Optimal Wind Turbine Research Articles

A hybrid DMST model for pitch optimization and performance assessment of high-solidity straight-bladed vertical axis wind turbines

Straight-bladed vertical axis wind turbines (SBVAWTs) with a fixed pitch are subject to continuous variation in wind attack angle, which leads to low power generation. Variable pitch techniques are thus required to tackle the problem, but a proper analytical tool for pitch optimization and performance assessment must first be determined. This study thus aims to find a proper analytical tool for high-solidity SBVAWTs of low operational speeds for real-world applications. The applicability of the double-disk multiple stream-tube (DMST) model, a mainstream tool for analyzing moderate-solidity SBVAWTs and optimal pitch angles, is first examined for high-solidity SBVAWTs using measurement data obtained from wind tunnel tests. The complex flow field around a high-solidity SBVAWT is found to make current DMST models’ predictions unsatisfactory. A hybrid DMST model, using the attack angle-dynamic aerodynamic force coefficient relationship, is then proposed. The proposed hybrid DMST model predicts the aerodynamic forces acting on the blades with greater accuracy than those from current DMST models. Based on the proposed hybrid DMST model, a method of determining optimal pitch angles is developed and applied to the high-solidity SBVAWT. The results show that the novel method has the potential to significantly enhance power generation in high-solidity SBVAWTs.

The optimization and the application for the wind turbine power-wind speed curve

An optimized wind turbine power-wind speed curve (P-v curve) was presented in this paper to solve the problems in the low-wind-speed regions like the large wind speed variation and the low wind turbine efficiency. When the wind speed was lower than the cut-in wind speed, the operation mode of the wind turbine was changed by the extra power supplied by the motor excitation source to keep the wind turbine operating. The application condition of the optimized P-v curve was derived and calculated. The effects of various wind speeds on the powers and the power generation of the wind turbine were analyzed by comparison with and without the improvement. The results indicated that the prolonged working period, the improved efficiency of the wind turbine and the incremental power generation were induced by the usage of the optimized P-v curve. The cut-in wind speed was declined by 42.8%. The power generation was enhanced by 73.4% at the actual wind condition of some wind field. The motor power was augmented with the huge amplitude of the wind speed. Compared with the traditional P-v curve, the optimized P-v curve was more suitable for the lower average and larger amplitude of the wind speed.

Blade design for horizontal axis wind turbine: 3D model.

Wind energy is one of the best important sources of renewable energy and an excellent alternative for the transition to sustainable energy that the planet earth needs. The wind energy is contained in the air particles in movement, forming kinetic energy. This energy could be transformed into another type of energy such as electricity, through the use of wind turbines. It is known that horizontal axis wind turbines are more efficient energetically, the power output of a horizontal axis wind turbine depends of it aerodynamic performance; therefore, the correct geometric design of the propeller is essential for an optimum wind turbine. This article analyzes the most relevant aspects in the design of a wind propeller, using MATLAB® software to illustrate its behavior, suggests an ideal airfoil for wind applications to use in the 3D modeling of the blades using the computer assisted design, this blades has been built with a 3D printer.

Demand factor definition—A dimensionless parameter for Vertical Axis Wind Turbines

The use of dimensionless numbers like Reynolds Number, Froude Number and Webber Number has historically simplified the process of comparison of phenomena irrespective of their scales and in their classification into different categories. This paper deals with the derivational aspects of a dimensionless parameter named “Demand Factor” for optimization of Vertical Axis Wind Turbine (VAWT).•The input parameters considered in this derivation are power, wind velocity, the aspect ratio of the turbine, density of air and viscosity of air and the output parameters are length of the blade, number of blades, chord length, aerofoil shape, radius of the turbine and angular velocity at rated speed.•Four rounds of variable definition trials are carried out through the arrangement of the input parameters on the numerator and denominator positions. With the filtering out of unsuitable combinations at different stages of elimination, out of 32 combinations the expression that holds the potential to represent demand factor was identified. The process of carrying out single point optimization based on Demand factor expression is discussed along with the steps involved in numerically calculating output parameters.•The expression of Demand factor developed provides a different perspective on the process of design and optimization of VAWTs.

