Vertical Axis Wind Turbine Research Articles

Aerodynamic performance enhancement of a vertical-axis wind turbine by a biomimetic flap.

We improve the aerodynamic performance of a simplified vertical-axis wind turbine (VAWT) using a biomimetic flap, inspired by the movement of secondary feathers of a bird's wing at landing (Liebe 1979). The VAWT considered has three NACA0018 straight blades at the Reynolds number of 80000 based on the turbine diameter and free-stream velocity. The biomimetic flap is made of a rigid rectangular curved plate, and its streamwise length is 0.2cand axial (spanwise) length is the same as that of blade, wherecis the blade chord length. This device is installed on the inner surface of each blade. Its one side is attached near the blade leading edge (pivot point), and the other side automatically rotates around the pivot point (without external power input) in response to the surrounding flow field during blade rotation. The flap increases the time-averaged power coefficient by 88% at the tip-speed ratio of 0.8, when its pivot point is at 0.1cdownstream from the blade leading edge. While the torque on the blade itself does not change even in the presence of the flap, the flap itself generates additional torque, thus increasing the overall power coefficient. The phase analysis indicates that the power coefficient of VAWT significantly increases during flap opening to full deployment through the interaction with vortices separated from the blade leading edge. When the pivot point of flap is farther downstream from the leading edge or the flap operates at a high tip-speed ratio, the performance of the flap diminishes due to its weaker interaction with the separating vortices.

Enhancing darrieus wind turbine performance through varied plain flap configurations for the solar and wind tree

Plain flaps (PFs) significantly increase camber, enhancing lift and aerodynamic performance when deployed. In Darrieus Vertical Axis Wind Turbines (VAWTs), which perform efficiently in low-speed, turbulent wind conditions, structural modifications like PFs can improve efficiency. This study explores plain flaps with 10-20-degree deflections at different chord lengths to enhance the NACA 2412 aerofoil’s performance. Using Unsteady Reynolds-Averaged Navier-Stokes (URANS) equations and the Shear Stress Transport (SST) k-ω turbulence model, simulations were conducted across high (Re ≈ 2.71 × 105), medium (Re ≈ 1.35 × 105), and low (Re ≈ 5.4 × 104) Reynolds numbers (Re). The 0.7–10 and 0.8–10 configurations significantly improved torque and Cp. At a Tip Speed Ratio (TSR) of 2.5, the 0.8–10 configuration increased the Cp by 19.51% over the flapless NACA 2412 without PF. The 0.7–10 configuration achieved the highest Cp across all TSRs, while a three-blade setup improved Cp by 43% compared to four- and five-blade configurations. The modified blades demonstrated consistent torque gains across all Re, proving the effectiveness of blade shape modifications in enhancing VAWT efficiency, particularly under fluctuating wind conditions, indicating the potential of PF-modified blades in improving small-scale wind turbine performance in varied urban environments.

A Study on Wind Collection Effect of Vertical Axis Windmills

In recent years, global warming caused by greenhouse gasses such as carbon dioxide has become a concern. This has resulted in increased focus on environmentally friendly power systems. Consequently, renewable energy power generation methods, such as wind and solar power generation, have attracted attention. Wind power generation is expected to significantly increase in the future. However, in many inland areas in Japan, the average wind speed remains 6 m/s or less. In this study, we proposed the introduction of winglets and wind collectors (used in aircraft wings) into straight-wing vertical-axis wind turbines to improve their power generation efficiency. Field tests were conducted to confirm the effectiveness of the proposed method. Using winglets and wind collectors, the wind turbine rotation speed was increased at low wind speeds, which facilitated the generation of power. Moreover, it was confirmed that a wind turbine equipped with the proposed winglets and wind collectors could capture wind without its dispersal as it passed through the turbine.

Optimizing Duct Geometry for Micro-Scale VAWTs: Exploring Aerodynamics and Aeroacoustics with URANS and DDES Models

