Vertical Axis Wind Turbine Blade Research Articles

Analyzing dynamic stall on tubercle mounted VAWT blades: A simplistic experimental approach using an oscillating rig

Leading-edge tubercles, inspired by the flippers of humpback whales, are widely adopted passive flow control devices to enhance the aerodynamic performance of various lifting surfaces. This experimental study investigates the implementation of sinusoidal and triangular tubercles on H-type Vertical Axis Wind Turbine blades to analyze their effects on dynamic stall characteristics. Experimental tests were conducted using a specially designed oscillating rig to replicate blade motion at different reduced frequencies. The results reveal that tubercle blades exhibit a lower stall angle and maximum normal force compared to the baseline configuration. Moreover, the dynamic stall characteristics of tubercle blades are notably smoother, leading to reduced hysteresis losses. A variation in the tubercle amplitude-wavelength ratio further decreases hysteresis, albeit at the cost of reduced normal force generation. At the highest tested reduced frequency of 0.065, tubercles reduce hysteresis by up to 38%. Despite the reduction in normal force, tubercles effectively mitigate the effects of dynamic stall vortices, resulting in smoother stall behavior. The observed reduction in hysteresis can contribute to enhancing the turbine’s lifespan and increasing power production efficiency. This experimental approach provides a cost-effective alternative to more expensive methods for studying dynamic stall characteristics.

Vibration control of the straight bladed vertical axis wind turbine structure using the leading-edge protuberanced blades

This study investigates the impact of structural responses resulting from alterations in aerodynamic characteristics caused by incorporating leading-edge protuberance (LEP) blades in vertical-axis wind turbines (VAWTs) under various wind speeds. The current experimental investigation was conducted on a scaled-down straight-blade VAWT with multiple wind speeds at a fixed pitch angle and uniform blade configuration. The unsteady structural excitation caused by the decay of vortices due to the different aerodynamic loads and its effect on the VAWT structure is examined in great detail. The presence of counter-rotating vortices from the LEP profile, however, enhances the aerodynamics of the blades at higher angles of attack. It is crucial to understand the structural characteristics resulting from changes in aerodynamics. The paper presents the effects of the LEP on the structural excitation of the VAWT by analyzing the acceleration and displacement data obtained from the static structure of VAWT for various operational wind speeds. The results showed decreased acceleration and displacement amplitudes for the VAWT with LEP at medium and higher wind speeds. Significant aerodynamic and structural damping was observed in the VAWT with LEP blades. The results obtained were in close agreement with the time and frequency domains of the measured displacement and acceleration from the structure. The bidirectional vibration control was observed for the VAWT with LEP, which was found to have a reduction ratio of 70 %.

Drag reduction of lift-type Vertical axis wind turbine with slit modified Gurney flap

This study examines aerodynamic performance enhancement of Vertical Axis Wind Turbine (VAWT) blades with Gurney flap (GF) modified by slits. A quasi-3D computational fluid dynamics solution based on Reynolds-averaged Navier-Stokes model is employed to evaluate the effectiveness of slit GF blades, in particular the lift-to-drag ratio. The computational domain includes three pairs of GFs and slits combination along the blade span-wise direction to allow quasi-3D flow development while applying translational periodic boundary condition on the two end-wall boundaries. The inlet velocity is 9 m/s for a VAWT configuration with Tip Speed Ratios (TSRs) of 1.44, 2.64, and 3.3, respectively and each of these TSRs represents low, medium, and high regimes of TSRs. Simulation results have shown a significant 8% drag reduction for blades with slit GFs at medium range of TSRs, albeit with a 2% decrease in lift compared to blades with clean GFs. This improves the lift-to-drag ratio and enhances moment production. The power generation also shows increases of 1.5%, 6.5%, and 11.3% at low, medium, and high TSR regimes, respectively, for the analysed slit GF blades. The drag reduction is primarily attributed to the generation of small-scale vortices by the slit, dissipating large coherent flow structures more rapidly in the near wake-field.

