Darrieus Vertical Axis Wind Turbine Research Articles

Multi-objective optimization study on the performance of double Darrieus hybrid vertical axis wind turbine based on DOE-RSM and MOPSO-MODM

The Double Darrieus Vertical Axis Wind Turbine (DD-VAWT) effectively enhances wind energy efficiency at low tip speed ratios. In this study, the multi-objective optimization method is constructed for DD-VAWT. The optimization objective is to enhance the power coefficient as well as reduce the maximum instantaneous torque coefficient, while decision variables include the inner ring wind turbine diameter, inner ring wind turbine height, inner ring wind turbine blade airfoil chord length and inner and outer ring wind turbine phase angle. Firstly, the computational fluid hydrodynamics model of DD-VAWT is established and validated by experimental data from the literature. Then, the regression model between critical structural parameters and power coefficients, maximum instantaneous torque coefficients is constructed using response surface analysis. Finally, the multi-objective particle swarm optimization algorithm is used to optimize the objective and the optimal solution is selected from the Pareto frontier solution. This work provides a direction to improve the operating performance of DD-VAWT at low tip speed ratios as well as contributes to energy saving and emission reduction.

Computational fluid dynamics analysis on performance assessment of Darrieus-type vertical axis wind turbine using NACA0016, NACA0019 and NACA0020 airfoil sections

The efficiency of a vertical-axis wind turbine is remarkably less than a horizontal-axis wind turbine and consequently, the most important challenge of the former one is to enhance its aerodynamic performance. An earlier study shows that the selection of an efficient airfoil shape is an important criterion for enhancing the overall performance of a wind turbine. The objective of the present work is to perform the two-dimensional Computational Fluid Dynamics simulation of Darrieus Vertical axis wind turbine using NACA0016, NACA0019 and NACA0020 airfoils which are neither too thick nor too thin. Furthermore, the performance of these three airfoils is compared with two established airfoils, namely NACA0015 and NACA0018. The result reveals that the overall power coefficient of NACA0019 airfoils resulting from the CFD simulation is significantly higher than that of NACA0015. Therefore, the NACA0019 airfoil may be considered one of the effective alternative airfoils for the Darrieus VAWT. Highlights Simulation of vertical axis wind turbine using NACA0016, NACA0019 and NACA0020 airfoils Unsteady URANS studies are carried out to investigate the performance of the airfoils Among the blade profiles studied in this work, NACA 0019 offers superior fluid mechanical performance

A Numerical Study of Blade Geometry Effects in a Vertical-Axes Wind Turbines

Several geometrical elements influence the aerodynamic properties of the Darrieus vertical axis wind turbines (VAWTs). Many extant studies have examined properties, such as solidity, pitching axis position (x/c), length of chord (c), blade quantity (N), diameter (d) of the rotor, and aspect ratio. However, not many have examined the shape of the airfoil (AF), which is a vital property that remains to be thoroughly investigated. Therefore, this present study used computational fluid dynamics (CFD) to investigate many airfoils blade characteristics, such as blade thickness (BT), maximum camber ratio (MCR), MCR location (MCRL), and air speed (AS), to determine their impact on VAWT performance. The results demonstrate a blade thickness BT of 10 to 12%, MCR of 0 to 22%, and MCRL of 24 to 23% yield a comparatively high coefficient of power, adequate optimal blade rotation to airspeed ratio (TSR), broader operational area, and high band efficiency while air velocities of 15 to 10% yield a comparatively higher power coefficient.

Flow analysis and sensitivity study of vertical-axis wind turbine under variable pitching