Among several advantages of the Vertical Axis Wind Turbines (VAWTs), such as the low cut-in speed, these turbines have lower efficiency compared to Horizontal Axis Wind Turbines (HAWTs). In order to increase the power of VAWTs, a novel approach is employed to address the aforementioned issue. In this study, a convergent-divergent duct (including three components: nozzle, diffuser, and flange) is used, and in the first step of this study, the angles and lengths of all duct components and throat width are optimized (in 3D configuration). In the optimization process, first, the design points are determined by the Design of Experiment (DOE) method, and for each design point, the flow field inside the duct is modeled by the Reynolds-Averaged Navier-Stokes (RANS) approach. Moreover, the objective function of this optimization problem is to maximize the velocity of the flow inside the duct. In the following, the general treatment of the statistical population is forecasted using the Response Surface Method (RSM), and the optimal duct is obtained using the Genetic Algorithm (GA). It is observed that the optimal duct increases the local wind speed up to 1.99 times (from 5 m/s to 9.94 m/s at the throat). Furthermore, a sensitivity analysis was performed on the duct components, which are the most effective parameters in increasing wind speed, nozzle angle, and nozzle length. In the second step, a Darrieus VAWT (with both 2D and 3D configurations) is numerically validated, and then this turbine is scaled-down and located in the optimal duct. The position and tip-clearance of a turbine within the optimal duct are investigated to find the best configuration for higher power generation. Subsequently, both the bare wind turbine and the ducted wind turbine undergo thorough aerodynamic and aeroacoustic analysis, using unsteady RANS and Delayed Detached Eddy Simulations (DDES) approaches, respectively. The results reveal a remarkable improvement in the aerodynamic efficiency (power coefficient increased up to 2.5 times) with the addition of the optimal duct, while the aeroacoustic performance of the system is compromised, leading to an increase in sound pressure level.

Predicting wind turbine energy production with deep learning methods in GIS: A study on HAWTs and VAWTs

The increasing global demand for renewable energy necessitates accurate forecasting methods to optimize wind energy production, particularly in regions with varying climatic conditions. This study addresses this need by utilizing advanced deep learning techniques and Geographical Information Systems (GIS) to estimate the energy output of wind turbines. Specifically, it focuses on predicting the energy production of both horizontal axis wind turbines (HAWTs) and vertical axis wind turbines (VAWTs) using a combination of Markov and Cellular Automata-Markov (CA-Markov) models, alongside deep learning methods such as long short-term memory (LSTM), LSTM-Wavelet, and Support Vector Regression (SVR). Additionally, the study evaluates the energy output of each turbine type, factoring in their construction costs within the study area. The analysis reveals significant variations in energy output over time, with maximum values increasing from 85,017 Wh in 2000 to 166,050 Wh in 2020 in the northern region, while minimum outputs also rose significantly. Projections for 2030 suggest that approximately 17% of the northern region experience a substantial increase in wind power potential. Among the forecasting methods, the LSTM-Wavelet hybrid model demonstrated superior accuracy, surpassing the 90% threshold, primarily due to its effective handling of data instability and noise reduction. This study underscores the potential of using sophisticated modeling techniques to enhance wind energy forecasting, contributing to more efficient energy management in regions with high energy demand and limited resources.

Numerical investigation of duct augmented vertical axis wind turbine with cambered airfoils

Numerical investigation of duct augmented vertical axis wind turbine with cambered airfoils

Design of an Active Axis Wind Turbine (AAWT) That Can Balance Centrifugal and Aerodynamic Forces to Reduce Support Infrastructure While Maintaining a Stable Flight Path

This study introduces a novel approach to wind energy by investigating a novel Active Axis Wind Turbine design. The turbine is neither a horizontal nor vertical axis wind turbine but has an axis of operation that can actively change during operation. The design features a rotor with a single blade capable of dynamic pitch and tilt control during a single rotor rotation. This study examines the potential to balance the centrifugal and aerodynamic lift forces acting on the rotor blade assembly, significantly reducing blade, tower, foundation and infrastructure costs in larger-scale devices and decreasing the levelised cost of energy for wind energy. The design of a laboratory prototype rotor assembly is optimised by varying the masses and lengths in a lumped mass model to achieve equilibrium between centrifugal and lift forces acting on the turbine’s rotor assembly. The method involves an investigation of the variation of blade pitch angle to provide a balance between centrifugal and aerodynamic forces, thereby facilitating the cost advantages and opening the opportunity to improve the turbine efficiency across a range of operation conditions. The implication of this study extends to different applications of wind turbines, both onshore and offshore, introducing insight into innovation for sustainable energy and cost-effective solutions.

