Small-scale Vertical Axis Wind Turbine Research Articles

Effect of blade pitching on power coefficient of small-scale vertical axis wind turbine at different tip speed ratios

This article analyses the effect of best blade pitching positions on the power coefficient of vertical axis wind turbine at different tip speed ratios. Analysis of the power coefficient of the vertical axis wind turbine is carried out for optimized six blade pitching curves. The first three pitching curves are designed for the tip speed ratios below 1.5 (0 < λ < 1.5) and other three are for the tip speed ratios in the range of 0 < λ < 3. The double multiple stream tube model is used for the present analysis. The results are compared between the optimized and sinusoidal pitching curves. It is concluded that the best optimized pitch position blade method improves the power coefficient than the typical sinusoidal blade pitching in the range of tip speed ratios 0 < λ < 3.

Effects of Offset Blade on Aerodynamic Characteristics of Small-Scale Vertical Axis Wind Turbine

A new way of connecting blade to rotor shaft named offset blade method was proposed for straight-bladed vertical axis wind turbine (SB-VAWT) in this study. In order to invest the efficiency of this method and effects of main parameters including offset length and blade airfoil on improving the output power performance and static starting characteristics, numerical simulations and wind tunnel tests were carried out. Four kinds of blade airfoil including NACA0012, NACA0018, NACA0024 and S809 were selected to analyze the influence of blade thickness and symmetry on SB-VAWT with offset blade. Numerical simulations were firstly carried out on output power for the rotor with 6 kinds of offset length for each airfoil. Wind tunnel tests were also carried out to compare with the results of simulations. The flow fields of rotor with different offset lengths were simulated and the effects of offset blade were analyzed. The optimum offset length among all studied for output power performance was found. Furthermore, the static starting torque and aerodynamic force characteristics of the rotor with optimum offset length were researched. According to the results, appropriate offset length can improve the output power characteristics and smooth the fluctuations of the static torque during one rotational period. The best offset length varies with the airfoil.

Airfoil selection and computational study on the torque performance of 4-blade vertical axis wind turbine

This paper contains numerically simulated data for a 4-blade Darrieus rotor type vertical axis wind turbine (VAWT). NACA0012, NACA0015, NACA0018 and NACA0021 airfoil types were analysed for the tangential force they create at different angle of attack. Based on the maximum tangential force generated by the airfoil for one full revolution, an airfoil series is selected for designing the 4-blade VAWT in simulation bed using Solid Works and then it is meshed, and cell zones are created over it in ANSYS tool. Then CFD analysis is carried out for different rotational speeds. Considering the overall torque produced during one full revolution, optimal rotational speed is arrived at. Finally, this study is aimed to study the torque performance of 4-blade Darrieus rotor type VAWT. This study is useful for designing the small scale VAWT for meeting the low energy demands at the load centres itself.

Benchmark of a Novel Aero-Elastic Simulation Code for Small Scale VAWT Analysis

After almost 20 years of absence from research agendas, interest in the vertical axis wind turbine (VAWT) technology is presently increasing again, after the research stalled in the mid 90's in favor of horizontal axis wind turbines (HAWTs). However, due to the lack of research in past years, there are a significantly lower number of design and certification tools available, many of which are underdeveloped if compared to the corresponding tools for HAWTs. To partially fulfill this gap, a structural finite element analysis (FEA) model, based on the Open Source multiphysics library PROJECT::CHRONO, was recently integrated with the lifting line free vortex wake (LLFVW) method inside the Open Source wind turbine simulation code QBlade and validated against numerical and experimental data of the SANDIA 34 m rotor. In this work, some details about the newly implemented nonlinear structural model and its coupling to the aerodynamic solver are first given. Then, in a continuous effort to assess its accuracy, the code capabilities were here tested on a small-scale, fast-spinning (up to 450 rpm) VAWT. The study turbine is a helix shaped, 1 kW Darrieus turbine, for which other numerical analyses were available from a previous study, including the results coming from both a one-dimensional beam element model and a more sophisticated shell element model. The resulting data represented an excellent basis for comparison and validation of the new aero-elastic coupling in QBlade. Based on the structural and aerodynamic data of the study turbine, an aero-elastic model was then constructed. A purely aerodynamic comparison to experimental data and a blade element momentum (BEM) simulation represented the benchmark for QBlade aerodynamic performance. Then, a purely structural analysis was carried out and compared to the numerical results from the former. After the code validation, an aero-elastically coupled simulation of a rotor self-start has been performed to demonstrate the capabilities of the newly developed model to predict the highly nonlinear transient aerodynamic and structural rotor response.