The general frame of the present study falls under the umbrella of ongoing research and innovation in wind energy technology to improve the efficiency and reliability of vertical-axis wind turbines (VAWTs) in terms of design and control. While blade pitching is foreseen as a solution to minimize boundary layer separation and maximize the lift force during the entire cyclic blade operation (effectively enhancing the performances of VAWTs), conclusive research on active blade pitching mechanisms in low wind speed regions is limited because of the 3D complex aerodynamic around VAWT blades. The paper reports a holistic study on active blade pitching solutions to enhance the performance of H-rotor Darrieus VAWTs for different turbine design parameters, i.e., geometrical (different number and airfoil thickness, and solidity) under several operational conditions (Reynolds number (Re), and tip speed ratio (TSR)). In this study, a variable blade pitching technique, adapted for periodic variation of the angle of attack, is incorporated in a high-fidelity two-dimensional VAWTs transient Computational Fluid Dynamics (CFD) model to eliminate the dead band of small-scale wind turbines operating at low wind speed regions and increase the performance coefficient Cp at different TSRs. Sliding mesh and remeshing to capture the blade pitching are used to manage the rotor rotation. The CFD model is validated against experimental data from the literature. The results indicate that the local widening of the angle of attack (AoA) for each NACA0015 airfoil produces a Cp of 0.44, which represents 81% enhancement in the Cp at TSR of 1.5. Moreover, the study shows that increasing the number of blades or extending the blade chord length can eliminate the dead band of wind turbines. Furthermore, the maximum possible torque for 3- and 4-bladed rotor designs is achieved using the variable pitching mechanism.

Novel CFD and DMST Dual Method Parametric Study and Optimization of A Darrieus Vertical Axis Wind Turbine

The deteriorating effects of greenhouse gases resulting from the use of fossil fuels have led to increased public attention to renewable energy sources, with wind energy being a particularly favored option. This prompted the development of various wind turbine types' efficiency. This study intends to explore the influence of key design parameters consisting of the number of blades, blade chord length, helical angle, and J-shaped blade on the performance and self-starting ability of a Darrieus VAWT. Furthermore, implementing an efficient optimization model to obtain maximum power based on the numerical findings. To achieve this, two different numerical modeling approaches, namely Computational Fluid Dynamics (CFD) and Double Multi-Streamtube (DMST), have been applied. The results indicated that employing a higher blade number and chord length enhances the starting capability of the turbine. Moreover, increasing the helical angle to 60° reduces the generated torque fluctuations. Inspired by the design of the Savonius turbine, the implementation of a J-shaped airfoil boosted the Cp at low TSR. Finally, the Kriging optimization method has been employed to optimize the design parameters explored through CFD analysis. The outcomes showed that the optimum configuration of the examined Darrieus VAWT comprises a 3-bladed rotor with a blade chord length of 0.04 m and helical angle of 0° and a J-shaped blade length ratio of 0.68. This configuration yields an 10% increase in efficiency at the optimum TSR.

Investigation of the effect of critical structural parameters on the aerodynamic performance of the double darrieus vertical axis wind turbine

Double Darrieus Vertical Axis Wind Turbine (DD-VAWT) can efficiently capture wind energy at low tip speed ratios. In this work, the laws governing the effects of critical structural parameters, such as diameter of inner ring wind turbine, height of inner ring wind turbine, inner ring wind turbine blade airfoil chord length, and phase angle of inner and outer ring wind turbine, on the power performance and aerodynamic load are investigated. The power coefficient increases from 0.1670 to 0.2403 when the diameter of the inner ring wind turbine decreases from 1600 mm to 400 mm. The power coefficient increases from 0.1755 to 0.2135 when the height of the inner ring wind turbine increases from 600 mm to 1200 mm. The power coefficient increases from 0.1773 to 0.2135 when the chord length of the inner ring wind turbine blade airfoils increases from 0.15 m to 0.3 m. The power coefficient decreases from 0.2135 to 0.1976 when the phase angle of the inner and outer wind turbine is increased from 0° to 135°. Finally, based on Taguchi's experiments and grey correlation analysis, it is known that the most influential weight on the power coefficient and the maximum instantaneous torque coefficient is the airfoil chord length of the inner ring wind turbine blades, and the least is the phase angle of the inner and outer ring wind turbines. This work provides a reference for enhancing the DD-VAWT's performance.

