Darrieus Vertical Axis Wind Turbine Research Articles

Enhancing wind energy harvesting performance of vertical axis wind turbines with a new hybrid design: A fluid-structure interaction study

Vertical axis wind turbines (VAWTs) provide promising solutions for wind energy harvesting in complex flow environment. However, it is challenging to guarantee satisfactory self-starting capability and high power efficiency simultaneously in a VAWT design. To address this challenge, a new hybrid Darrieus-Modifed-Savonius (HDMS) VAWT is designed and numerically tested using a fluid-structure interaction approach based on high fidelity computational fluid dynamics. A systematic study is conducted to analyze the effects of the moment of inertia, turbine structure, and external load on the self-starting capability and power efficiency. It is found that compared with the Darrieus VAWT, the HDMS design has better self-starting capability due to the torque provided by the MS rotor at small tip speed ratios (TSRs). The larger the MS rotor is, the better the self-starting capability is. However, there is penalty on power efficiency when the size of the MS rotor increases. With an appropriately sized MS rotor, the HDMS design can maintain high power efficiency comparable with the Darrieus VAWT at large TSRs. The key flow physics is that the HDMS design can keep accelerating at small TSRs due to the inner MS rotor, and can suppress dynamic stall on the Darrieus rotor at large TSRs.

Aerodynamic and aeroacoustic performance assessment of H-rotor darrieus VAWT equipped with wind-lens technology

The present paper investigates the aerodynamic and aeroacoustic characteristics of H-rotor Darrieus vertical axis wind turbine combined with a promising energy conversion technology, namely wind-lens, employing computational approaches. The Darrieus turbine adequate for low wind speed and urban area conditions. However, its aerodynamic and aeroacoustic characteristics are very complicated. Thus, the main scope of the current work is to enhance the aerodynamic performance of the introduced turbine and then assess the noise production accomplished with such enhancement. The studies are taken on two phases, the first phase is parametric 2D CFD simulations, employing the unsteady Reynolds-averaged Navier-Stokes (URANS) approach, to optimize the design parameters of the wind-lens. The second phase is a 3D CFD simulation of the full turbine using a higher order numerical scheme employing a hybrid RANS/LES method. An estimate of the aeroacoustic noise of the turbine is quantified using the Ffowcs Williams-Hawkings (FW-H) method. As a result, the optimal design parameters of the wind-lens are achieved and the optimized configuration shows a superior augmentation in power generated of about 82% increase in the power coefficient at a speed ratio of 2.75. However, the turbine equipped wind-lens produces more noisy operation compared to the non-shrouded turbine.

Steady wind performance of a 5 kW three-bladed H-rotor Darrieus Vertical Axis Wind Turbine (VAWT) with cambered tubercle leading edge (TLE) blades

Abstract The performance of a 5 kW three-bladed H-rotor Darrieus Vertical Axis Wind Turbine with cambered Tubercle Leading Edge NACA 0025 blades was established using computational fluid dynamics. 3D models and simulations of the VAWT were realized using CAD and CAE software, after which post-processing analyses provided understanding of the VAWT and blade flow physics. Results showed the TLE to be detrimental to flow and performance of a cambered VAWT. Using torque, lift and drag data, the cambered TLE VAWT was shown to deviate significantly against the cambered VAWT over one complete converged rotation. Cambered TLE VAWT blades encounter reduced lift forces and increased drag forces leading to lowered and eventual reversal of torque values. The z-vorticity and Q-criterion visualizations further supported the numerical results with the post-processed images showing vortices the size of the blade chord generated at blade wakes of the cambered TLE. The vortices emanate from the flow separation at the blade crests creeping in at the blade trailing edge at 75° azimuth and reaching halfway through the blade chord length at 106° azimuth. Spanwise separation was observed to be restricted at blade crests. The resulting flow degradation translated to the poor performance of the wind turbine.

Dynamic stall control on a vertical axis wind turbine aerofoil using leading-edge rod

Abstract The installation of a small rod in front of the leading edge of the symmetrical aerofoil as a passive control approach was proposed to control the dynamic stall of the Darrieus vertical-axis wind turbine (DVAWT). The flows around original NACA 0018 aerofoil and that with a rod were extensively simulated by solving the unsteady Reynolds-averaged Navier-Stokes equations with an SST k-ω turbulent model to investigate the effect of the rod on the dynamic stall control of the aerofoils undergoing Darrieus pitching motions. Numerical simulation results reveal that the counter-rotating vortices shedding from the rod continuously transmit kinetic energy into the boundary layer of the aerofoils. This mechanism prevents the formation of dynamic stall vortex and eliminates the flow separation of the aerofoils at large angles of attack. Parameter studies show that the diameter of the rod and the gap between the rod and aerofoil play an important role in stall control and performance improvement of the aerofoil. With the aid of the leading-edge rod, up to 210.9% relative increment of average tangential force coefficient for oscillating aerofoil and 42.1% relative increment of power coefficient for a two-bladed DVAWT were achieved at a tip speed ratio of 2.

