at high tip speed ratio.

Optimization analysis of straight-bladed vertical axis wind turbines in turbulent environments by wind tunnel testing

Although freestream turbulence is believed to improve the efficiency of vertical axis wind turbines (VAWTs), few studies have systematically assessed VAWT performance in turbulent environments. In this study, steel and aluminum grids were used to simulate the turbulence field. Three turbulence levels of Iu = 5.1%, 10.9% and 14.6% were generated, together with one low turbulence level of 0.9%. First, the parametric effects of solidity ratio σ, pitch angle β, and aspect ratio η were examined in 48 cases in various flow regimes. Then, the Taguchi method with an L16(44) orthogonal table was implemented to comprehensively and effectively investigate the parametric effects and their extent of impact on VAWT turbine performance. This reduced the number of cases from 256 to 16. Unlike smooth flow, turbulence enhanced the efficiency of the VAWTs, with improvements ranging from 7.9% to 38.0%. The factors influenced efficiency in the following order: β > σ > η > Iu. The VAWT performance peaked at β = −6.5°, and revealed that a toe-out pitch ranging from −9.5° to −6.5° is required for maximal performance. The improvements in VAWT efficiency caused by turbulence decreased as a factor approached its optimal value.

Effects of Blade Numbers on Wind-Induced Fatigue Lives of Straight-Bladed Vertical-Axis Wind-Turbine Tower Bases

Vertical-axis wind turbines (VAWTs) are being reconsidered as a complementary technology to the more commercially used horizontal-axis wind turbines (HAWTs) because of their economical installation and maintenance. The selection of the blade numbers is one of the crucial concerns for VAWTs. This study focuses on the effects of the blade numbers on the fatigue lives of VAWT tower bases subjected to wind loading. Three straight-bladed VAWTs, with the same solidity ratios but different blade numbers, varying from two to four, were designed. The aerodynamic loading incurred by the VAWTs was computed using the corrected double-disk multistreamtube (DMS) model. The dynamic equations of the turbine systems were solved using the explicit central difference method. Then, a fatigue assessment model, including the crack-initiation and crack-propagation stages, was developed for the turbine tower bases. The results indicate that the three- and four-bladed VAWTs always presented better performances than the two-bladed VAWT in terms of the fatigue life. Moreover, increasing the number of blades from two to three improves the fatigue life of the tower base more than increasing it from three to four at lower wind speeds, while the latter is the more effective way to improve the tower-base fatigue life at higher wind speeds.

Experimental study on the wake of straight-bladed vertical axis wind turbine

Experimental study on the wake of straight-bladed vertical axis wind turbine

Aeroelastična analiza lopatice vetroturbine sa ravnim lopaticama vertikalne ose

To prevent flutter phenomena in a wind turbine, minimize vibration and increase the blades' life, a systematic analysis is required to investigate the effects between the cyclic aerodynamic loads and the structural performance of the turbine. A dynamic analysis of a straight-bladed vertical axis wind turbine (SB-VAWT) blade is investigated in this paper, and a simplified approach for the energy equations of an Eulerian beam subjected to twist and transverse bending deflections is introduced. The aerodynamic loads are estimated using the double multiple stream tube models. They are introduced into the dynamic model in the aeroelastic coupling, where the structural displacements are fed back to update the aerodynamic loads by utilizing the average acceleration method for the numerical integration of the equations. Reduced order modeling is then imposed based on the first modes of vibration. It is found that the structural displacement has little effect on the aerodynamic loads, and SBVAWTs experience higher transverse displacements compared with those in curved-blade VAWTs.

Performance assessment of an innovative Gurney flap for straight-bladed vertical axis wind turbine

Based on the vortex trapping capability of the cavity and the lift improvement mechanism for the Gurney Flap (GF), their combined impact on aerodynamic efficiency of the straight-bladed vertical axis wind turbine (SB-VAWT) was investigated. In order to eliminate the flow resistance of the blade caused by GF in the windward zone, an active flow control technique, a pivoting GF could change its position as the blades rotates in a cycle, is proposed in this paper. A grid sensitivity analysis by Grid Convergence Index (GCI) is first carried out to examine the convergence of the numerical model. Considering different GF control strategies, Computational fluid dynamics (CFD) method was used to evaluate the potential of the movable cavity-GF (c-GF) for power augmentation of SB-VAWT with traditional fixed cavity-GF. The simulation results show that power coefficient for movable c-GF is increased by more than 20% in comparison with the clean one. An appropriate active control solution not only has excellent power extraction in the downwind revolution, but also can significantly eliminate the resistance effect in the upwind zone cause by fixed c-GF. In addition, the benefits of the movable c-GF were prominent especially at the smaller tip speed ratios which indicates that it can be used for both newly designed turbines and retrofitting solutions for existing rotors.