CFD Analysis on Novel Vertical Axis Wind Turbine (VAWT)

The operation of vertical axis wind turbines (VAWTs) to generate low-carbon electricity is growing in popularity. Their advantages over the widely used horizontal axis wind turbine (HAWT) include their low tip speed, which reduces noise, and their cost-effective installation and maintenance. A Farrah turbine equipped with 12 blades was designed to enhance performance and was recently the subject of experimental investigation. However, little research has been focused on turbine configurations with more than three blades. The objective of this study is to employ numerical methods to analyse the performance of the Farrah wind turbine and to validate the findings in comparison with experimental results. The investigated blade pitch angles included both positive and negative angles of 7, 15, 20 and 40 degrees. The k-ω SST model with the sliding mesh technique was used to perform simulations of a 14.4 million element unstructured mesh. Comparable trends of power output results in the experimental investigation were obtained and the assumptions of mechanical losses discussed. Wake recovery was determined at an approximate distance of nine times the turbine diameter. Two large complex quasi-symmetric vortical structures were observed between positive and negative blade pitch angles, located in the near wake region of the turbine and remaining present throughout its rotation. It is demonstrated that a number of recognised vortical structures are transferred towards the wake region, further contributing to its formation. Additional notable vortical formations are examined, along with a recirculation zone located in the turbine’s core, which is described to exhibit quasi-symmetric behaviour between positive and negative rotations.

Advancements in Vertical Axis Wind Turbine Technologies: A Comprehensive Review

Advancements in Vertical Axis Wind Turbine Technologies: A Comprehensive Review

A study of Power Generation From a Traffic Tunnel Using Vertical Axis Wind Turbine

A study of Power Generation From a Traffic Tunnel Using Vertical Axis Wind Turbine

Study on a novel dual-row vertical axis wind turbine with J-Shaped blades by using numerical methods and optimization

ABSTRACT This study investigates the benefits of using J-shaped blades in a dual-row Darrieus wind turbine (DDWT), combining two innovative ideas whose simultaneous impact on the self-starting capability of Darrieus turbines has not been explored. The performance of the turbine was simulated using Computational Fluid Dynamics (CFD) and optimized using both the Taguchi method and a combined Machine Learning and Genetic Algorithm (ML-GA) technique. Three main operating parameters, including the tip speed ratio (λ), radial ratio (δ), and angular distance (ϕ) of dual-row turbines, were investigated across four levels using an L25 orthogonal array design. According to the Taguchi analysis, the impact of the parameters on the power output was ranked in the order of λ > δ > ϕ. After comparison, the optimized turbine predicted by the ML-GA technique was chosen due to the superior accuracy of the ML-GA approach compared to the Taguchi method. The optimal configuration of a DDWT with J-shaped blades was predicted at λ = 2.15, δ = 1.39, and ϕ = 75.36, with a Cp of 0.49 based on CFD simulations. Compared to the single-row wind turbine, the proposed turbine showed a significant increase of the Cp at low tip speed ratios resulting in a better self-starting performance.

Dynamic Formulation of the Double Multiple Stream Tube Model of Offshore Vertical Axis Wind Turbines

Abstract The paper proposes a novel algorithm to simulate Vertical Axis Wind Turbines in floating motion based on a low-fidelity approach. The conventional Double Multiple Stream Tube Model is formulated as a steady state model to deal with the inherent unsteady aerodynamics of VAWTs. The Double Multiple Stream Tube Model makes use of an average contribution of the blade passages over a revolution to solve the Blade Element Momentum equation. The model reduces the dependence of the solution (the induction field) to a space variable. Floating Vertical Axis Wind Turbines undergoes a variation of aerodynamic quantities according to wave periods, also different from the rotor period. This paper provides a new formulation of the Double Multiple Stream Tube Model to solve the turbine rotation in time and space, introducing the variation of the platform velocity and a revised approach to the downstream actuator disc. The most impactful parameter is found to be the wave frequency: wave periods at full-scale are lower than the ones of the turbine rotor, featuring optimal operating points at low tip speed ratios. The increase of the wave frequency highlights the differences of the average torque prediction for a single blade up to 10% between the unsteady and the standard formulation. In this context, the development of fast low-fidelity computational tools play a key role in the assessment of the preliminary designs of Floating Offshore Vertical Axis Wind Turbines and it will be used to optimise the aerodynamic design of the laboratory scaled model under surge motion.

Determination of angle of attack and dynamic stall loop in the complex vortical flow of a vertical axis wind turbine

To improve the vertical axis wind turbine (VAWT) design, the angle of attack (AOA) and airfoil data must be treated correctly. The present paper develops a method for determining AOA on a VAWT based on computational fluid dynamics (CFD) analysis. First, a CFD analysis of a two-bladed VAWT equipped with a NACA 0012 airfoil is conducted. The thrust and power coefficients are validated through experiments. Second, the blade force and velocity data at monitoring points are collected. The AOA at different azimuth angles is determined by removing the blade self-induction at the monitoring point. Then, the lift and drag coefficients as a function of AOA are extracted. Results show that this method is independent of the monitoring points selection located at certain distance to the blades and the extracted dynamic stall hysteresis is more precise than the one with the “usual” method without considering the self-induction from bound vortices.