Intracycle RPM control for vertical axis wind turbines

AbstractThe wind energy market is currently dominated by horizontal axis wind turbines (HAWTs); however, vertical axis wind turbines (VAWTs) are emerging as a design alternative, especially for deep‐water offshore siting due to their low center of gravity, ease of access to drivetrain components, and overall simplicity. Due to the absence of a pitch mechanism in large‐scale Darrieus VAWTs, stall control has often been used to manage power and loads. Introducing a pitching mechanism in H‐type VAWTs has been studied, but this diminishes the mechanical simplicity advantage, and the use of a pitching mechanism in a large‐scale Darrieus‐type VAWT is not practical. This work examines an innovative, alternative method to control the rotor dynamics of a large‐scale 5 MW VAWT to maximize power while constraining loads without introducing any new or complex mechanical elements. This control strategy is termed intracycle revolution per minute (RPM) control, where the rotational speed of the turbine is allowed to vary in an optimal fashion with the azimuthal location of blades as opposed to typical constant RPM operation. An optimization framework is formulated for an open‐loop optimal control problem and solved to maximize power subject to constraints on aerodynamic design loads. Results are presented to demonstrate the benefits and the performance limits of intracycle RPM control for large‐scale 5 MW Darrieus VAWTs, namely, (1) power production (quantified in terms of AEP) that can be increased subject to baseline load limits and (2) opportunities to significantly increase AEP or decrease loads via intracycle RPM control that are examined for both two‐bladed and three‐bladed VAWTs.

Leading Edge Radius Effects on VAWT Performance

Numerous studies have been conducted to investigate effect of blade geometry of vertical axis wind turbine performance. Most of the evaluations have focused on the airfoil series and airfoil geometry parameters such as thickness and camber of the airfoil. Few studies have examined the effect of other blade geometry parameters on the vertical axis wind turbine performance. In the present study, the effect of geometric change in leading-edge radius (LER) of a vertical axis wind turbine performance has been numerically studied. Hence, modified NACA 0021 airfoil profiles were created using the geometric method (CST). Then, the flow behavior around a Darrieus vertical axis wind turbine was simulated under the influence of the reduction and set-up coefficients of the leading-edge radius at a constant wind speed of 9 m/s and a tip speed ratio of 1.5 to 3.5 using the computational fluid dynamics. Additionally, the effects of the examined parameter (leading-edge radius) on fluid flow and aerodynamic performance coefficients, including the coefficients of power and torque, were investigated. The results indicated that the leading-edge radius affected the near wake flow of the turbine, and the optimization of leading-edge radius parameter controls the dynamic stall and reduces the formation of a vortex. Finally, the optimization of LER revealed that at 20% reduction in the LER the performance of the turbine at tip speed ratio of 1.5 was increased by more than 50%. This reinforces the self-starting capability of a Darrieus wind turbine.

Investigation on aerodynamic performance of H-type darrieus vertical axis wind turbine with different series airfoil shapes

Wind energy is one of the most important renewable energies since it reduces environmental pollution. Darrieus VAWTs with straight-bladed are more prevalent in small-scale power generation due to their simple blade design and easy construction. The investigation of the performance of VAWTs is a topic that is fascinating for Researchers to look into. Researchers have paid special attention to the Double Multiple Stream Tube (DMST) model for VAWT simulation because of the good correlation between the DMST model and the experimental results. In this paper Double Multiple Stream Tube analysis using Matlab programing to predict the aerodynamic performance of H-type Darrieus fixed pitch VAWT, More specifically, the power coefficient (Cp) and the tip speed ratio (TSR). The fact that an H-type Darrieus rotor has poor self-starting despite having a good power coefficient which is a constant worry at low wind speeds. Selection of the airfoil is one of the most essential factors to take into account while trying to enhancement the aerodynamic performance of H-type Darrieus fixed pitch VAWT. In this study first, results from experiments were used for the validation of the model, and then, 4 different families of symmetrical airfoils compared. The results indicate that the symmetrical airfoil S-1046 showed exceptional aerodynamic performance and a high starting torque for a low wind speed of 4m/s.

3D numerical simulation of the Darrieus vertical axis wind turbine with J-type and straight blades under various operating conditions including self-starting mode

A comprehensive three-dimensional numerical analysis is applied in this study to evaluate the competence of the J-type blades in the vertical axis wind turbines under wide range of operating conditions including various wind speeds, tip speed ratios and wind turbulence intensities. It is found that the vortices which are encapsulated in the concave part of the J-type blades escape from the tips of the blades and become stronger than those originated from the straight blades. Such strong wakes behind the J-type blades are responsible for larger negative effects on generating the torque at high tip speed ratios. Neither of the wind speed, nor the wind turbulence intensity have significant effects on performance of the J-type blade turbines. Of particular interest is to discover the behavior of the J-type blade under self-starting conditions which is a major shortcoming with Darrieus turbines. The results show that replacing the straight blades with the J-type blades causes the generated torque to increase by 26.9% and 37.6% at the wind speeds of 10 m/s and 5 m/s, respectively. Better performance of the J-type blades under self-starting conditions, makes them a promising candidate, especially at low wind speed regions such as urban areas.