Aeroacoustic noise prediction of a vertical axis wind turbine using large eddy simulation

This study investigates the numerical prediction for the aerodynamic noise of the vertical axis wind turbine using large eddy simulation and the acoustic analogy. Low noise designs are required especially in residential areas, and sound level generated by the wind turbine is therefore important to estimate. In this paper, the incompressible flow field around the 12 kW straight-bladed vertical axis wind turbine with the rotor diameter of 6.5 m is solved, and the sound propagation is calculated based on the Ffowcs Williams and Hawkings acoustic analogy. The sound pressure for the turbine operating at high tip speed ratio is predicted, and it is validated by comparing with measurement. The measured spectra of the sound pressure observed at several azimuth angles show the broadband characteristics, and the prediction is able to reproduce the shape of these spectra. While previous works studying small-scaled vertical axis wind turbines found that the thickness noise is the dominant sound source, the loading noise can be considered to be a main contribution to the total sound for this turbine. The simulation also indicates that the received noise level is higher when the blade moves in the downwind than in the upwind side.

Numerical study of aerodynamic characteristics on a straight-bladed vertical axis wind turbine with bionic blades

This paper has attempted to investigate the aerodynamic characteristics of the straight-bladed vertical axis wind turbine (VAWT) with bionic blades for better application of bionic blades to VAWTs. The study was based on the computational fluid dynamics numerical simulation (CFD numerical simulation) technique to investigate the differences of the power and tangential force coefficients of the wind turbine between the bionic blades and standard blades at three different tip speed ratios (TSRs = 1.38, 2.19, and 2.58) for the mainstream wind velocity of 8.0 m/s. The results showed that the average power coefficient enhancing effect of the bionic blade increases as the TSR increases, and the average power coefficient of the bionic blade is higher than that of the standard blade mainly because of the high wind energy utilization in the wave trough section. Moreover, the power coefficients of the wave crest sections for bionic blades are better than that of the standard blades at the downstream region of 200° < θ < 260°. This research provides a reference for the use of bionic blades in the straight-bladed VAWT.

Performance enhancement of straight-bladed vertical axis wind turbines via active flow control strategies: a review

Performance enhancement of straight-bladed vertical axis wind turbines via active flow control strategies: a review

Investigating of Flow Field and Power Performance on a Straight-blade Vertical Axis Wind Turbine with CFD Simulation

Forecasting the power performance and flow field of straight-blade vertical axis wind turbine (VAWT) and paying attention to the dynamic stall can enhance more adaptability to high turbulence and complicated wind conditions in cities environment. According to the blade element-momentum theory, the force of blade is analyzed in one period of revolution based on the structural characteristics of straight blade airfoil. The power performance of VAWT obtained by computational fluid dynamics (CFD) simulation is compared with experiment to estimate the accuracy about the numerical simulation results. As a result, the trend of average value of simulation Cpower is entirely consistent with the value of experiment data, and the extreme value of average Cpower of VAWT is 0.225 for tip speed ration (TSR) λ=2.19 when the freestream velocity is 8 m/s. The flow separation around the blade surface also gradually changes with the azimuth angle increasing, and the maximum pressure difference on the blade surface appears in the upstream. In the case of high leaf tip velocity, the synthetic velocity is much larger than the incoming wind velocity, and the angle of synthetic velocity increases slightly with the increase of blade tangential velocity. Thus, the angles of attack are very close in two TSRs λ=2.19 and 2.58. The research provides a computational model and theoretical basis for predicting wind turbine flow field to improve wind turbine power performance.