Modelled Cost Reductions for the X-Rotor Offshore Wind Turbine

Abstract The XROTOR project is developing an innovative turbine (X-Rotor Concept - XRC) that is a Vertical Axis Wind Turbine (VAWT)/Horizontal Axis Wind Turbine (HAWT) hybrid. The objective of this paper is to assess the XRC Levelised Cost of Energy (LCoE), applying different sensitivity analysis to determine a realistic LCoE range. This will then be compared with LCoE estimates for three traditional HAWT drivetrain configurations to evaluate the potential cost savings for the XRC. The paper considers a hypothetical farm of 100x5MW XRCs on generic monopiles, 100km from shore and commissioned in 2030 with a 30-year project. Analysis uses the University of Strathclyde Operation and Maintenance (O&M) model and an LCoE tool developed by University College Cork to calculate results. Sensitivity analysis varies key cost driving elements and uncertain inputs including the O&M strategy, distance from shore and the financial assumptions to determine an optimised LCoE estimated range. Results for the XRC are then compared with estimates derived using the same methodology for the HAWT configurations. Analysis indicates that the novel design may facilitate cost reductions, reducing OPEX by removing heavy components that would require costly heavy lift vessels to maintain. It also removes the failure modes around the gearbox, multi-pole generator and yaw system. The XRC could also reduce the capital cost of drivetrains through a power take-off approach that does not require a gearbox or a multi-pole generation but achieves comparable levels of power conversion. Ultimately the XRC could achieve LCoE cost reductions of 10-19%, compared with the traditional HAWTs. Further savings are considered possible but require additional design and analysis that are outside the scope of this paper.

Power performance optimization of twin vertical axis wind turbine for farm applications

Twin Vertical Axis Wind Turbines (VAWTs) appear to be the potential candidates for enhancing the power density of wind farms. Earlier twin-VAWT studies were mainly focused on carrying out the parametric study of one or two twin-VAWT variables together while treating the other variables as fixed. Since twin-VAWT variables strongly influence each other, therefore, this approach led to reporting conflicting optimal combinations of twin-VAWT variables for optimizing its power performance. Furthermore, previous studies considered higher rotor solidities, which is not desirable from a power generation perspective and it also reduces turbine lifespan. Using L16 (45) Taguchi orthogonal array along with a modified superposition model, this research optimized the power performance of twin-VAWT considering together, solidity ratio (σ), pitch angle (β), wind direction angle (δ), turbine spacing ratio (S/D) and rotational direction (φ) of the rotor as design variables. Unsteady CFD was employed to ascertain the power performance of orthogonal array designs followed by the orthogonal analysis for the optimum tip-speed ratios (TSRs) and power coefficients. Based upon the relative impact of the design variables on the mean optimum TSR, the variables were ranked as: (σ) > (δ) > (φ) > (β) and (S/D). On the other hand, a different trend for the relative impact of the design variables on the power performance was found: (β) > (δ) > (σ) > (φ) > (S/D). The orthogonal analysis optimum twin-VAWT configuration showed a positive synergistic interaction at TSRs > 2.5 and negative synergistic interaction at TSRs ≤ 2.5 in comparison to its standalone counterpart. Moreover, the orthogonal analysis’s optimum twin-VAWT underperformed by 4.7 % when compared with the best orthogonal array design at their respective optimum TSRs, indicating a sub-optimal design resulting from Taguchi orthogonal analysis. The incapability of orthogonal analysis to include the interaction effects among variables resulted in the sub-optimal twin-VAWT design. Linear graph method highlighted the presence of strong interaction effects among the design variables. For five design variables with four levels each (45), a full factorial Design of Experiments (DoE) of 1024 cases was constructed to include the interaction effects. Signal-to-noise ratios of full factorial DoE cases were predicted by the modified superposition model. The highest predicted signal-to-noise ratio among 1024 cases identified the best orthogonal array design as the actual optimum twin-VAWT configuration. The increase in power efficiency of twin-VAWT in comparison to its standalone counterpart was observed as the TSR was increased with the maximum power enhancement by 23 % at TSR 4.25. Furthermore, the optimal twin-VAWT configuration exhibited an optimal TSR of 3.5, contrasting with the standalone VAWT's optimal TSR of 3.0. This shift extended the power performance envelope of the optimum twin-VAWT, allowing for energy extraction across a broader range of TSR values. The undertaken study highlights the prospects of twin-VAWTs for increasing the farm power density.