Ameliorating a vertical axis wind turbine performance utilizing a time-varying force plasma actuator

Controlling wind flow on vertical axis wind turbine blades is an effective technique for enhancing their performance. Modern equipment such as plasma actuators have gained significant attention for their ability to control, and improve the flow behavior in wind turbines. Previous studies have primarily focused on investigating plasma actuators with constant force. In this study, plasma actuators with varying forces over time were applied to the turbine blades. An unsteady 2D model was used to analyze the wind turbine. The sliding mesh model was employed to simulate rotor rotation, and the SST k-ω\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$k-\\omega $$\\end{document} model was utilized for turbulence modeling. Initially, the performance of the clean turbine was examined. In the next step, the plasma actuators with different force waveforms were applied to the wind turbine blades, including constant, sine, cosine, positive ramp, negative ramp, pulse in the first half-cycle, and pulse in the last half-cycle waveforms. The results indicated that the cosine, and sinusoidal waveforms, led to the greatest improvement with 37.28% and 35.59% increase in the net energy produced by the turbine, respectively, compared to the baseline case.

Can bird, cetacean, and insect inspired techniques improve the aerodynamic performance of DU 06 W 200 airfoil applied in vertical axis wind turbines?

ABSTRACT To achieve a better aerodynamic performance of wind turbines, the selection of a proper airfoil plays a crucial role. Generally, aviation airfoils (such as the NACA series) were widely used in the design of wind turbine blades due to their aerodynamic characteristics. However, several studies have shown that there are a number of defects in the application of aviation airfoils for blade design, such as poor stall characteristics or incompatible performance at different Reynolds numbers. The aerodynamic performance and lift force of newly developed airfoils inspired by cetaceans, birds, and insects were numerically investigated by CFD in the range of Reynolds number of 1.2 × 105 to 1.7 × 105 and a range of angles of attack (from 0° to 25°). ANSYS Fluent and the Shear Stress Transport (SST) k-ω turbulence models were selected to analyse the pressure and velocity distributions around the airfoils. In addition, the aerodynamic efficiency was calculated for all different cases. For verification and comparison, DU 06-W-200 airfoil was also simulated under the same operating conditions. Results revealed that several of these new bio-inspired designs can increase the aerodynamic performance of the DU 06-W-200 airfoil by up to 24.7%, with the bird-inspired airfoils presenting the best performance among all designs, and the best options for the design of vertical axis wind turbine (VAWT) blades.

Effect of baffles on efficiency of darrieus vertical axis wind turbines equipped with J-type blades

This study investigates the effects of incorporating baffles in J-type bladed vertical axis wind turbines. The objectives are to analyze the behavior of vortices and their impact on turbine performance and to explore various locations for placing the baffles along the J-type blades. The 3D numerical simulations of the current study applies the sliding mesh techniques to better model the rotational motion of blades about the turbine axis with respect to the wind. The results show that mounting zero-thickness baffles over the tips of the blades effectively reduces vortex leakage, minimizes tip vortices, and increases the pressure differential across the sides of J-type blades leading to a significant improvement of the turbine performance. At low tip speed ratios (TSRs) of 0.5, 0.75 and 1, in particular, the torque generation in comparison with conventional NACA0021 straight bladed turbines has been improved by up to 49.5 %, 38.2 %, and 28 %, respectively. Considering a wide range of TSRs, on average, the implementation of baffles results in a 17.5 % increase in torque generation. The effect of the baffle thickness on generated vortices and their evolution along the course of flow is also investigated to show how the zero-thickness baffles improves the blade aerodynamics.

Multiple boundary layer suction slots technique for performance improvement of vertical-axis wind turbines: Conceptual design and parametric analysis