On the use of Gurney Flaps for the aerodynamic performance augmentation of Darrieus wind turbines

Gurney Flaps (GFs) can enhance the aerodynamic performance of airfoils, making them generate more lift and delaying the onset of stall. Since their potential was discovered in the early ‘70 s, GFs have been applied in several fields, including wind turbines. Here, the research has been focused mostly on the use of GFs in Horizontal Axis Wind Turbines (HAWTs), whereas a lack of studies involving the application of these devices on Darrieus Vertical-Axis Wind Turbines (VAWTs) is apparent in the literature. The benefits induced by GFs could actually be particularly interesting for this type of wind turbines, which are presently receiving a renewed attention from the industry.In the present work, an extended numerical analysis using Computational Fluid Dynamics (CFD) was carried out with the aim of evaluating the potential of using Gurney Flaps for the power augmentation of Darrieus wind turbines.After a validation of the numerical approach using wind tunnel experimental data on a static airfoil, the simulations have assessed the impact of different GF mounting and height on board airfoils moving in the cycloidal motion typical of Darrieus wind turbines. The results on a single rotating airfoil allowed the analysis to highlight the physical phenomena taking place past the rotating blades, including the delay of stall and the modifications induced on the surrounding flow field; power enhancements higher than 20% were shown for some configurations. Then, impact of GFs on a real three-blade turbine was analyzed. The best configuration resulted in a 2%c GF installed in the inner side of the airfoil, so to have a better torque extraction in the downwind half of the revolution. The GF benefits were apparent especially at lower tip-speed ratios, suggesting its use both for newly-designed turbines and even as a retrofitting solution in existing rotors.

Static and Dynamic Analysis of a NACA 0021 Airfoil Section at Low Reynolds Numbers Based on Experiments and Computational Fluid Dynamics

The wind industry needs airfoil data for ranges of angle of attack (AoA) much wider than those of aviation applications, since large portions of the blades may operate in stalled conditions for a significant part of their lives. Vertical axis wind turbines (VAWTs) are even more affected by this need, since data sets across the full incidence range of 180 deg are necessary for a correct performance prediction at different tip-speed ratios. However, the relevant technical literature lacks data in deep and poststall regions for nearly every airfoil. Within this context, the present study shows experimental and numerical results for the well-known NACA 0021 airfoil, which is often used for Darrieus VAWT design. Experimental data were obtained through dedicated wind tunnel measurements of a NACA 0021 airfoil with surface pressure taps, which provided further insight into the pressure coefficient distribution across a wide range of AoAs. The measurements were conducted at two different Reynolds numbers (Re = 140 k and Re = 180 k): each experiment was performed multiple times to ensure repeatability. Dynamic AoA changes were also investigated at multiple reduced frequencies. Moreover, dedicated unsteady numerical simulations were carried out on the same airfoil shape to reproduce both the static polars of the airfoil and some relevant dynamic AoA variation cycles tested in the experiments. The solved flow field was then exploited both to get further insight into the flow mechanisms highlighted by the wind tunnel tests and to provide correction factors to discard the influence of the experimental apparatus, making experiments representative of open-field behavior. The present study is then thought to provide the scientific community with high quality, low-Reynolds airfoil data, which may enable in the near future a more effective design of Darrieus VAWTs.

