Straight-bladed Vertical Axis Wind Research Articles

Novel performance enhancement of straight blade vertical axis wind turbines through cross-flow fan integration

In this study, a novel technique for enhancing the output power of Vertical Axis Wind Turbines (VAWTs) is introduced through the integration of a cross-flow fan (CFF) for active flow control, a first-of-its-kind approach. The CFF, positioned on the airfoil's trailing edge, employs suction to regulate flow separation. A thick airfoil with a 35% thickness-to-chord ratio is utilized to accommodate the CFF. A VAWT, featuring a diameter of 1 m and a height of 0.5 m, is designed, fabricated, and subjected to experimental testing in a wind tunnel. Additionally, a standard NACA 0018 wind turbine with identical dimensions and solidity is manufactured for performance comparison purposes. A custom test rig is developed to measure turbine output, encompassing a fixation mechanism, torque measurement system, and a mechanical brake mechanism for load variation. The impact of the CFF on the wind turbine performance is investigated by measuring turbine static torque due to the fan, fan motor power consumption, turbine torque, and rotational speed across various wind speeds. Power assessments are conducted to estimate the real turbine power increase, taking into account the power consumed by the fans. A fan map is generated to determine the optimal conditions and rotational speeds for fan operation.

Bio-inspired blades with local trailing edge flexibility increase the efficiency of vertical axis wind turbines

This experimental study is focused on quantifying the effect of trailing edge flexibility on the performance of a three straight bladed vertical axis wind turbine, with a chord-to-diameter ratio c/D=0.16 at a moderately high Reynolds number (based on diameter) ReD=4⋅105. The blades consist of NACA-0015 profiles that are fixed with a pitch angle β=6∘ toe-out, and allow interchangeable trailing edges in the last 17% of their chord length. The research presented here provides a proof of concept for the improved performance of vertical axis wind turbines, due to the effect of flexibility at the trailing edge of their blades. We show that blades with semi-flexible trailing edge, can extend the range of rotor operating regimes, leading to an increase of approximately 10% in the performance of the turbine. An excess of flexibility results in diminished efficiencies.

Analysis of Structural Vibrations of Vertical Axis Wind Turbine Blades via Hamilton’s Principle — Part 3: Pitch Angle and Equilibrium State

Pitch angle is one of the most important parameters of wind turbine blade. This study is aimed to investigate the effect of the pitch angle on the deformation of a VAWT. Lagrangian mechanics and Euler’s beam theory are used to derive the motion equations of linear structural vibration for straight blade vertical axis wind turbine blade with the pitch angle [Formula: see text]. The complete equations of motion take account of the 4-DOF deformation of flexural–flexural–torsion–extension as well as the material damping. Vibration analysis of generalized displacement about the equilibrium state (GDAES) is carried out with respect to the displacement of the equilibrium state (DOES), which is separated from the motion of vibration. After simplifying the equilibrium equation of 4-DOF into 1-DOF system, the exact solution of displacement [Formula: see text] of the equilibrium state is derived. The correction [Formula: see text] of [Formula: see text] due to the pitch angle and the characteristics of [Formula: see text] with constant linear speed are analyzed. Furthermore, we investigate the coupling effect of lateral bending and axial extension of the blade on [Formula: see text] is analyzed. Finally, the exact solution of [Formula: see text] is verified by the central difference method.

Design and fabrication of NACA 0018 straight bladed vertical axis wind turbine

The most important advantage in generation of electric power using renewable sources of energy, like wind, are the non availability of toxic exhaust emission products, highly uncluttered and the infinite presence of wind that is finally transformed into electricity. The generation and utilization of wind has been considered as one of the mature and cost effective resources among the various available renewable energy technologies. A wind turbine is a rotating machine that is converting the winds kinetic energy initially to mechanical energy, which finally getting converted into electric power. The wind turbines basically are of two types, i.e. Horizontal Axis Wind Turbine (HAWT) and Vertical Axis Wind Turbine (VAWT). The main point of difference between the two is the position of their axis of rotation. When wind blows over the VAWT, only a fractional part of the blades generates the torque whereas the remaining parts simply rotate. The end result of this is a comparably reduced efficiency in power generation. Here, a miniature Darrieus type VAWT with straight blade - NACA 0018 Airfoil, is designed and fabricated so as to develop maximum possible power output. The blades are designed in way were majority of the air covers majority of blade surface area and thus rotating it at its maximum possible speed. The results shows that the system we developed could produce power of 23.45 watts, with blades designed for aspect ratio of 0.24. This is the maximum possible result that can be attained for this dimension. The entire system is made of strong material so that it could also withstand high wind speed and high energetic wind possible.