Vertical-axis wind turbines (VAWTs) are gaining attention for urban and offshore applications. However, their development is hindered by suboptimal power performance, primarily attributable to the complex aerodynamic characteristics of the blades. Flow control techniques are expected to regulate the flow on the blade surface and improve blade aerodynamics. In the present study, an effective active flow control technique, multiple boundary layer suction slots (MBLSS), is designed for VAWTs performance improvement. The impact of MBLSS on the aerodynamic performance of VAWTs is examined using high-fidelity computational fluid dynamics simulations. The response surface methodology is employed to identify the relatively optimal configuration of MBLSS. Three key parameters are considered, i.e., number of slots (n), distance between slots (d), and slot length (l), which vary from 2 to 4, 0.025c to 0.125c, and 0.025c to 0.075c, respectively. The results show that MBLSS positively affects the power performance and aerodynamics of VAWTs. Parameter n has the most significant effect on VAWT power performance and the importance of d and l is determined by tip speed ratios (TSRs). Tight and loose slot arrangements are recommended for high and low TSRs, respectively. The relatively optimal configuration (n = 2, d = 0.025c, l = 0.05c) results in a remarkable 31.02% increase in the average net power output of the studied TSRs. The flow control mechanism of MBLSS for VAWT blade boundary layer flow has also been further complemented. MBLSS can prevent the bursting of laminar separation bubbles and avoid the formation of dynamic stall vortices. This increases the blade lift-to-drag ratio and mitigates aerodynamic load fluctuations. The wake profiles of VAWTs with MBLSS are also investigated. This study would add value to the application of active flow control techniques for VAWTs.

Optimal Design of Anti-Icing Blunt Trailing-Edge Wind Wheel for H-Type Vertical Axis Wind Turbine Under Operating Conditions

Abstract A novel optimization method is developed for the design of an anti-icing blunt trailing-edge wind wheel of H-type vertical axis wind turbine (VAWT) based on the quasi-steady-state icing. The parametric expression of the airfoil is given using the mean camber and thickness functions, the blunt trailing-edge is constructed by the rotation and zoom of coordinates, and then through the aerodynamic design theory, the geometry control equations of the blunt trailing-edge wind wheel are established. The icing process using Solution and Icing modules is repeated at equal interval azimuths to obtain the ice on the wind wheel per revolution. The optimization model is solved using particle swarm optimization (PSO) algorithm integrated with computational fluid dynamics (CFD) method to maximize the wind energy utilization in both ice-free and icing conditions. Significant improvements are realized for flow and aerodynamic characteristics, confirming that the optimization method provides important guidance for an anti-icing design of VAWT blades.

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.

Vertical Axis Wind Turbine for Low Wind Speed Environment: Effect of Scoop Harmony Blade

The wind condition in Malaysia is in the low-speed category with an average speed of 1 ms-1 to 4 ms-1. Effect of ground level relies significantly on the wind speed distribution. Despite these conditions, it is less suitable for the development of horizontal wind turbine as an energy source. The obvious weakness is the lack ability to self-start and predict the wind direction thus affects the energy efficiency output. To overcome this problem, improvement of the vertical axis wind turbine design is observed to be the solution in replacing horizontal axis wind turbine. Hence, this study is to investigate a suitable type of vertical axis wind turbine blade design for the best performance RPM output in a low-speed wind environment. The investigation was conducted in a Longwin LW-9300R subsonic wind tunnel at 0 ms-1 to 10 ms-1 wind speed condition from three wind turbine blades specified as Solid Harmony, Scoop Harmony and Conventional Savonius blade with angle of 90º, 135º and 180º to determine the highest RPM productivity. Result shows that Scoop Harmony blade delivers the highest RPM blade output while Savonius 180º is seen to have the highest self-start blade achieved at 64 rpm at 1 ms-1 wind speed. However, Solid Harmony shows an acceptable range TSR of 0.5 with difference of 23% lower than Scoop Harmony. This shows that both Scoop Harmony has a higher performance RPM but Solid Harmony still has the potential design to be applied at low-speed condition due to its low TSR output.

Simulation Study of the Effect of Wind Speed and Material Type on the Mechanical Properties of Vertical Axis Wind Turbine Blades

Wind energy is a clean and fast-growing renewable energy source that can be harnessed using wind turbines. In a Vertical Axis Wind Turbine (VAWT), turbine blades are a crucial factor, and their fiasco leads to wind turbine failure. However, references to VAWT blade structural analysis are very limited. Therefore, the study was carried out to determine the material with the lowest degree of deformation without structural failure. The finding could be used as a recommendation in the material selection of Savonius type vertical axis wind turbine blades. The study used materials such as aluminum, stainless steel, and fiberglass. The analysis was carried out by simulating using ANSYS software. Computational Fluid Dynamics (CFD) was used for determining the loading by providing speed variations at 3 m/s, 4 m/s, 5 m/s, and 6 m/s. The Finite Element Analysis (FEA) method was applied to analyze the structure, which shows the results of total deformation, equivalent stress, and safety factor. The total deformation results from the aluminum blades showed values of 109.55 mm, 190.73 mm, 299.25 mm, and 425.39 mm. The safety factor values of 4.4049, 2.5166, 1.5647, and 1.1348 revealed that it was also technically safe. Aluminum material can be recommended to be used in the manufacture of Savonius type vertical axis wind turbine blades because of its low price, lightweight, corrosion resistance, and sufficient durability, as revealed from the results of total deformation and safety factor values.