Comparison of simulations and wind tunnel measurements for the improvement of design tools for Vertical Axis Wind Turbines

As wind turbines are getting larger and cost reductions through up-scaling are reaching a limit, there is increasing pressure to reduce their installation and operating costs, making the business case for Vertical Axis Wind Turbines (VAWTs) more interesting again. However, in order to properly assess the economic potential of large-scale VAWTs, improved design tools are required. As the research budget for VAWT projects is generally too small to carry out expensive large-scale wind tunnel tests and field measurements, alternative methods are required. In this work, the application of small-scale, lower budget methods for improving VAWT design tools is assessed. It is shown that (a) currently available tools for VAWT design have not been sufficiently validated, (b) lower budget, small-scale wind tunnel tests can be effective for examining VAWT performance in terms of average power coefficient vs. tip speed ratio as well as the dynamics of the torque, and (c) Detached Eddy Simulations on small-scale VAWTs can be effective for examining their performance in terms of average power coefficient vs. tip speed ratio as well as the forces on the blades. Based on these results, a process for the transfer of the results of lower budget, small-scale measurements and simulations into recommendations for improved design tools is being developed.

Performance Evaluation of Small-Scale Vertical Axis Wind Turbine by Optimized Best Position Blade Pitching at Different Tip Speed Ratios

This paper analyzes and evaluates the effect of various design and operating parameters in the view of their influence on the starting turbine by itself, power coefficient and overall performance of the vertical axis wind turbine. Best pitch position of each blade in the rotation of turbine at different azimuth angles has been calculated at different tip speed ratios (TSRs) by using the aerodynamic analysis. Best pitch position of the blade is fixed at specific azimuth angle to produce the maximum tangential force in order to start turbine by itself and improve the power coefficient of the turbine. The double-multiple streamtube model is used for the present analysis. The results indicate that the best pitch position blade method improves the self-starting capacity and power coefficient. The best position blade pitching curve-1 with 45° pitch angle gives maximum power coefficient for TSRs of 1.0, and the best position blade pitching curve-5 with 15° pitch angle gives maximum coefficient of power about 0.53 for TSRs at 2.3. The results indicate that the optimized blade pitching with pitch variations from 45° to 10° improves performance of the turbine for TSRs 0 < λ < 3.

Aerofoil optimization for improving the power performance of a vertical axis wind turbine using multiple streamtube model and genetic algorithm.

This paper reports on the optimization of the NACA0015 aerofoil for improving the power performance of a vertical axis wind turbine (VAWT). The target range of the chord Re is 3 × 105–106, the tip speed ratio (TSR) is 2–6 and the solidity is 0.2–0.6. This aerofoil is widely applied in small-scale VAWTs. In the optimization process, in which the class and shape function transformation parametrization method was used to perturb the aerofoil geometry, the thickness and camber of the aerofoil were selected as the constraints and the value of the maximum tangential force coefficient was chosen as the objective function. The aerodynamic performance of the aerofoil was calculated by combining the XFOIL program and Viterna–Corrigan post-stall model, while the aerofoil's performance was validated with computational fluid dynamic simulations. The results illustrated that, compared to an unoptimized NACA0015 aerofoil, the optimized aerofoil's lift to drag ratio was improved over a wide range of attack angles and the stall performance was gentler. The maximum lift coefficient, the maximum lift to drag ratio and the maximum tangential force coefficient were increased by 7.5%, 9% and 8.87%, respectively. Finally, this paper predicted the rotor efficiency with both the unoptimized and optimized NACA0015 aerofoils for different TSRs and different solidities using the multiple streamtube model. The results showed that the rotor with the optimized aerofoil has a higher efficiency.

Wind tunnel experiments and Delayed Detached Eddy Simulation of a three-bladed micro vertical axis wind turbine

Abstract The present work attempts to study the performance of an Orthopter-type small-scale Vertical Axis Wind Turbine (O-VAWT) by means of wind tunnel experiments and numerical simulations. Experiments were conducted in an open circuit wind tunnel, where torque measurements were made at five different wind speeds for three different blade aspect ratios. A three-dimensional unsteady flow simulation utilizing the Delayed Detached Eddy Simulation (DDES), based on Spalart-Allmaras (SA) turbulence model [1], is employed for it possesses a good compromise between accuracy and computational demands. The capability of the DDES model in accurately predicting massively separated turbulent flow structures adjacent to turbine blades and performance coefficients are thoroughly assessed. Effects of wind speed, blade aspect ratio, and freestream inflow angle, on the performance of the turbine are carefully analyzed. Characteristics of turbine self-start and flow field adjacent to rotating blades with different aspect ratios and wind speeds are also investigated.