Numerical efficiency evaluation of a vertical axis turbine equipped with 4 digits and 5 digits NACA airfoils

In the current age of global energy crisis, a run for the use of renewable energy resources as the wind energy has gained a significant attention. The main objective of this study is the comparison between two wind turbine configurations. These two turbines have the same geometric parameters but one with a 4 digits NACA0018 blades and the other with 5 digits NACA63-415 blades. In this scientific paper, a numerical evaluation of the airfoil shape influence on the VAWT efficiency is done. For this study the CFD methods with Ansys Fluent software, are used. All the simulations are for unsteady flow at 1e06 Reynolds number value with SST turbulence model. At the design point the wind velocity is 12 m/s and for the wind turbine geometric features, the diameter is 3.25m and the height 4.87m. The power coefficient variation through tip speed ratio will be represented for each wind turbine configurations. To estimate the recirculation zone effects on the efficiency, the vorticity magnitude contours are presented for different positions of the blades. The results will indicate the feasibility of optimization of future wind turbine more complex airfoils.

Analysis and implementation of a drag-type vertical-axis wind turbine for small distributed wind energy systems

This article investigates a drag-type vertical-axis wind turbine that is targeted for small-scale wind energy system applications. Based on aerodynamics models, the three-dimensional simulation studies have been carried out to obtain the force distributions along blades and eventually the torque and power coefficients for different vertical-axis wind turbine configurations. An optimal vertical-axis wind turbine configuration is chosen based on the comparative analysis, and a 2 kW prototype system has been implemented based on the design. The effectiveness of the three-dimensional models and simulation results has been verified by the measured data from the actual vertical-axis wind turbine system. The wake impacts to the vertical-axis wind turbine caused by nearby objects are also analyzed. The simulation results and the actual operation experiences show that the proposed system has the characteristics of low cut-in speed, high power density, and robustness to adjacent objects (such as buildings and other wind turbines), which make it suitable for small-scale wind energy systems in populated areas including urban environment.

Operation of Stand-Alone Microgrids Considering the Load Following of Biomass Power Plants and the Power Curtailment Control Optimization of Wind Turbines

Various stand-alone hybrid power systems are widely used to fulfil the electric loads for remote, rural villages. Although there are many investigations based on various aspects of renewable hybrids energy microgrids, the discussions about the application of biomass combustion power plants are rare. Also, detailed investigations of the system steady and transient stability analysis, and the power curtailment control optimization of wind turbines in these stand-alone hybrid systems are seldom found. This paper focuses on wind/biomass/diesel/battery stand-alone microgrids and discusses the system operation, energy management and dispatch issues detailed. The renewable and controllable biomass power is localized to follow the load fluctuations over a long timescale to decrease the power production from diesel and the peak-load shifting demands of the battery banks. An optimization strategy of the wind power curtailment control is also proposed to effectively decrease the frequency and amplitude of the pitch actor and, to some extent, improve the power generation through the combination of the active turbine speed control and pitch regulation. Then a parallel double-mode optimal operation strategy with a “fault detector” is presented to realize economic optimization dispatch under the normal mode and emergency power control for large disturbance scenarios. Finally, case studies of a microgrid on a remote Canadian aboriginal community are conducted to demonstrate the performance of the proposed methods.