Nonlinear Structural Vibration of Multi-Megawatt Vertical Axis Wind Turbine Blades-Part 1: Derivation of Motion Equations

Replacing fossil fuels with renewable energy is one of the important means to improve energy scarcity and environmental protection, and is of great significance for achieving sustainable development of human society. Vertical axis wind turbine (VAWT) is one of the key equipment for applying green energy — wind energy. During the operation of VAWT, its blades not only have to withstand periodic aerodynamic loads, but also suffer from centrifugal force effects and the Coriolis force effect caused by coupling with multi-dimensional deformation. The complex stress situation makes the blades susceptible to damage, resulting in structural resonance and instability of aeroelastic stability. This paper applies the Euler beam model and Hamilton principle to establish a nonlinear structural vibration motion equation for large-span vertical axis wind turbine blades with fully coupled four-dimensional deformation (i.e. lateral bending deformation, chord bending deformation, axial torsion deformation, and axial tensile deformation), and retains the nonlinear term of the motion equation to the third-order infinitesimal. Separating the motion equation into equilibrium equation and dynamic equation, it can be seen that the displacement of equilibrium state caused by the centrifugal force of the rigid body exists in the form of a coefficient in the dynamic equation, which will have an impact on the dynamic characteristics. This modeling work can provide a research foundation for exploring the dynamic characteristics and aeroelastic stability of VAWT blades in the future.

Blade strain analysis from field measurements on a vertical axis wind turbine

In this paper, the 10 kW WindQuest Vertical Axis Wind Turbine (VAWT) has been instrumented by strain gauges during its trials in the Ifremer in situ test site of Brest to study the effects of the structural dynamic response of the blades under operating conditions. Static and dynamic effects have been investigated as a function of the rotational speed when the rotor operates under stable wind conditions. The analysis segregates the influence of the gravitational, inertial, and aerodynamic loading components on the flapwise bending stress of the blades. The study of the cyclic variations on the blade strain at different Tip-Speed Ratios leads to the identification of the dynamic stall effect on the unsteady loads, while the spectral analysis describes the system eigenfrequencies excited by the interaction of the wind and the structure's motion. The results provide useful data to validate numerical models for VAWT blades with similar design and evaluate the structural fatigue.

On the estimation of the angle of attack for vertical axis wind turbines

PurposeThis paper aims to investigate the problem of estimating the angle of attack (AoA) and relative velocity for vertical axis wind turbine (VAWT) blades from computational fluid dynamics data.Design/methodology/approachTwo methods are implemented as function objects within the OpenFOAM framework for estimating the blade’s AoA and relative velocity. For the numerical analysis of the flow around and through the VAWT, 2 D unsteady Reynolds-averaged Navier–Stokes (URANS) simulations are carried out and validated against experimental data.FindingsTo gain a better understanding of the complex flow features encountered by VAWT blades, the determination of the AoA is crucial. Relying on the geometrically-derived AoA may lead to wrong conclusions about blade aerodynamics.Practical implicationsThis study can lead to the development of more robust optimization techniques for enhancing the variable-pitch control mechanism of VAWT blades and improving low-order models based on the blade element momentum theory.Originality/valueAssessment of the reliability of AoA and relative velocity estimation methods for VAWT’ blades at low-Reynolds numbers using URANS turbulence models in the context of dynamic stall and blade–vortex interactions.