Experimental investigation of vertical-axis wind-turbine wakes in boundary layer flow

In this experiment, a small scale vertical-axis wind-turbine (VAWT) is immersed in a boundary-layer in a wind tunnel and stereo particle image velocimetry is employed to quantify the 3D characteristics of the wake. The measurements show that the wake is strongest behind the sector of the rotor which turns into the wind. Two counter-rotating vortex pairs in the wake induce crosswind motion which reintroduces streamwise momentum into the wake. Terms of the mean kinetic energy budget are computed and demonstrate that this crosswind flow has a significant influence on the redistribution of momentum in the wake. A similar analysis of the turbulence kinetic energy budget identifies shearing at the boundary of the wake as the primary contributor to the production of turbulence. An analytical model is developed in order to obtain a theoretical basis from which to understand how the aerodynamic behavior of VAWTs induces crosswind motion consistent with the production of counter-rotating vortex pairs.

Numerical Analysis of a Small-Size Vertical-Axis Wind Turbine Performance and Averaged Flow Parameters Around the Rotor

AbstractSmall-scale vertical-axis wind turbines can be used as a source of electricity in rural and urban environments. According to the authors’ knowledge, there are no validated simplified aerodynamic models of these wind turbines, therefore the use of more advanced techniques, such as for example the computational methods for fluid dynamics is justified. The paper contains performance analysis of the small-scale vertical-axis wind turbine with a large solidity. The averaged velocity field and the averaged static pressure distribution around the rotor have been also analyzed. All numerical results presented in this paper are obtained using the SST k-ω turbulence model. Computed power coeffcients are in good agreement with the experimental results. A small change in the tip speed ratio significantly affects the velocity field. Obtained velocity fields can be further used as a base for simplified aerodynamic methods.

Comparison of forecasting methods for vertical axis wind turbine applications in an urban/suburban area

Wind forecasting plays an important role in the economic benefit and system reliability of wind turbine power generation. The goal of the present study is to investigate different forecasting methods that can be used to improve the amount of energy captured by a small-scale vertical axis wind turbine (VAWT) operating in a gusty wind environment typical of an urban/suburban area. Four forecasting methods are studied in the present research: Persistence Method, Modified Persistence Method, Autoregressive Moving Average (ARMA) model, and Weather Research and Forecasting (WRF) model. The forecasting models are used to predict the wind conditions and optimal rotational speed of VAWTs located in Oklahoma City for data collected in 2009. In all cases, a constant rotational speed controller was used with a forecasting horizon of 1 day. The results indicate that a 5% increase in accuracy of the wind forecast could increase the total amount of energy captured by the VAWT by as much as 13%. The results also indicate that the use of a tuned speed adjustment factor (AF) in the modified persistence method improves the overall performance of the VAWT by as much as 6% compared to the persistence method. The value of AF was found to be site-independent and linearly proportional to the annual average wind speed. For the ARMA model, there exists an optimal amount of training data and forecasting horizon that results in minimal error when the forecasting data are compared to the actual data. For each of the sites investigated, the modified persistence method appears to slightly outperform the persistence, ARMA, and WRF models. In all cases, the forecasting models allow the VAWT to capture approximately 78%–85% of the optimal amount of energy that could be generated assuming the actual wind data were known in advance. The economic viability of the VAWT is also examined by comparing the Levelized Cost of Energy (LCOE) for the VAWT with the national electricity unit price. The LCOE of the system is competitive with the national electricity unit price at the sites where the annual average wind speed is 4.3 m/s or greater.

Experimental and numerical study of turbulence effect on aerodynamic performance of a small-scale vertical axis wind turbine

The suitability of vertical axis wind turbines (VAWTs) in harnessing energy within a complex wind environment has increased their renewed interest. However, there still exists a huge knowledge gap about the aerodynamic performance of VAWTs operating in a turbulent flow regime. In this paper, an experimental method is presented for a deeper understanding of unsteady rotor aerodynamics under turbulent flow operating conditions. To carry out the investigation, we developed and tested a small-scale Savonius turbine in a wind tunnel. A systematic analysis of torque and power coefficients, including their variations at uniform flow, was also presented to predict the power performance. A mechanism to generate a turbulent flow was then created to analyze the effect of induced turbulence intensity on the aerodynamics and performance of the VAWT. Results revealed that the turbulence of the inflow impacted fluctuating aerodynamic loads on the turbine blade and, ultimately, its aerodynamic performance. In addition, simulations using a CFD code were performed to compare numerical data with experimental measurements. This analysis shows the effect of turbulence intensity on performance of small wind turbines, and the aerodynamics that causes the behavior.