A case study: Small scale wind turbine system selection and economic viability

Increasing electricity production costs coupled with rising energy prices drive people to become energy independent. Wind energy systems can be one of the most cost-effective home-based renewable energy systems. A small-scale wind turbine can reduce the electricity bill slightly or up to 100% depending on the quality of wind resource of the site. More people across the world are seeking a solution against increasing electricity rates and a way to harvest their local wind resources. The aim of the study is to analyse an economic viability of a small-scale wind turbine system for residential use in southern Turkey. For this objective, firstly, an actual onsite wind data is evaluated. Five different on-grid small-scale wind energy production system alternatives which required to meet the electricity demand are offered. Performance of each turbine are examined; cost and benefit analysis based on cash flow, net present value, levelised cost of energy and payback periods are calculated. Recommendations are provided to the investor to make a decision on the optimum wind turbine selection based on performance and economic viability for the given site. At last, an overview of what is feasible on the preferred site is presented.

Optimal Irregular Wind Farm Design for Continuous Placement of Wind Turbines with a Two-Dimensional Jensen-Gaussian Wake Model

Optimal design of wind turbine placement in a wind farm is one of the most effective tools to reduce wake power losses by alleviating the wake effect in the wind farm. In comparison to the discrete grid-based wind farm design method, the continuous coordinate method has the property of continuously varying the placement of wind turbines, and hence, is far more capable of obtaining the global optimum solutions. In this paper, the coordinate method was applied to optimize the layout of a real offshore wind farm for both simplified and realistic wind conditions. A new analytical wake model (Jensen-Gaussian model) taking into account the wake velocity variation in the radial direction was employed for the optimization study. The means of handling the irregular real wind farm boundary were proposed to guarantee that the optimized wind turbine positions are feasible within the wind farm boundary, and the discretization method was applied for the evaluation of wind farm power output under Weibull distribution. By investigating the wind farm layout optimization under different wind conditions, it showed that the total wind farm power output increased linearly with an increasing number of wind turbines. Under some particular wind conditions (e.g., constant wind speed and wind direction, and Weibull distribution), almost the same power losses were obtained under the wake effect of some adjacent wind turbine numbers. A common feature of the wind turbine placements regardless of the wind conditions was that they were distributed along the wind farm boundary as much as possible in order to alleviate the wake effect.

Optimizing wind turbine's maintenance policies under performance-based contract

A sound maintenance policy of wind turbine occupies an important position in reducing the operations and maintenance (O&M) costs. However, few papers consider system performance, e.g. system availability, reliability, mean time to failure, into the maintenance policy. A novel optimal maintenance policy based on the performance-based contract (PBC) is presented to maximize the profit of suppliers meanwhile improving the system availability. Here, three maintenance actions are adopted: opportunistic maintenance, preventive maintenance and corrective maintenance. In precious researches where the objective was to minimize the O&M costs or maximize the system availability, while in this paper the maximum profit was used. To compare the proposed policy with conventional policies, three criterions are presented: maximum profit, greenhouse gas emissions and system availability. Finally, an illustrative numerical example is provided to demonstrate the applicability and superiority of the proposed model.

Variable-fidelity shape optimization of dual-rotor wind turbines

PurposeDual-rotor wind turbines (DRWTs) are a novel type of wind turbines that can capture more power than their single-rotor counterparts. Because their surrounding flow fields are complex, evaluating a DRWT design requires accurate predictive simulations, which incur high computational costs. Currently, there does not exist a design optimization framework for DRWTs. Since the design optimization of DRWTs requires numerous model evaluations, the purpose of this paper is to identify computationally efficient design approaches.Design/methodology/approachSeveral algorithms are compared for the design optimization of DRWTs. The algorithms vary widely in approaches and include a direct derivative-free method, as well as three surrogate-based optimization methods, two approximation-based approaches and one variable-fidelity approach with coarse discretization low-fidelity models.FindingsThe proposed variable-fidelity method required significantly lower computational cost than the derivative-free and approximation-based methods. Large computational savings come from using the time-consuming high-fidelity simulations sparingly and performing the majority of the design space search using the fast variable-fidelity models.Originality/valueDue the complex simulations and the large number of designable parameters, the design of DRWTs require the use of numerical optimization algorithms. This work presents a novel and efficient design optimization framework for DRWTs using computationally intensive simulations and variable-fidelity optimization techniques.