Investigation of bamboo-based vertical axis wind turbine blade under static loading

Bamboo fiber composites are recyclable, low cost, high strength, and biodegradable compared to synthetic composites. Fiber-reinforced polymer composites such as glass and carbon fibers are extensively used as wind turbine blades followed by a major challenge of recycling and waste disposal etc. The present work investigates the suitability of bamboo-epoxy composite for vertical-axis wind turbine blades. The NACA 0015 and NACA 4415 blade profile has been chosen for study. The static structural analysis of blades is performed using various cross-ply and angle-ply layups. Results demonstrated that layup [45°/90°/0°/-45°]S obtained the minimum values of stress and deflection. The effect of shear webs is also analyzed. It is observed that the blade with two shear webs showed the minimum values of stress and deflection. The unidirectional strength of the composite material is also compared with the maximum design stress and found under acceptable limits. Additionally, the stress and deflection of the bamboo composite blades are compared with conventional blade materials. The stress and deflection on the non-symmetric bamboo-epoxy composite blade with double shear webs are obtained as 15.84 MPa and 4.45 mm which is observed to be decreased by 70.98% (stress) and 1.11% (deflection) respectively in comparison with glass-epoxy blade. Through the structural analysis, it is recommended that the designed blade with natural bamboo composite is acceptable for structural safety.

Energy Generation by Advanced Various Renewable Technology

Aim of this project is to production of electric energy using variable renewable technology, which is to be provided for the daily purpose. About 50% of the electricity used in India is generated by thermal power plants, which release a lot of toxic pollutants into the air and have a lot of negative environmental effects. Due to the high demand for electricity and the rising costs of coal and fuels, it has recently been noticed that there is an electricity crisis or shortage in India and other nations following the pandemic era. Since India is a nation that is constantly developing, there is a rising need for electricity. After all, coal is a type of fossil fuel whose supply will eventually run out, necessitating a shift to renewable technology. Over the road dividers, a vertical-axis wind turbine (VAWT) is being installed. As the car moves along the road, wind turbulence becomes trapped in the VAWT's blades, causing them to rotate and produce electricity. Additionally, we mount the solar panel over the VAWT, which generates electricity as well. When we apply this concept, a small hydroelectric power plant is built if there are nearby water bodies, such as ponds, rivers, dams, and water treatment facilities. A large amount of electricity can be generated by combining three renewable energy sources. It helps you reduce pollution in the atmosphere, earn carbon credits, and make energy generation economical. In our study, we found that about 0.5–1 KW of electricity can be generated in an hour, depending on the availability of wind turbulence and light intensity. This technology is capable of supplying electricity to one home

Blade Structure Analysis of 2 MW V-Shaped Vertical Axis Wind Turbine Using Numerical Simulation

The intensive research on large-scale Vertical Axis Wind Turbine (VAWT) couldprovide an alternative to Horizontal Axis Wind Turbine (HAWT) in offshore deployment for the future. Regarding this fact, this article develops a conceptual design of the VAWT blade structure and analyzes its feasibility using numerical simulation. The blade structure is designed for 2 MW Darrieus type V- shaped VAWT. The blade is tapered, 90m long, and inclined at 35° to the vertical axis. Initially, the blade design is tested for ultimate strength test according to IEC 61400-01 standard using aluminum alloy and homogenized composite material. In doing so, maximum aerodynamic loading on the blade is calculated after steady state 3-D RANS CFD simulation of the blade in ANSYS Fluent. The Finite Element Method (FEM) model of the blade is created using shell element in ANSYS Static Structural with structured meshing strategy, and tested with the aerodynamic load using the one-way Fluid-Structure Interaction (FSI) technique, to obtain mesh independent solution. The impact of the using 2, 3, and 4 number of shear webs is then analyzed on the selected mesh model of the blade. Finally, a four-shear web model of the blade is tested under extreme conditions. The thickness of the blade surface and shear web are varied to test maximum deflection at the tip, and maximum allowable strain of the blade. After obtaining the required blade structure, the deformation, maximum equivalent stress, and maximum equivalent strain for the blade are studied at rotation Tip Speed Ratio (TSR) of 5 under aerodynamic and gravitational loading, using both materials. The study showed significant deflection at the tip of the blade for the tower-less V-VAWT blade, suggesting an alternative support mechanism for the blade. Also, the study concluded that better structural robustness is achieved while using a composite material instead of an aluminum alloy. This article provides basis to study structural behavior of the novel V-VAWT blades and contribute to continuing research on obtaining optimized blade structure for such turbine.