Optimization of the power output of a vertical axis wind turbine augmented with a flat plate deflector

Power performance of a straight blade vertical axis wind turbine augmented with a flat plate deflector was studied. A design of experiment method based on Taguchi’s L16 orthogonal array was employed to optimize the position, orientation, and dimensions of the deflector. Five parameters, including the horizontal distance of the top edge of the deflector from the axis of rotation of the turbine (X), the vertical distance of the top edge of the deflector from the bottom of the blades (W), the length of the deflector (L), the width of the deflector (W), and the angle of the deflector with respect to the axis of rotation of the turbine (φ) were investigated. 16 three-dimensional numerical experiments were conducted to assess the effect of theses parameters on the power output of the wind turbine. Analyzing the results showed that the level of the influence of these five parameters can be ordered as φ>W>X>Y>L, which means that φ has the strongest impact on the performance of the wind turbine and L has the weakest impact. Utilizing the deflector with optimum parameters increased the efficiency of the wind turbine by 16.42% compare to the bare turbine.

Effects of blade shape and its corresponding moment of inertia on self-starting and power extraction performance of the novel bowl-shaped floating straight-bladed vertical axis wind turbine

In this paper, the effects of the blade shape and its corresponding moment of inertia on the performance of a novel bowl-shaped floating straight bladed vertical axis wind turbine (VAWT) have been investigated. A numerical method was developed and validated to accurately simulate the interaction between the wind and VAWT. Three inferential parameters, the starting time, mean power coefficient, and standard deviation of the aerodynamic force, were employed to evaluate the performance of the turbine with different blade shapes. Performance indicators including the self-starting capability, power extraction efficiency, and fatigue characteristics, were assessed. The results indicated that the VAWT with S-1046 blade had better overall performance as compared to the one with NACA0018 blade, where the reduced self-starting time, slight more or identical mean power coefficient, and minor standard deviation of Ft and Fn were observed. Further, the flow structure around the blade was also analyzed, it was found that at low wind speed (less than 6.0 m/s) separated vortex around the turbine is observed, whereas at high wind speed, attached vortex is observed. Fluctuation curves of power coefficient variation with tip speed ratio ‘λ’ were also noted for the wind induced rotation of VAWT. At low wind speed, the highest power coefficient amplitude was obtained when the turbine was at maximum tip speed ratio, whereas at high wind speed, the highest power coefficient amplitude was obtained when the tip speed ratio of the turbine was slight less than the maximum value. Based on these results, it is strongly recommended to apply thinner symmetry (S-1046) blade for designing VAWT.

Optimization of Straight-bladed Darrieus type vertical axis wind blade for low wind speed

Straight-bladed Darrieus blade is a type of vertical axis wind turbine that requires low wind speed to operate but is considered less efficient due to conventional blade geometry. To increase its performance by means of dynamic torque, the study used a statistical method, central composite design, through DesignExpert software. The computational fluid dynamics (CFD) through SolidWorks Reynolds-Averaged Navier Stokes Equation (RANS) k – epsilon turbulence model was used to simulate the Design of Experiments. The study was composed of two phases, namely 2D and 3D simulations. The 2D simulation studied the effect of varying the camber, camber location, and thickness to the dynamic torque, while the 3D simulation varied the blade height, rotor radius, and materials. The camber’s optimal conditions, camber location, and thickness in 2D simulations are 4.75%, 45%, and 15.50% of the chord, respectively. These optimal design values could reach the dynamic torque equivalent to 60.6571 Newton-meter. Meanwhile, the blade height and rotor radius of the 3D simulations have optimal design values of 4.41 meters and 4.75 meters, respectively. These optimal values could increase the dynamic torque to 2310.01 Newton-meter. The dynamic torque of the optimal design obtained a 133% significant increase compared to the conventional blade. Thus, the research has proven the increase in the Darrieus Wind turbine’s performance by varying its blade geometry.