Aerodynamics of a Small-Scale Vertical-Axis Wind Turbine with Dynamic Blade Pitching

This paper describes the systematic experimental and computational studies performed to investigate the performance of a small-scale vertical-axis wind turbine using dynamic blade pitching. A vertical-axis wind turbine prototype with a simplified blade pitch mechanism was designed, built, and tested in the wind tunnel to understand the role of pitch kinematics in turbine aerodynamic efficiency. A computational fluid dynamics model was developed, and the model predictions correlated well with test data. Both experimental and computational fluid dynamics studies showed that the turbine efficiency is a strong function of blade pitching amplitude, with the highest efficiency occurring around to amplitude. The optimum tip-speed ratio depends on the blade pitch kinematics, and it decreases with increasing pitch amplitude for the symmetric blade pitching case. A computational fluid dynamics analysis showed that the blade extracted all the power in the frontal half of the circular trajectory; however, it lost power into the flow in the rear half: one key reason for this being the large virtual camber and incidence induced by the flow curvature effects, which slightly enhanced the power extraction in the frontal half but increased the power loss in the rear half. The maximum achievable of the turbine increased with higher Reynolds numbers; however, the fundamental flow physics remained relatively the same, irrespective of the operating Reynolds number. This study clearly indicates the potential for major improvements in vertical-axis wind turbine performance with novel blade kinematics, a lower chord/radius ratio, and using cambered blades.

Multi-objective design optimization strategies for small-scale vertical-axis wind turbines

Extracting energy from wind has been an interesting and serious topic over the last few decades and a lot of work has been done on the subject. This paper discusses in detail possible approaches to optimization of a somewhat less known type of wind turbines, particularly suitable for small consumers. In order to perform full aerodynamic and structural shape optimization of a small-scale vertical-axis wind turbine, a Double-multiple streamtube model code, known to provide good results in stationary working regimes, was complemented by a finite element analysis and implemented into a multi-objective particle swarm algorithm. For the purpose of shortening the total time needed for aerodynamic computation, the performed numerical simulations were two-dimensional and experimentally measured static airfoil data were used. The used aerodynamic model was validated against the available experimental data of similar wind turbines. The subsequent structural analyses of the composite turbine blades were performed by applying computed maximal aerodynamic forces together with gravitational and inertial loads. By employing various input and output parameters different multi-objective optimization strategies were analyzed and compared and their applicability was demonstrated. Investigated input parameters included: wind turbine rotor diameter, blade length, chord and airfoil, composite shell thickness, laminate lay-up and ply orientations, while optimization goal functions and constraints comprised rated power, cut-in and optimal wind speed, blade mass, tip deflection, failure index and blade natural frequencies. The fidelity and accuracy of proposed methodologies can be increased by employing more complex numerical models which can easily be implemented into the code.

Design and Analysis of Small-Scale Lift-Type Vertical-Axis Wind Turbine Using Composite Blade

This paper focuses on verifying the feasibility of applying fibre reinforced polymer matrix composite to vertical axis wind turbine. A small-scale lift-type vertical axis wind turbine using glass fibre reinforced epoxy matrix sandwich composite blade was proposed. An airfoil profile of blade was designed and a composite blade was fabricated. The structure parameters of the blade were optimized by means of the finite element modeling method. The mechanical and the resonant properties of the blade were investigated. Finally, a wind turbine with the designed blade was assembled, and its generating capacity was tested. It was demonstrated that the designed composite blade and the wind turbine had excellent performance, indicating a promising technology for utilizing wind power.