Improvement of the aerodynamic performance of vertical axis wind turbines with leading-edge serrations and helical blades using CFD and Taguchi method

The flow performance of vertical-axis wind turbines (VAWTs) is significantly deteriorated by dynamic stall at low tip-speed-ratios (TSR). Dynamic stall occurs periodically during the rotation of turbine blades and generates flow separations formed at leading-edges, which results in tremendous fluctuations in torque and essential reduction in power outputs. The target of this study is to apply a combination of CFD and Taguchi method to optimize the aerodynamic performance of a typical three-bladed VAWT at a low TSR of 2. Leading-edge wavy serrations and helical blade structures are implemented as the design parameters and the performance of these designs are compared with a corresponding baseline straight blade design of a traditional H-type VAWT. A comprehensive simulation study is carried out to obtain detailed flow characteristics. The Taguchi method is applied to find out the optimal combination of the selected factors such as amplitude and wave length of the serrations and twist angle of helical blade. A modified additive model is used to include the interaction effects among the selected factors. The optimal combination is found to appear in the case with an amplitude of 2.5%cb (cb is the blade chord length) and a wavelength of cb/6 for leading-edge serration as well as a blade twist angle of 60°. The simulation results show that the flow separations and torque fluctuations are significantly suppressed due to the passive flow control strategies implemented in the optimized VAWT model. The power output of the optimized wind turbine is found to increase by 18.3% in comparison to the baseline model. In addition, the force fluctuations are observed to be significantly reduced by employing the helical design, which is beneficial for improving the lifespan of turbines. The results derived from this study indicate a better VAWT design for the rural and built environments with relatively insufficient wind energy.

Optimal wind turbine allocation and network reconfiguration for enhancing resiliency of system after major faults caused by natural disaster considering uncertainty

This study proposes a two-stage stochastic optimisation model for jointly wind turbine (WT) allocation and network reconfiguration (NR) so as to increase the resiliency of distribution system in face of natural disasters. In this regard, in the first level, a possibilistic-scenario method is proposed to select the line outage scenarios. The proposed model is capable with distribution systems and considers different failure probabilities for system components subject to the intensity of natural disaster in its associated zone. After selecting the line outage scenarios, in the second level, a multi-stage optimisation framework is proposed for jointly NR and WT allocation in a multi-zone and multi-fault system, considering the uncertainty of system load and wind power generation. This strategy makes an interconnection between NR and islanded WTs to increase the resiliency of system and decreases the load shedding. Different economic objectives including, costs of load shedding and power generation are considered in the model. In addition, hardening budget is taken into consideration for the transmission lines, which is minimised during the optimisation process. The simulation results demonstrate the capability and necessity of proposed resiliency-oriented method and prove the importance of hardening budgets.

Analysis and optimization of ducted wind turbines

Wind-lens turbines offer the potential for better energy efficiency and better suitability for urban and suburban environments compared to unshrouded or bare wind turbines. Wind-lenses, which are typically comprised of a diffuser shroud equipped with a flange, can enhance the wind velocity at the rotor plane due to the generation of a lower back pressure. In this article, the wind-lens efficiency is increased by designing the shroud and turbine shape as well as flange height through an optimization process that seeks to maximize the power while minimizing drag and thrust forces. The employed optimizer is a multi-objective genetic algorithm (MOGA). Bezier curves are used to define the chord and twist distribution of the turbine blades and a piece-wise quadratic polynomial is utilized to define the shroud shape. The power, thrust, and drag coefficients are calculated by solving the Reynolds-averaged-Navier-Stokes (RANS) equations with the k−ε turbulence model for the flow within and around the diffuser augmented wind turbine using the open source code software OpenFOAM. To reduce the computational cost, the turbine rotor itself is modeled by incorporating blade element momentum model body forces into the RANS equations. Realistic rotor data for the sectional lift and drag coefficients for all angles of attacks are utilized via look-up tables. Grid convergence studies for verification and comparisons with experiments for validation are carried out to demonstrate that the adopted methodology is able to accurately predict the performance of a wind-lens prior to performing shape optimizations. It will be demonstrated that the resulting optimal designs yield significant improvements in the output power coefficient.