Performance analysis of low Reynolds number vertical axis wind turbines using low-fidelity and mid-fidelity methods and wind conditions in the city of Nottingham

The aerodynamics of small-scale Darrieus vertical axis wind turbines (VAWT) is investigated at chord-based Reynolds number between 1 ×105 and 1 ×106. Initially, wind resource assessment is done for two locations in Nottingham, UK for 4 years. Both locations experience highly unsteady wind and the average wind speed is lower for the location within the city than outside the city. Next, two analytical aerodynamic methods are compared: low-fidelity Double Multiple Streamtube and mid-fidelity Lifting Line Free Vortex Wake methods. Five 3D design parameters are investigated: number of blades, blade shape, chord length, blade height and blade pitch angle. Overall, the power coefficient values and trends agree well between the two methods. The differences arise either in cases of very low solidity or high solidity. The unsteady flow field is visualized for each case using instantaneous vortices and streamwise velocity contours in the wake. The aim of the current work is twofold. Firstly, to investigate the difference between the two methods based on the physical principles modeled by each method. The second aim is to have a better understanding of the VAWT flow physics by studying the complex 3D force and flow field, and fluid dynamic interactions in the VAWT wake.

Toward improving the performance of a variable pitch vertical axis wind turbine (VP-VAWT), Part 2: Multi-objective optimization using NSGA-II with CFD in the loop

In this study, a multi-objective optimization is performed to improve the performance of a Darrieus vertical axis wind turbine (VAWT) at low tip speed ratios considering the aerodynamic and structural objectives. In this regard, firstly, a multi-objective optimization platform is developed. Using the results of part-1 of the current research, design of experiment (DOE) analysis, more effective design variables and their limited range of variation were extracted. These quantities were selected from pitch profile and blade section geometry variables, which will form a minimal optimization problem including the essential physics with reduced computational cost. The optimization is executed using a homemade NSGA-II code, validated by a benchmark model. It is embedded within the main MATLAB code, which relates and controls the flow field solution and optimization loop. Average moment coefficient in the downwind phase, the maximum moment coefficient in the upwind phase and the bending stiffness were selected as objective functions. These parameters would reflect power, structural fatigue and strength, respectively. The Pareto front charts are provided, which depict the relationship between objectives. It will then be followed by trend analysis and provide trade-off capability. Different aerodynamic aspects of the optimized VAWT are also compared with the reference VAWT, demonstrating the effects of optimum pitch profile and blade section. The trend analysis shows a compromise between structural and aerodynamic objectives, while the two indices of maximum moment and stiffness are not opposing. Moreover, a practical method for effective angle of attack identification is employed. Based on this estimation, one may deduce that the angle of attack in the upwind phase is more influenced by pitch variation than in the downwind. Interestingly, thrust coefficient and thrust angle variation range reduction would be achieved as a result of the proposed optimization, which is beneficial for the whole system's stability. According to the results, the developed framework is capable of performing other multi-disciplinary optimization challenges.

Novel hybrid blade design and its impact on the overall and self-starting performance of a three-dimensional H-type Darrieus wind turbine

The present study proposes a novel hybrid blade design that is the combination of a conventional airfoil, namely the NACA0018, and its J-shaped profile to increase the torque generation at the start-up stage of the turbine while decreasing the potential efficiency loss at the high tip speed ratios. Therefore, a new 2D-based design methodology was proposed, and depending on this methodology, different hybrid blade configurations were determined for the investigation of the overall and self-starting performance of the H-type Darrieus vertical axis wind turbine. Due to the inherent shape of the proposed hybrid blade, a 3D CFD dynamic start-up model, which is based on the fluid–turbine​ interaction, was built and used to evaluate the performance of the different configurations of the hybrid blades. The results indicate that although the proposed design methodology is based on the 2D-CFD calculations, it enables a quicker prediction of the aerodynamic performance of the proposed hybrid blades compared to the 3D-based CFD simulations. Furthermore, the findings also clearly illustrate that the new proposed hybrid blade designs not only overcome the self-starting issue of the turbine but also provide a wider turbine operating range and an improvement in the turbine peak efficiency in contrast to the losses caused by J-shaped airfoils.