INVESTIGATION OF NEW BLADE PROFILES FOR EFFICIENT LIFT VERTICAL AXIS WIND TURBINE AT LOW WIND SPEEDS

Ponte Academic JournalOct 2019, Volume 75, Issue 10 INVESTIGATION OF NEW BLADE PROFILES FOR EFFICIENT LIFT VERTICAL AXIS WIND TURBINE AT LOW WIND SPEEDSAuthor(s): Faris Alqurashi ,A. Dessoky, M. H. MohamedJ. Ponte - Oct 2019 - Volume 75 - Issue 10 doi: 10.21506/j.ponte.2019.10.3 Abstract:Darrieus turbine has attractive characteristics such as the ability to accept wind from random direction and easy installation and maintenance. However, its aerodynamic performance is very complicated and challenged. Darrieus turbine is one of the vertical axis wind turbines which is very promising type of wind turbines at remote and domestic locations that have low and weak wind potential and speed. But from the quantitatively comparison with horizontal axis wind turbines, this type of turbines has a weak performance. So, this paper introduces a numerical analysis of three-bladed Darrieus vertical axis wind turbine performance using 25 different sectional profile airfoils from different families. This investigation is to optimize and maximize torque output coefficient and output power coefficient. Aerodynamic simulations were used depending on finite volume analysis using computational fluid dynamic (CFD) methodology. These CFD simulations used the unsteady (transient) Reynolds-Averaged-Navier-Stokes (URANS) calculations to solve and analysis the flow field around the turbine. Quantitative and qualitative validation is presented in this work, it is found that an acceptable agreement between the current CFD calculations and the published experimental work in the calculations of the power output coefficient. The results presented that the best configuration is LS (1)-0413 airfoil. The power coefficient of the turbine consists of LS (1)-0413 airfoil has been increased by 16% compared to NACA 0021 performance Download full text:Check if you have access through your login credentials or your institution Username Password

Numerical simulation and research on improving aerodynamic performance of vertical axis wind turbine by co-flow jet

The co-flow jet (CFJ) based active flow control method is a new approach for suppressing the flow separation on the blade, delaying the stall, and enhancing the lift. In this study, a detailed numerical analysis of the flow field developing around a Darrieus wind rotor equipped with CFJ is presented in order to explore the effectiveness of CFJ in the efficiency improvement of vertical axis wind turbines (VAWTs). Unsteady Computational Fluid Dynamics simulations of the straight one-bladed and three-bladed rotors with the NACA0015 profile, using the shear stress transport (SST) k-ω turbulence model, were conducted. As a result, the effects of jet operational parameters such as the injection site and the momentum coefficient on the aerodynamic performance of the straight-bladed Darrieus vertical axis wind turbine (VAWT) have been comprehensively studied. The numerical results suggest that CFJ would be capable of recovering some of the power loss due to blade stall and its control effectiveness is more pronounced with the increase in the jet momentum coefficient. In addition, a power saving method for intermittent injection of a CFJ in accordance with the cyclic variation of the angle of attack is proposed and our results show that the stalling characteristics around a VAWT blade especially at low tip speed ratios can be considerably improved using intermittent CFJ which requires much less additional energy input.

A comprehensive analysis of aerodynamic flow around H-Darrieus rotor with camber-bladed profile

Improving the H-Darrieus rotor is often followed by the investigation of the influence of the turbine’s parameter design, notably, the aspect ratio, the solidity ( σ), the tip speed ratio, and the airfoil profile shape. In this work, we are interested in both the aerodynamic flows around a straight cambered blade profile and the rotor turbine wake separation of a Darrieus vertical axis wind turbine. The aim of this study is to better understand the evolution of the instantaneous torque and the generated-separated blade vortex during full rotation. Indeed, a three-dimensional computational fluid dynamics model of a vertical axis wind turbine with a straight cambered blade profile NACA4312 operating over a large range of tip speed ratio is considered. The flows are governed by Reynolds-averaged Navier–Stokes equations and the turbulence is modeled with shear stress transport formulations k- ω. This research revealed a high correlation between the evolution of the torque coefficient and the generated-separated blades vortex. In particular, a good correlation between the maximum tip vortices size and the torque coefficient peak is demonstrated.

Numerical determination of the nominal point of a wind turbine

The aim of this paper is to determine the nominal point of a Darrieus vertical axis wind turbine. In this study, two methods have been used. The first case used the DOF method, which requires the designation of the degrees of freedom of the turbine to ascertain the optimal revolution of the turbine for a certain speed of the wind. The second method relies on the unsteady analysis of the turbine for different tip speed ratios. A circular shaped domain was created using ICEMCFD, which was further divided in two subdomains. The first subdomain, the rotor, incorporates the blades and the shaft, while the second subdomain, the stator, represents the outer environment. A structured mesh was chosen for this study. The grid was generated using the blocking method. The chosen parameters for this study have the purpose of capturing the flow around the blades, and especially the boundary layer. For both cases, the variations of the moment coefficient were computed. By multiplying the mean of the moment coefficient with the tip speed ratio, we get the power coefficient. The results of this paper will be tested in a wind tunnel, using an experimental scale model of the turbine.