Wind Turbine Optimization for Minimum Cost of Energy in Low Wind Speed Areas Considering Blade Length and Hub Height

In recent years, sites with low annual average wind speeds have begun to be considered for the development of new wind farms. The majority of design methods for a wind turbine operating at low wind speed is to increase the blade length or hub height compared to a wind turbine operating in high wind speed sites. The cost of the rotor and the tower is a considerable portion of the overall wind turbine cost. This study investigates a method to trade-off the blade length and hub height during the wind turbine optimization at low wind speeds. A cost and scaling model is implemented to evaluate the cost of energy. The procedure optimizes the blades’ aero-structural performance considering blade length and the hub height simultaneously. The blade element momentum (BEM) code is used to evaluate blade aerodynamic performance and classical laminate theory (CLT) is applied to estimate the stiffness and mass per unit length of each blade section. The particle swarm optimization (PSO) algorithm is applied to determine the optimal wind turbine with the minimum cost of energy (COE). The results show that increasing rotor diameter is less efficient than increasing the hub height for a low wind speed turbine and the COE reduces 16.14% and 17.54% under two design schemes through the optimization.

Numerical Investigations of the Effects of the Rotating Shaft and Optimization of Urban Vertical Axis Wind Turbines

The central shaft is an important and indispensable part of a small scale urban vertical axis wind turbines (VAWTs). Normally, it is often operated at the same angular velocity as the wind turbine. The shedding vortices released by the rotating shaft have a negative effect on the blades passing the wake of the wind shaft. The objective of this study is to explore the influence of the wake of rotating shaft on the performance of the VAWT under different operational and physical parameters. The results show that when the ratio of the shaft diameter to the wind turbine diameter (α) is 9%, the power loss of the wind turbine in one revolution increases from 0% to 25% relative to that of no-shaft wind turbine (this is a numerical experiment for which the shaft of the VAWT is removed in order to study the interactions between the shaft and blade). When the downstream blades pass through the wake of the shaft, the pressure gradient of the suction side and pressure side is changed, and an adverse effect is also exerted on the lift generation in the blades. In addition, α = 5% is a critical value for the rotating shaft wind turbine (the lift-drag ratio trend of the shaft changes differently). In order to figure out the impacts of four factors; namely, tip speed ratios (TSRs), α, turbulence intensity (TI), and the relative surface roughness value (ks/ds) on the performance of a VAWT system, the Taguchi method is employed in this study. The influence strength order of these factors is featured by TSRs > ks/ds > α > TI. Furthermore, within the range we have analyzed in this study, the optimal power coefficient (Cp) occurred under the condition of TSR = 4, α = 5%, ks/ds = 1 × 10−2, and TI = 8%.

Overview of Wind Parameters Sensing Methods and Framework of a Novel MCSPV Recombination Sensing Method for Wind Turbines

The paper presents an overview of the traditional methods to obtain wind parameters such as wind speed, wind direction and air density. After analyzing wind turbines’ arrangements and communication characteristics and the correlation of operation data between wind turbines, the paper proposes a novel recombination-sensing method route of “measuring–correlating–sharing–predicting–verifying” (MCSPV) and explores its feasibility. The analysis undertaken in the paper shows that the wind speed and wind direction instrument fixed on the wind turbine nacelle is simple and economical. However, it performs in-process measurement, which restricts the control optimization of wind turbines. The light detection and ranging (LIDAR) technology which is accurate and fast, ensures an early and super short-time sensing of wind speed and wind direction but it is costly. The wind parameter predictive perception method can predict wind speed and wind power at multiple time scales statistically, but it has limited significance for the control of the action of wind turbines. None of the traditional wind parameter-sensing methods have ever succeeded in air density sensing. The MCSPV recombination sensing method is feasible, both theoretically and in engineering, for realizing the efficient and accurate sensing and obtaining of such parameters as wind speed, wind direction and air density aimed at the control of wind turbines.