AERODYNAMIC MODELS APPROXIMATE FOR ESTIMATING THE BLADE PERFORMANCE OF A DARRIEUS-TYPE CROSS-FLOW WATER TURBINE

The interest in studying windmills is that they are in the renewable energies context which had gained a great importance regarding to the world demand for energy that by 2050, could double or even triple as the global population grows [Vaughn, N., Wind Energy, Renewable Energy and the Environment, London: Taylor & Francis Group, 2009]. In this background, this paper represents a numerical investigation on a new vertical axis wind turbine (VAWT) (Darrieus type). The idea proposed was to have more blades on each side of a three-bladed VAWT and to examine how such a configuration would affect the machine's performance. The proposed H-rotor named Tandem turbine is numerically tested. Different configurations are tested to examine the pitch angle effect on the power coefficient (Cp). The validation of the numerical code was made through the comparison of numerical simulations with experimental study of a two-bladed VAWT performed by Laneville and Vittecoq (1986). The blades used are NACA0018. The turbulence model for calculations is the Spalart−Allmaras model. The power coefficients (Cp) have been calculated over a range of specific speeds A chosen between 1.75 and 4.35. Below the value of λ = 3, the tandem turbine with no pitch angle provides higher Cp than the conventional turbine [Kjellin, J., Bulow, F., Eriksson, S., Goude, A., Deglaire, P., Leijon, M., and Bernhoff, H., Power coefficient measurement on a 12 kW straight bladed vertical axis wind turbine, Renewable Energy, vol. 36, no. 11, pp. 3050-3053, 2011]. Such results encourage us to undertake more advanced work on this topic.

Vertical Axis Wind Turbine Aerodynamics: Summary and Review of Momentum Models

Momentum models or streamtube models represent one of the fundamental approaches in modeling the aerodynamics of straight bladed vertical axis wind turbine (SB-VAWT) of Darrieus type. They are based on momentum (actuator disk) theory and widely used in performance evaluation of VAWTs. In this short review, the authors have strived to compile the basic momentum models that have been widely assumed in the literature for design and performance estimation of SB-VAWTs of Darrieus type. A comprehensive demonstration of the formulation needed for the implantation of these models is also proposed. Three streamtube models are investigated in this paper, namely, the single streamtube (SST), the multiple streamtube (MST), and the double multiple streamtube (DMST) models. Each of these models has it merits and demerits which are also thoroughly discussed in this review.

Wind Tunnel Experiment and CFD Analysis on Performance of Straight Bladed Vertical-Axis Wind Turbine in Shear Flow

Wind Tunnel Experiment and CFD Analysis on Performance of Straight Bladed Vertical-Axis Wind Turbine in Shear Flow

Numerical Investigation of Power Output and Flow Visualization of Straight blade Vertical Axis Wind Turbine Integrated with Wind Accelerator

Numerical Investigation of Power Output and Flow Visualization of Straight blade Vertical Axis Wind Turbine Integrated with Wind Accelerator

Numerical investigation of the aerodynamic characteristics for the integrated vertical movable vanes with the airfoil straight blade vertical axis wind turbine

With the depletion of fossil fuels and the effects of fossil fuel emissions on climate change. The demands of the renewable energy is increasing. For these reasons, many researchers they are focused on harvesting renewable energy and reducing the use of fossil fuels. The vertical axis wind turbine (VAWT) is one type of the wind turbine that is widely used now a day. Low starting torque occurs when the airfoil is used in the straight blade vertical axis wind turbine as a blade. In order to increase the turbine starting torque, a flat plate vane type VAWT having movable vane is integrated with the airfoil straight blade VAWT in one rotor combination. In the present study, the numerical simulation is carried out to predict the aerodynamic characteristics of the combined three blades vertical axis wind turbine. A commercial available SolidWork2016 and computational fluid dynamic (fluent) software’s with k-ω turbulence mode are used in this simulation. The predicted results from the simulation show that the turbine starting torque is increased when the vertical movable vanes are integrated with the straight blade in the vertical axis wind turbine. The flow of air passes freely through the movable vanes in case of the vanes are fully open at the negative side of the turbine, this case helps to increase turbine rotation and so, thus, the power of the turbine increases. Finally, the predicted results from the simulation give a good agreement with those results reported in the published literature for VAWT has different blade configurations.

A Reduced Order Model to Predict Transient Flows around Straight Bladed Vertical Axis Wind Turbines

We develop a reduced order model to represent the complex flow behaviour around vertical axis wind turbines. First, we simulate vertical axis turbines using an accurate high order discontinuous Galerkin–Fourier Navier–Stokes Large Eddy Simulation solver with sliding meshes and extract flow snapshots in time. Subsequently, we construct a reduced order model based on a high order dynamic mode decomposition approach that selects modes based on flow frequency. We show that only a few modes are necessary to reconstruct the flow behaviour of the original simulation, even for blades rotating in turbulent regimes. Furthermore, we prove that an accurate reduced order model can be constructed using snapshots that do not sample one entire turbine rotation (but only a fraction of it), which reduces the cost of generating the reduced order model. Additionally, we compare the reduced order model based on the high order Navier–Stokes solver to fast 2D simulations (using a Reynolds Averaged Navier–Stokes turbulent model) to illustrate the good performance of the proposed methodology.