Effect of solidity on the performance of variable-pitch vertical axis wind turbine

The Darrieus vertical axis wind turbine (VAWT) has been the subject of a large number of recent studies to improve self-starting capability and aerodynamic performance. This study presents a computational fluid dynamics simulation of the vertical axis wind turbine with fixed and variable pitch at different solidities. In order to introduce the best efficiency value of solidity for a variable-pitch vertical axis wind turbine, a computational modeling of two-dimensional transient flow around a VAWT at solidities between 0.2 and 0.8 and turbine with two, three and four blades is conducted. The numerical simulation models the flow field around a turbine rotor by solving the strong nonlinearity of URANS and SST k-ω turbulence model, utilizing the semi-empirical numerical model. To simulate the turbine in a variable pitch method, the user-defined function (UDF) code and the moving mesh method are used. The results show that variable pitch blades with high solidities are preferred when the initial self-starting torque is required. Moreover, the variable pitch blades are capable to produce more torque at high solidities. Therefore, the vortex interaction between upwind vortices and blades in downwind stream is decreased. The results verify that the power reduction of fixed pitch VAWT at high solidities could be solved by utilizing the variable pitch technique.

DMST Approach for Analysis of 2 and 3 Bladed Type Darrieus Vertical Axis Wind Turbine

Wind energy has lately been one of the world's leading outlets of clean energy for producing power in potential environments across the globe. Academics currently undertake numerous analysis practices to improve and refine current wind turbine designs by means of advanced and diverse computational t

Structural Strength Analysis of a Tri-Floater Floating Foundation for Offshore VAWT

Vertical axis wind turbines (VAWTs) are advantageous for the development of large-scale offshore wind power because the drive system is located at the bottom of the turbine. This study investigates the structural strength of a tri-floater floating foundation supporting a 2.6 MW Darrieus VAWT. Finite element models of the floating foundation were developed using space plate-beam elements. The environmental loads, such as the aerodynamic loads, static wind loads, and wave-current loads, were considered. The general strengths of the floating foundation were calculated for the normal operating case (a cut-out wind speed of 25 m s−1 and blade rotation of 12 r min−1 were used to analyze the most unfavorable loads) and an extreme case (wind speed of 40 m s−1 and parked blades), and the weak components of the structure were analyzed. The results show that the floating foundation meets the strength requirements and the structural stress is highest when the wave, wind, and current are in a collinear direction. The main and secondary supporting bars transmit the loads between the stand columns and the tower foundation, and their stresses are higher than those in the other components. In the actual design, these supporting bars should be strengthened. The aerodynamic loads are very important and should be considered in the structural strength analysis of the floating foundation and the floating wind turbine system.

Combined experimental and numerical study on the near wake of a Darrieus VAWT under turbulent flows

Small Darrieus Vertical-Axis Wind Turbines (VAWTs) are presently seen as a relevant research topic for the wind energy community, since they are thought to perform better than horizontal-axis rotors in the complex and highly-turbulent flow typical of the urban environment. Indeed, a preliminary wind tunnel test campaign on a H-Darrieus VAWT showed a significant increase of the performance for high turbulence levels. The present study analyses in detail the near wake of the turbine in the same turbulent conditions, enabling a better insight on the reasons of this power increase, and on the means to take advantage of it. Near-wake measurements are also benchmarked with a CFD simulation of the entire wake, in order to match the experimental wake measurements with the detachment of flow structures observed in CFD simulations. By doing so, a deeper and useful insight on the reasons why VAWTs perform better in turbulent environments is gained.

Darrieus vertical axis wind turbines: methodology to study the self-start capabilities considering symmetric and asymmetric airfoils

Darrieus vertical axis wind turbines: methodology to study the self-start capabilities considering symmetric and asymmetric airfoils

Detailed Analysis of the Wake Structure of a Straight-Blade H-Darrieus Wind Turbine by Means of Wind Tunnel Experiments and Computational Fluid Dynamics Simulations