Numerical investigation of h-Darrieus wind turbine aerodynamics at different tip speed ratios

PurposeThe purpose of the paper is to predict the aerodynamic performance of a complete scale model H-Darrieus vertical axis wind turbine (VAWT) with end plates at different operating conditions. This paper aims at understanding the flow physics around a model VAWT for three different tip speed ratios corresponding to three different flow regimes.Design/methodology/approachThis study achieves a first three-dimensional hybrid lattice Boltzmann method/very large eddy simulation (LBM-VLES) model for a complete scaled model VAWT with end plates and mast using the solver PowerFLOW. The power curve predicted from the numerical simulations is compared with the experimental data collected at Erlangen University. This study highlights the complexity of the turbulent flow features that are seen at three different operational regimes of the turbine using instantaneous flow structures, mean velocity, pressure iso-contours, blade loading and skin friction plots.FindingsThe power curve predicted using the LBM-VLES approach and setup provides a good overall match with the experimental power curve, with the peak and drop after the operational point being captured. Variable turbulent flow structures are seen over the azimuthal revolution that depends on the tip speed ratio (TSR). Significant dynamic stall structures are seen in the upwind phase and at the end of the downwind phase of rotation in the deep stall regime. Strong blade wake interactions and turbulent flow structures are seen inside the rotor at higher TSRs.Research limitations/implicationsThe computational cost and time for such high-fidelity simulations using the LBM-VLES remains expensive. Each simulation requires around a week using supercomputing facilities. Further studies need to be performed to improve analytical VAWT models using inputs/calibration from high fidelity simulation databases. As a future work, the impact of turbulent and nonuniform inflow conditions that are more representative of a typical urban environment also needs to be investigated.Practical implicationsThe LBM methodology is shown to be a reliable approach for VAWT power prediction. Dynamic stall and blade wake interactions reduce the aerodynamic performance of a VAWT. An ideal operation close to the peak of the power curve should be favored based on the local wind resource, as this point exhibits a smoother variation of forces improving operational performance. The 3D flow features also exhibit a significant wake asymmetry that could impact the optimal layout of VAWT clusters to increase their power density. The present work also highlights the importance of 3D simulations of the complete model including the support structures such as end plates and mast.Social implicationsAccurate predictions of power performance for Darrieus VAWTs could help in better siting of wind turbines thus improving return of investment and reducing levelized cost of energy. It could promote the development of onsite electricity generation, especially for industrial sites/urban areas and renew interest for VAWT wind farms.Originality/valueA first high-fidelity simulation of a complete VAWT with end plates and supporting structures has been performed using the LBM approach and compared with experimental data. The 3D flow physics has been analyzed at different operating regimes of the turbine. These physical insights and prediction capabilities of this approach could be useful for commercial VAWT manufacturers.

Numerical investigation on the helix angle to smoothen aerodynamic torque output of the 3-PB Darrieus vertical axis wind turbine

Numerical investigation on the helix angle to smoothen aerodynamic torque output of the 3-PB Darrieus vertical axis wind turbine

CFD Modeling of an H-Type Darrieus VAWT under High Winds: The Vorticity Index and the Imminent Vortex Separation Condition

This study introduces a Vorticity Index (VI) and an Imminent Vortex Separation Condition (IVSC), which are considered valuable indicators to quantify the vorticity impact on vertical axis wind turbines (VAWTs) operation. The VI and IVSC are specifically applied to a H-Darrieus vertical axis wind turbine (VAWT). Findings show that these two parameters display a direct relationship with the aerodynamic forces that govern the performance of this type of VAWT. This analysis is accomplished via 2D-CFD simulations of a H-Darrieus with a symmetrical NACA 0018, powered by high winds (8 and 20 m/s), by using a Shear Stress Transport SST k-ω model. The 2D model used is validated for Class II winds (8 m/s), for tip speed ratios (λ) ranging from 0.4 to 0.9. Power coefficients (Cp) predictions are close to those obtained with both 3D simulations and with experimental data, reported in the technical literature. It is found with the numerical simulations developed, that despite the significant increase of the average rotor overall torque values, when the wind speed is augmented from 8 m/s to 20 m/s, the energy extracted by the rotor seems to be moderately lessened by the amplified turbulence and vorticity.