Power enhancement of vertical axis wind turbine using optimum trapped vortex cavity

Vertical Axis Wind Turbine (VAWT) blades experience stall conditions at lower tip speed ratios during rotation, resulting in inefficient power performance. The power performance can be augmented by improving the blade's aerodynamic efficiency using active or/and passive flow control mechanisms. In this research, the power performance of 2-D H-type VAWT is enhanced by employing an optimum cavity on the suction side of the NACA 0018 blade airfoil. The optimum cavity shape was found using the Genetic Algorithm coupled with the Gaussian Process Regression (GPR) model at an airfoil static stall angle of attack in an isolated environment to reduce the computational cost of the optimization process. Two GPR models were employed to predict lift and drag coefficients, while the lift-to-drag ratio was used as an objective function in the optimization algorithm. 80 CFD runs were utilized for initial training and testing of the models, which reduced computational effort by 97% compared to a pure CFD-based optimization approach. The aerodynamic efficiency of the optimum cavity shape predicted by GPR models was also confirmed by CFD simulation, which showed only a 0.5% difference. For an airfoil with an optimum cavity, the aerodynamic efficiency was consistent at lower angles of attack. However, a significant rise of up to 31.8% was observed in the near stall region between 12° to 16° angle of attack in comparison to clean airfoil. The optimum cavity on baseline VAWT blades enhanced power performance by 63.8% at a TSR of 1.5. Moreover, at TSRs of 2, 2.5, 3, and 3.5, the enhancement in power performance was achieved by 34.4%, 22.2%, 16.1%, and 3.2%, respectively. This demonstrates the potential of employing an optimum cavity on the suction side for performance augmentation without applying the suction and a cost-effective solution by conducting optimization in an isolated environment.

Performance enhancement of an H‐Darrieus vertical axis wind turbine via moving surface boundary‐layer control

AbstractThe moving surface boundary‐layer control method (MSBC) is a kind of active flow control methods that overcomes the adverse pressure gradient and suppresses the flow separation by directly energizing the boundary layer near the moving surface. In this study, computational fluid dynamics simulations were performed to investigate the feasibility of using MSBC to improve the aerodynamic performance of a straight‐bladed H‐Darrieus vertical axis wind turbine (VAWT). In doing so, a segment of the original surface of the VAWT blade was then replaced with a moving surface. Influences of different geometric and motion parameters of moving surface, including location, length, velocity ratio, and groove depth on the net power coefficient of VAWT, were systematically studied. Moreover, the sensitivity of different parameters to the net power coefficient of VAWT at the optimal tip speed ratio was analyzed via the orthogonal design method. As a result, the optimal combination of moving surface parameters was able to be determined. The present results show that the maximum net power coefficient of VAWT having blades with partially moving surface can be increased by 22.8% compared with that of the baseline VAWT. In addition, the effectiveness of two active flow control methods, co‐flow jet and moving surface, in improving aerodynamic performance of a VAWT was also compared. It is found that MSBC method has the potential to achieve superior control performance and promote the energy utilization coefficient of the VAWT more effectively by using comparatively less external energy input.

Time scales of dynamic stall development on a vertical-axis wind turbine blade

Vertical-axis wind turbines are excellent candidates to diversify wind energy technology, but their aerodynamic complexity limits industrial deployment. To improve the efficiency and lifespan of vertical-axis wind turbines, we desire data-driven models and control strategies that take into account the timing and duration of subsequent events in the unsteady flow development. Here, we aim to characterise the chain of events that leads to dynamic stall on a vertical-axis wind turbine blade and to quantify the influence of the turbine operation conditions on the duration of the individual flow development stages. We present time-resolved flow and unsteady load measurements of a wind turbine model undergoing dynamic stall for a wide range of tip-speed ratios. Proper orthogonal decomposition is used to identify dominant flow structures and to distinguish six characteristic stall stages: the attached flow, shear-layer growth, vortex formation, upwind stall, downwind stall and flow reattachment stage. The timing and duration of the individual stages are best characterised by the non-dimensional convective time. Dynamic stall stages are also identified based on aerodynamic force measurements. Most of the aerodynamic work is done during the shear-layer growth and the vortex formation stage which underlines the importance of managing dynamic stall on vertical-axis wind turbines.