Novel passive flow control method using leading-edge prism-shaped cylinder: Performance enhancement of vertical-axis wind turbines

Due to periodic dynamic stall at low tip speed ratios (TSRs), vertical-axis wind turbines (VAWTs) experience notable performance challenges during rotation, which leads to fluctuations in torque and a decrease in energy capture. This research aims to boost the aerodynamic performance of Darrieus VAWTs by employing a leading-edge (LE) prism cylinder (PC) to enhance energy extraction. This novel small-scale device functions as a passive method for controlling flow separation, aiming to energize the boundary layer and adjust the pressure distribution on the blades. Its effectiveness depends on factors such as size, shape, and placement, necessitating careful optimization. A three-dimensional (3D) computational fluid dynamics (CFD) analysis, combined with Taguchi optimization and analysis of variance, is conducted to determine the optimal design parameters for the LE PC tool. This 3D CFD method captures the full complexity of flow dynamics, including vortex structures and wake behavior, leading to more accurate wind turbine performance predictions than two-dimensional (2D) CFD models. The results highlight the crucial role of PC size (Factor A), which contributes nearly 85% to the total contribution factor, while the angle of PC influence is minimal. The optimized rotor demonstrates a 36% increase in maximum average power coefficient (CP) compared to an uncontrolled rotor at TSR = 1.5. However, the effectiveness of this control method diminishes at higher TSRs because the blades encounter angles of attack below the critical stall angle throughout the rotation cycle, naturally preventing flow separation and making the flow separation control method unnecessary. The PC installed on the optimized blade delays flow separation to 55% of the blade chord length, compared to 40% for the base blade. Consequently, the rotor operates efficiently, ensuring consistent, and reliable power generation without flow separation issues.

Structural dynamic characteristics of vertical axis wind and tidal current turbines

Vertical axis turbines have received great attention in both offshore wind and tidal current energy communities considering their advantages of economic design and unidirectional operation. However, their commercialization process is rather slow compared with the development of horizontal axis turbines due to technical challenges resulting from higher loads from unsteady aero/hydrodynamic forces, centrifugal forces and gravity of the structures. These are mainly because, while the inherent unsteady tangential pulls and fatigue loads intensify the structural vibration, aggravating structural safety and fatigue life, the relationship between the geometric parameters and the structural responses of blades remains unclear. Therefore, in order to clarify this issue, in this study, we focus on the modal and transient analysis of vertical axis turbines using multi-body dynamics, geometrically exact beam theory and detached eddy simulation. We find that the natural frequency of the rotor is directly related to the ratio of blade length and arm length. The effect of arms cannot be ignored in the structural analysis of the turbine. Moreover, an increase of blade length intensifies the deformation and vibration of the turbine’s structure, making the turbine more prone to fatigue failure. This article is expected to extend the existing knowledge of wind and tidal current turbines and provide a reference for choosing proper design parameters and developing suitable-capacity vertical axis turbines.

Aerodynamic performance analysis of two new types of helical blades for vertical axis wind turbines

Aerodynamic performance analysis of two new types of helical blades for vertical axis wind turbines

Savonius wind turbine blade selection based on computational fluid dynamics

The Savonius vertical axis wind turbine is widely used because of its simple design and efficiency at low wind speeds. The next development is the mini multi-blade Savonius helical wind turbine. At this miniature size, the performance of a mini multi-blade helical Savonius turbine due to variations in the number of blades and its impact on the energy produced has not been investigated in depth. Therefore, adjustments to the size and number of blades need to be made to optimize the performance of this turbine. The research aims to obtain the performance of the Savonius type S wind turbine with 3 blades and 4 blades using the CFD (Computational Fluid Dynamics) method. The main dimensions of the simulation model are the shaft diameter of 0.008 m, the outer diameter of 0.24 m, the height of 0.4 m, and the number of blades 3 and 4. The inner diameter of the 3-blade turbine is 0.21 m while the inner diameter of the 4-blade turbine is also 0.21 m. Both turbine models are subjected to wind speeds of 4 m/s, 5 m/s, and 6 m/s. Based on the simulation results, a turbine with 4 blades has more optimal performance compared to the 3-blade type. At a wind speed of 6 m/s, the 4-blade Savonius helical turbine produces a rotation of 498,215 rpm and a maximum power of 6,129 watts. Meanwhile, the Savonius turbine with 3 blades at a wind speed of 6 m/s produces a rotation of 545,655 rpm and a maximum power of 4,390 watts. This difference in performance shows the importance of adjusting the number of blades in wind turbine design to achieve optimal efficiency. This research provides useful insights for the further development of mini helical Savonius wind turbines in various wind conditions

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.