Aerodynamic upgrades of a Darrieus vertical axis small wind turbine

Wind energy conversion is contributing significantly to the new clean energy transition but, up to now, such contribution is mainly driven by large multi-MW windfarms. On the other hand, the recent needs in terms of distributed energy production are revealing a new interest in small-scale wind energy conversion technologies for residential and urban applications. In this context, vertical axis wind turbines (VAWT) are often the most valid choice from the point of view of building integrating possibilities, but it is well known that they suffer a considerable gap in performance when compared to horizontal axis technologies. Based on these premises, in the present work some innovative solutions for improving the performance of a Darrieus vertical axis wind turbine are investigated through numerical and engineering approaches. The investigated interventions include rotor hybridization by the use of an inner Savonius section for improving the machine’s start-up and the possible application of dimples for improving the NACA 0021 airfoil performances on the outer rotor section. Results demonstrate the effectiveness of the interventions in obtaining a rotor with stable performances in a very wide range of wind regimes.

Investigation of a Newly Developed Slotted Bladed Darrieus Vertical Axis Wind Turbine: A Numerical and Response Surface Methodology Analysis

Abstract In the past few years, wind energy became the most reliable and clean energy source throughout the world. This research broadly has focused on the 2D design of the conventional (without slot) wind turbine blades as well as slotted airfoil blades for places having a low power density of wind. For vertical axis wind turbines, optimum airfoil design plays a vital role in the aerodynamic efficiency of the wind turbine. To get better aerodynamic efficiency, a feasible airfoil criterion of selection, played an important role in the chosen blade design. In this paper, the conventional NACA0018 profile without slots and slotted airfoil profile is selected for measuring the turbine blade performance. The geometry of the computational domain has been created using the solid works software and the computational investigation has been performed using the computational fluid dynamics (CFD) solver ansys fluent 2020 R2 with the help of the shear stress transport (SST k–ω) turbulence model. The simulations are conducted initially with base airfoil and then varying the different structures of slots. After introducing slots in the base airfoil, efficiency was increased in terms of lift coefficient (Cl) and power coefficient (Cp) by 2.32% and 17.94%, respectively at the angle of attack of 15 deg. The results indicate that slotted airfoils have a better lift coefficient and power coefficient compared to an airfoil without a slot. The best turbine operating parameters were found to be 14.82 deg of angle of attack, 1.73 coefficient of lift, and 2.99 tip speed ratio (TSR) by using the response surface methodology (RSM). At these optimal settings, the best Cp response was 0.406. A field experiment was carried out to verify the modeling-optimization outcomes, and the results were within 7% of the model projected results. Thus, this type of slotted airfoil designed for a vertical axis wind turbine (VAWT) can be used to harness wind energy potential more efficiently.

Numerical investigation of impact of hot climate conditions on the performance of Darrieus vertical axis wind turbine

Numerical investigation of impact of hot climate conditions on the performance of Darrieus vertical axis wind turbine

CFD-Based J-Shaped Blade Design Improvement for Vertical Axis Wind Turbines

The need for an increase in energy harvesting has led to novel ideas and designs to extract more power from wind. One innovative solution is through the use of J-shaped blades for Darrieus vertical axis wind turbines (VAWTs), which is based on the removal of a portion of a conventional blade, either on the pressure or suction side. Although improvements in the self-starting capabilities of VAWTs have been reported when using such blades, the literature only studied hollow blades, showing a hair-like structure. This work numerically investigates six different J-shaped designs. A turbine comprising NACA0015-based blades forms the base case and is used to evaluate the 2D numerical models. Results show that blades with an external cut systematically outperform those designed with an internal cut. In addition, all proposed cut-based designs are shown to improve the starting torque of the turbine, reaching a 135% increase compared to the base model.