Darrieus vertical axis wind turbines (VAWTs) have been recently identified as the most promising solution for new types of applications, such as small-scale installations in complex terrains or offshore large floating platforms. To improve their efficiencies further and make them competitive with those of conventional horizontal axis wind turbines, a more in depth understanding of the physical phenomena that govern the aerodynamics past a rotating Darrieus turbine is needed. Within this context, computational fluid dynamics (CFD) can play a fundamental role, since it represents the only model able to provide a detailed and comprehensive representation of the flow. Due to the complexity of similar simulations, however, the possibility of having reliable and detailed experimental data to be used as validation test cases is pivotal to tune the numerical tools. In this study, a two-dimensional (2D) unsteady Reynolds-averaged Navier–Stokes (U-RANS) computational model was applied to analyze the wake characteristics on the midplane of a small-size H-shaped Darrieus VAWT. The turbine was tested in a large-scale, open-jet wind tunnel, including both performance and wake measurements. Thanks to the availability of such a unique set of experimental data, systematic comparisons between simulations and experiments were carried out for analyzing the structure of the wake and correlating the main macrostructures of the flow to the local aerodynamic features of the airfoils in cycloidal motion. In general, good agreement on the turbine performance estimation was constantly appreciated.

Pitch angle control for a small-scale Darrieus vertical axis wind turbine with straight blades (H-Type VAWT)

Unlike horizontal axis wind turbines (HAWTs), the Darrieus vertical axis wind turbine (H-type VAWT) has been the subject of only a few recent studies directed at improving its self-starting capability and/or aerodynamic performance. The technique currently used for improving the performance of this type of turbine is pitch angle control. This paper presents intelligent blade pitch control for enhancing the performance of H-type VAWTs with respect to power output. To determine the optimum pitch angles, ANSYS Fluent Computational Fluid Dynamics (CFD) software was used for a study of the aerodynamic performance of a 2D variable pitch angle H-type VAWT at a variety of tip speed ratios (TSRs). For each case examined, the power coefficient (Cp) was calculated and compared to published experimental and CFD findings. The results obtained from the CFD model were then applied for the construction of an aerodynamic model of an H-type VAWT rotor, which constituted a prerequisite for designing an intelligent pitch angle controller using a multilayer perceptron artificial neural network (MLP-ANN) method. The performance of the MLP-ANN blade pitch controller was compared to that of a conventional controller (PID). The findings demonstrate that for an H-type VAWT, compared to a conventional PID controller, an MLP-ANN results in superior power output.

A comprehensive analysis of solidity for cambered darrieus VAWTs

Wind energy technology has seen steady growth in the energy market as a clean, renewable source of energy. This has brought attention to areas with moderate wind energy potentials. Darrieus type Vertical Axis Wind Turbines (VAWTs) allow capturing of this potential for energy production at a cost-effective scale. To improve the performance of these turbines their design needs to be optimized. With better manufacturing methods currently available cambered blades are being investigated to improve the performance of these turbines. In particular, turbine solidity is investigated in this paper due to different airfoil chord lengths and different number of blades. The analysis is conducted following high fidelity CFD modeling in unsteady, turbulent regimes in Arbitrary Lagrangian Eulerian formulation accounting for the sliding/rotating rotor's domain configuration that emphasizes the role of rotor blades interaction. The study showed that low solidity turbines with cambered blades operate at low coefficients of performance (CP) over a large range of tip speed ratios (TSRs). High solidity turbines, with solidity close to unity, have much higher CP, but at smaller TSRs and a short range of TSRs. Medium solidity turbines, as well as turbines with solidity greater than unity, are faced with considerable interaction which compromises their operation at TSRs as low as one. The larger chord length helps improve the torque production of the turbine. The change in number of blades leads to a large dispersed wake behind the rotor which is unfavorable for deployment of an array of turbines.

Numerical investigation of dimple effects on darrieus vertical axis wind turbine

The Darrieus wind turbine is a type of vertical-axis wind turbines which, in spite of its simple structure, is very complex to analyze. In terms of aerodynamics, Darrieus VAWTs have properties which tend to make them distinctive of horizontal-axis wind turbines but generally are less effective. In the present research, a cavity is created into blade's profile of a VAWT to enhance its performance. The computational fluid dynamics have been used to simulate the turbine in turbulent flow and finally calculate the forces affecting it. The shear stress transport (SST) k-w turbulence model has been used to complete the governing equations and the turbine has been modeled in two dimensions. In order to enhance efficiency and aerodynamic performance of the turbine, effects of different dimple parameters including diameter, profile and its location has been considered. The optimum airfoil state has been found with circular dimple with diameter equal to 8% of cord length located on pressure side of the airfoil and near the leading edge. Eventually, it was observed that the efficiency at optimal performance (λ = 2.6) and average efficiencies of the turbine were 18% and 25% improved when using the airfoil with a cavity, as compared to the reference airfoil.

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

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