Measurement of Unsteady Torque Acting on Blades of Straight Bladed Vertical Axis Wind Turbines

Measurement of Unsteady Torque Acting on Blades of Straight Bladed Vertical Axis Wind Turbines

A novel heuristic method for optimization of straight blade vertical axis wind turbine

In this research study it is aimed to propose a novel heuristic method for optimizing the VAWT design. The method is the combination of continuous/discrete optimization algorithms with double multiple stream tube (DMST) theory. For this purpose a DMST code has been developed and is validated using available experimental data in literature. A novel continuous optimization algorithm is proposed which can be considered as the combination of three heuristic optimization algorithms namely elephant herding optimization, flower pollination algorithm and grey wolf optimizer. The continuous algorithm is combined with popular discrete ant colony optimization algorithm (ACO). The proposed method can be utilized for several engineering problems which are dealing with continuous and discrete variables. In this research study, chord and diameter of the turbine are selected as continuous decision variables and airfoil types and number of blades are selected as discrete decision variables. The average power coefficient between tip speed rations from 1.5 to 9.5 is considered as the objective function. The optimization results indicated that the optimized geometry can produce a maximum power coefficient, 44% higher than the maximum power coefficient of the original turbine. Also a CFD simulation of the optimized geometry is carried out. The CFD results indicated that the average vorticity magnitude around the optimized blade is larger than the original blade and this results greater momentum and power coefficient.

Numerical study of airfoil thickness effects on the performance of J-shaped straight blade vertical axis wind turbine

Numerical study of airfoil thickness effects on the performance of J-shaped straight blade vertical axis wind turbine

Influences of some parameters on the performance of a small vertical axis wind turbine

The effects of various parameters on the performance of a straight bladed vertical axis wind turbine, using the vortex model, have been numerically investigated. A vortex model has been used to evaluate the performance of a vertical axis wind turbine, by means of aerodynamic characteristics of different airfoils for Reynolds numbers between 105 and 106 . Parameters such as the thickness and the camber of the blade airfoil, the solidity, the type of blade profile, the number of blades and the pitch angle, which influence the power coefficient, C P , and the start-up regime. This study can be used in the designing an optimal vertical axis wind turbine in a specific location, when the prevailed wind regime is known.

Investigation on Darrieus type straight blade vertical axis wind turbine with flexible blade

In this study, a three-dimensional VAWT with a spanwise passively deformable flexible blade has been modelled. The study mainly focuses on the analysis of blade structure characteristics associated with the bending and twist deflection. Two types of flexible blade material and two strut locations supporting H-type blades are being investigated. The unsteady external loads and energy efficiency of VAWT with such designed flexible blade are also being analysed. The simulation results show that the bending and twist deflection peak is positively correlated with the turbine tip speed ratio λ. For a flexible blade, an unevenly distributed structural stress along the blade with a high stress regime in the vicinity of strut location has also been observed. Due to the rotational motion of a VAWT, the centrifugal force acting on VAWT blade plays an important role on the blade structure characteristics. Reduction of the blade stiffness results in an increase of the blade stress. Changing the strut location from middle to tip will cause a large area under high stress. The results also indicate that the VAWT with a highly flexible blade is not an efficient energy extraction device when it is compared to a less flexible or a rigid blade.

Numerical Study of Flow Field and Aerodynamic Performance of Straight Bladed VAWT at Variable Tip Speed Ratios

This paper studies the relationship between unsteady flow features and instantaneous torque and power performance of straight bladed vertical axis wind turbine at variable tip speed ratios. The rotor unsteady flow field simulation was carried out by using computational fluid dynamics method. The flow physics and the principle of changing flow field acting on torque performance and power performance have been analyzed where the rotating rotor was the major concern. The results show that the flow feature alters from periodical blade dynamic stall vortexes generation, development and shedding at low tip speed ratio to cyclical formation, evolution and diffusion of blade wake flow with the rising tip speed ratio. Both vortex shedding around the blade and interaction of blade wakes degrade the rotor aerodynamic performance. It is suggested that, to absorb maximum wind energy, delay the blade vortex shedding and reduce the range of blade wake, evolution and diffusion should be included in the rotor aerodynamic design.

Modeling dynamic stall of a straight blade vertical axis wind turbine

This paper investigates the development of the dynamic stall of a full straight blade vertical axis wind turbine (SB-VAWT) using computational fluid dynamic modeling for solving the 2D Navier–Stokes equations. The 2D unsteady Navier–Stokes equations are solved with the concept of Reynolds averaging. A mesh independency test is analyzed using the General Richardson Extrapolation technique. Two turbulence models are applied, namely the SST k−ω and the Transition SST models. It has been found that the stall development is extremely sensitive to the transitional modeling and small laminar separation bubbles will only be accurately predicted by accounting for the transition. However, the transition affects the overall turbine performance by up to 20% and delays the peak of the predicted torque by about 11°, and therefore it is crucial to include laminar-turbulence transition in the design and optimization process of SB-VAWTs.