Review of Numerical and Experimental Studies on Flow Characteristics around A Straight-bladed Vertical Axis Wind Turbine and Its Performance Enhancement Strategies

Review of Numerical and Experimental Studies on Flow Characteristics around A Straight-bladed Vertical Axis Wind Turbine and Its Performance Enhancement Strategies

Effect of trailing edge dual synthesis jets actuator on aerodynamic characteristics of a straight-bladed vertical axis wind turbine

Based on the improved effect of synthetic jet (SJ) on airfoil aerodynamic characteristics and the configuration characteristics of dual synthesis jets actuator (DSJ), the effects of DSJ actuators arranged at the trailing edge on the aerodynamic efficiency of straight-blade vertical axis wind turbine (SB-VAWT) were studied. By comparing with the experimental results, the accuracy of the numerical simulation results of clean SB-VAWT power coefficient is verified. In order to consider the control effect of the arrangement, the actuation frequency and the momentum coefficient, the Unsteady Reynolds-Averaged Navier-Stokes (URANS) and the SST k-ω turbulence model were used to simulate the SB-VAWT with different types and parameters. The simulation results show that the three arrangement modes of the trailing edge DSJ actuator proposed in this paper can effectively improve the power capacity of VAWT. Among them, Juxtaposition-type is the best. Through periodic “blowing” and “sucking”, the trailing edge vortex is induced to fall off in advance and delay the occurrence of stall. When λ = 2.05, f = 360 Hz, Cμ = 1.975 × 10−2, the power coefficient can be increased by 58.87%.

Wind tunnel tests of the rime icing characteristics of a straight-bladed vertical axis wind turbine

For the wind turbines installed in the cold and humid regions, icing accretion on the blade surface seriously degrades its performance. The Straight-Bladed Vertical Axis Wind Turbine (SB-VAWT) is also troubled by the problem. For exploring the characteristics of icing, the icing wind tunnel tests have been carried out in this paper. An icing wind tunnel experimental system is designed and fabricated. The experimental parameters in the icing wind tunnel system are measured. A rotor test stand with two blades of NACA0018 airfoil is designed and amounted in the icing wind tunnel. The icing test is conducted under the different tip speed ratios and the rime ice condition. The experimental results show that the rotational speed of the blade has significant effects on the characteristics of icing. When the tip speed ratio is lower than 1, the ice layer covers in the whole blade surface and grows layer by layer. As the tip speed ratio is higher than 1, the ice layer mainly concentrates in the vicinity of the leading edge. Three factors, which are the relative angle of attack, the rotational position of blade and the centrifugal force, influencing on the characteristics of icing are analyzed and discussed.

Numerical simulation and experimental study of blade pitch effect on Darrieus straight-bladed wind turbine with high solidity

Increasing the solidity in vertical axis wind turbines (VAWT) leads to the decreased coefficient of performance (COP) despite the improved start-up performance. To overcome this problem, the pitch regulation system is proposed in this paper for increasing the solidity. In most of the previous investigations, the effect of pitch angle was tested on low-solidity VAWT at uniform flow conditions and low turbulence intensity in wind tunnel test sections, which are different from the real conditions. In this investigation, the influence of pitch angle on the aerodynamic performance of a small Darrieus-type straight-bladed high-solidity VAWT equipped with a pitch regulation system is investigated numerically and experimentally under realistic condition. The proposed numerical procedure is validated through experimental test results. The COP is measured and calculated at different tip speed ratios and two pitch angles of 0 and 5°. The results reveal 25% enhancement in maximum COP with the increase of pitch angle up to 5°. Moreover, according to the numerical results, higher accuracy can be obtained at lower tip speed ratios for both pitch angles. Then, the numerical method is employed to calculate the power (performance) and torque coefficients as a function of Azimuth position as well as the flow field in rotor affected zone and lateral distance. It is found that increasing the pitch angle at a constant tip speed ratio is followed by accelerated vorticity generation, occurrence of maximum COP at lower tip speed ratio and smoother velocity profile in lateral distances of the rotor.