Aerodynamic design and analysis of a small-scale vertical axis wind turbine

Small-scale vertical axis wind turbines are regarded today as an attractive source of green energy, still insufficiently implemented and tested. This paper presents a fast design methodology of such a VAWT, in terms of choosing its main parameters: airfoil, rotor diameter and solidity. For obtaining generated power of each considered geometrical model at different undisturbed wind velocities and rotor angular velocities two models were used — momentum and vortex-wake model, combined with experimentally measured airfoil data (airfoil lift and drag coefficients). Even though the former model is simpler, it is the most utilized model, known to provide good results in stationary working regimes. Both models still present fairly accurate and fast tools for computation and optimization, particularly useful in the phase of conceptual design. In this research, the use of the momentum model resulted in determination of the maximal power coefficient, optimal- and minimal freestream velocity for every considered VAWT model. From these output parameters, a selection of the optimal geometric model was done, and a more detailed transient analysis and flow representation around the selected solution was obtained by the vortex-wake model. The results obtained by the two used computational models coincide satisfactorily.

반응표면법을 이용한 소형 수직축 풍력터빈 블레이드의 구조 최적화

The purpose of this paper is to perform the structural design of the small scale vertical-axis wind turbine (VAWT) blade using a response surface method(RSM). First, the four design factors that have a strong influence on the structural response of blade were selected. Analysis conditions were calculated by using the central composite design(CCD), which is a typical design of experiment for the response surface method(RSM). Also, the significance of the central composite design(CCD) was verified using analysis of variance(ANOVA). The finite element analysis was performed for the selected analytical conditions for the application of response surface method(RSM). Finally, a optimization problem was solved with a objective function of blade weight and a constraint of allowable stress to achieve a optimal structural design of blade.

Construct Small-Scale Vertical Axis Wind Turbine Monitoring System by Wireless Sensor Networks

The thesis proposes to construct a small vertical axis wind turbine monitoring system by the wireless sensor measuring network. This paper uses a small vertical axis wind turbine to generate electricity, and then provide to the parking lot and street lights, but also practical to monitor the entire system. Our monitoring system is constructed by the module. This paper proposes the small vertical axis wind turbine with the blade structure can be adjusted the angle with mechanical means, which is the most important improvement. Monitoring system to monitor real-time status of the communication part of the ZigBee and Ethernet established in the remote monitoring platform and the establishment of an Access database. Our research will be expected to improve the efficiency of wind turbine power generation, increase the stability of the monitoring system and the overall cost of power generation to reduce the effect.

Novel Experimental Power Curve Determination and Computational Methods for the Performance Analysis of Vertical Axis Wind Turbines

Through novel experimental and computational methods, this paper details a study into the performance aerodynamics of a small-scale vertical axis wind turbine (VAWT). A novel experimental method is first developed and validated before the results are compared to those of a computational fluid dynamics (CFD) study. The computational study is further validated by comparing the flow field to PIV data. The CFD simulations are then analyzed to explain the aerodynamics in further detail, including a discussion of the effect of the streamwise induction on the local angle of attack on the blade. The University of Sheffield’s three-bladed NACA0022 small-scale VAWT experimental rig is mounted within the University’s Low-Speed Wind Tunnel. Tests at tip speed ratios up to 5 were carried out, where the blade Reynolds number (based on rotational speed) ranged from 37,500 to 75,000. The same test conditions are simulated using unsteady computational fluid dynamics.

Improving Safety and Performance of Small-Scale Vertical Axis Wind Turbines

Although horizontal axis wind turbines (HAWT) are considered more efficient in operation than their vertical axis wind turbine (VAWT) counterpart and are more commonly used in wind farms as large wind turbines, the VAWT may offer greater advantages in safety and operation when it comes to their application within the urban environment. Yaw control systems are an essential requirement for the safe operation of HAWT, which are costly and require high levels of maintenance, but are inherently unnecessary for VAWT. At low blade speed ratios, the performance of VAWT degrades owing to strong dynamic stall effects. This necessitates VAWT operation at high blade speed ratios to suppress them. However, the consequent large rotational speeds lead to hazardous operation especially in confined urban areas. Thus to improve the low blade speed performance, a preliminary experimental investigation has been carried out at the Aerodynamics Laboratory of the University of New South Wales on an H-type VAWT blade that employed zero-net mass flux actuation. This technique has traditionally been used for static stall delay and flow separation mitigation on aircraft wings. In the present study, large relative angles of incidence were simulated by sinusoidally oscillating the blade about its quarter-chord, and resulted in the formation of dynamic stall vortices. The application of zero-net mass flux actuation was found to have a beneficial effect on the blade aerodynamic performance by either suppressing dynamic stall or delaying its onset to higher angles of attack. This study, therefore, suggests that reduced oscillatory loads and more robust output power can be achieved with zero-net mass flux actuation on VAWT operating at low blade-speed ratios. Consequently, the findings have positive practical implications for the design of small-scale VAWT for widespread use in the urban environment.