A new evolutionary-analytical two-step optimization method for optimal wind turbine allocation considering maximum capacity

In this paper, a new two-step optimization algorithm is introduced for optimal placement of a Wind Turbine Generator (WTG) in a distribution network. The locations and the maximum capacities of WTGs, as well as their optimum power factor, are determined simultaneously in two different steps. In the first step, the locations and power factors of the WTGs are considered as solutions of a meta-heuristic optimization algorithm and in the next step, the optimal capacities of the WTGs are determined analytically. A recently introduced optimization algorithm known as the Lightning Attachment Procedure Optimization algorithm is employed for the first step, and a fast analytical method is used for the second one. The objective function of the optimization problem is considered for annual energy loss minimization. The proposed approach is applied on 85-bus test system, and the results are discussed. Fast convergence, best global answer finding, and robustness are the characteristics of the proposed method, which are concluded from the results and discussion.

Study on an innovative three-dimensional wind turbine wake model

In this paper, to help handle wind farm optimization problems, an original analytical three-dimensional wind turbine wake model is presented and validated. Compared with existing analytical wake models, the presented wake model also considers the wind variation in the height direction, which is more accurate and closer to the reality. The wake model is based on the flow flux conservation law, and it assumes that the wind deficit downstream of a wind turbine is Gaussian-shaped. The derivation process is described in detail. The wake model is validated by published wind tunnel measurement data at both horizontal and vertical sections. Detailed relative errors are analyzed: the relative errors are mostly within 5% in the horizontal profile validation and within 3% in the vertical profile validation. Based on the wake model, a series of prediction results from multiple views and at different positions are demonstrated. From the predictions, the three-dimensional wake model is effective in describing the spatial distribution of wind velocity. It makes a theoretical contribution to the single wake study, and it is also meaningful to the further study of multiple wakes. Because height is considered in the three-dimensional wake model, the model can be used to optimize wind turbine hub heights and to solve more wind farm layout optimization problems, which will further contribute to increasing the energy output and decreasing the cost of energy.

Determination of optimal wind turbine alignment into the wind and detection of alignment changes with SCADA data

Abstract. Upwind horizontal axis wind turbines need to be aligned with the main wind direction to maximize energy yield. Attempts have been made to improve the yaw alignment with advanced measurement equipment but most of these techniques introduce additional costs and rely on alignment tolerances with the rotor axis or the true north. Turbines that are well aligned after commissioning may suffer an alignment degradation during their operational lifetime. Such changes need to be detected as soon as possible to minimize power losses. The objective of this paper is to propose a three-step methodology to improve turbine alignment and detect changes during operational lifetime with standard nacelle metrology (met) mast instruments (here: two cup anemometer and one wind vane). In step one, a reference turbine and an external undisturbed reference wind signal, e.g., met mast or lidar are used to determine flow corrections for the nacelle wind direction instruments to obtain a turbine alignment with optimal power production. Secondly a nacelle wind speed correction enables the application of the previous step without additional external measurement equipment. Step three is a monitoring application and allows the detection of alignment changes on the wind direction measurement device by means of a flow equilibrium between the two anemometers behind the rotor. The three steps are demonstrated at two 2 MW turbines together with a ground-based lidar. A first-order multilinear regression model gives sufficient correction of the flow distortion behind the rotor for our purposes and two wind vane alignment changes are detected with an accuracy of ±1.4∘ within 3 days of operation after the change is introduced. We show that standard turbine equipment is able to align a turbine with sufficient accuracy and changes to its alignment can be detected in a reasonably short time, which helps to minimize power losses.