Visualization of aerodynamic forces and flow field on a straight-bladed vertical axis wind turbine by wind tunnel experiments and panel method

This paper investigated the evaluation of the aerodynamic performance and vortex characteristic of a straight-bladed Vertical Axis Wind Turbine (VAWT) in the spanwise direction. To observe the aerodynamic forces characteristics, pressures acting on the blade surface were measured by a multiport pressure measurement device. Pressure measurement was carried out in the spanwise sections of z/(H/2) = 0, 0.4, 0.70, 0.8 and 0.90 with wind tunnel experiments. Meanwhile, panel method based on the lifting surface theory was used to study the flow characteristics of VAWT. As a result, it was clarified that the absolute value of radial force coefficient from measurement took the maximum value at the upstream region around the azimuth angle of 100° and became small at the downstream region. Moreover, the radial force coefficient of the experimental value was significantly affected by the three-dimensional and decreased as it approached the blade tip. For the flow field, the circulation amount contour of the vertical vortex was wider near the blade center and became narrower around the blade tip in the blade spanwise direction. This study provided a better understanding of the development of aerodynamic forces and vortex characteristic through pressure measurements and panel method calculations.

Wind tunnel comparison of four VAWT configurations to test load-limiting concept and CFD validation

Abstract. The article describes results of experimental wind tunnel testing of four different straight-bladed vertical axis wind turbine model configurations. The experiment tested a novel concept of vertically dividing and azimuthally shifting a turbine rotor into two parts with a specific uneven height division in order to limit cycle amplitudes and average cycle values of bending moments at the bottom of the turbine shaft to increase product lifetime, especially for industrial-scale turbines. Testing reduction effects of simultaneously including a vertical gap between turbine rotor levels, increasing shaft length but also reducing aerodynamic interaction between rotor levels, has also been performed. Experiment results have shown very significant decreases of bending moment cycle amplitudes and average cycle values, for a wide range of measured wind speeds, for dual-level turbine configurations as compared to a single-level turbine configuration. The vertical spacing between levels equal to a blade's single chord length has proven to be sufficient, on laboratory scale, to limit interaction between turbine levels in order to achieve optimal reductions of tested parameters through an operating cycle shift between two position-locked rotor levels during a turbine's expected lifetime. CFD validation of maintaining the effect on industrial scale has been conducted, confirming the initial conclusions.

Effect of Pitch Parameters on Aerodynamic Forces of a Straight-Bladed Vertical Axis Wind Turbine with Inclined Pitch Axes

Pitch regulation plays a significant role in improving power performance and achieving output control in wind turbines. The present study focuses on a novel, pitch-regulated vertical axis wind turbine (VAWT) with inclined pitch axes. The effect of two pitch parameters (the fold angle and the incline angle) on the instantaneous aerodynamic forces and overall performance of a straight-bladed VAWT under a tip-speed ratio of 4 is investigated using an actuator line model, achieved in ANSYS Fluent software and validated by previous experimental results. The results demonstrate that the fold angle has an apparent influence on the angles of attack and forces of the blades, as well as the power output of the wind turbine. It is helpful to further study the dynamic pitch regulation and adaptable passive pitch regulation of VAWTs. Incline angles away from 90° lead to the asymmetric distribution of aerodynamic forces along the blade span, which results in an expected reduction of loads on the main shaft and the tower of VAWTs.

Effect of Helix Angle on the Performance of Helical Vertical Axis Wind Turbine

The energy crisis has forced researchers to look for various non-conventional energy sources. Wind energy is one of the potential sources, and researchers have invested resources in developing different kinds of wind turbines. Vertical axis wind turbines (VAWT) have received less attention than their horizontal-axis counterparts. A helical-bladed VAWT is preferred because it makes perfect sense as an improvement in design, as they have higher azimuth angles of power generation capabilities. This paper studies the effects of the helix angle of blades in the aerodynamic performance of VAWT using 3D numerical simulations. Three different helix angles of 60°, 90°, and 120° of a three-bladed VAWT operating across different tip speed ratios were studied. Turbulence is modelled using a four-equation transition SST k-ω model (shear stress transport). The 60° helical-bladed VAWT was found to be better performing in comparison with all other helical-bladed and straight-bladed VAWT. The ripple effects on the shaft are also analysed using a standard deviation plot of the moment coefficient generated by a single blade over one complete cycle of its rotation. It was observed that the greater the helix angle, the lower the standard deviation. The paper also tries to analyse the percentage of power generated by each quartile of flow and the contribution of each section of the blade. Ansys FLUENT was employed for the entire study. A comparative study between different helical-bladed VAWT and straight-bladed VAWT was carried out along with wake structure analysis and flow contours for a better understanding of the flow field.