Power Performance Of Wind Turbines Research Articles

Power performance and self-starting features of H-rotor and helical vertical axis wind turbines with different airfoils in turbulence

Wind tunnel tests were conducted to systematically assess the aerodynamic performance of both H-rotor and helical vertical axis wind turbines (VAWTs) in smooth and turbulent flows. The effects of airfoil section and pitch angle β on the power and self-starting performance were examined for both types of turbines. The helical turbine had a wider operating range of tip speed ratios (TSR λ) and much lower power performance than its H-rotor counterpart. This phenomenon was attributed to the flow deflection of helical blades due to their three-dimensional features, as well as that dynamic stall of a helical blade would not occur simultaneously for all blade elements. The helical turbine did not exhibit notably improved self-starting performance despite of the high manufacturing cost. Moreover, the start-up process was analyzed by using the static torque coefficient CT of both single-bladed and three-bladed turbines. It was found that turbulence intensity exercised a significant impact on CT. Turbulence would cause serious fatigue issues for H-rotor turbines and change the driving mechanism of helical turbines though it enhanced the self-starting performance. Recommendations were finally provided for the design of VAWTs in built environments.

Power Performance of Starting-Improved and Multi-Bladed Horizontal-Axis Small Wind Turbines

Power Performance of Starting-Improved and Multi-Bladed Horizontal-Axis Small Wind Turbines

Power performance enhancement of vertical axis wind turbines by a novel gurney flap design

PurposeNowadays flaps and winglets are one of the main mechanisms to increase airfoil efficiency. This study aims to investigate the power performance of vertical axis wind turbines (VAWT) that are equipped with diverse gurney flaps. This study could play a crucial role in the design of the VAWT in the future.Design/methodology/approachIn this paper, the two-dimensional computational fluid dynamics simulation is used. The second-order finite volume method is used for the discretization of the governing equations.FindingsThe results show that the gurney flap enhances the power coefficient at the low range of tip speed ratio (TSR). When an angled and standard gurney flap case has the same aerodynamic performance, an angled gurney flap case has a lower hinge moment on the junction of airfoil and gurney flap which shows the structural excellence of this case. In all gurney flap cases, the power coefficient increases by an average of 20% at the TSR range of 0.6 to 1.8. The gurney flap cases do not perform well at the high TSR range and the results show a lower amount of power coefficient compare to the clean airfoil.Originality/valueThe angled gurney flap which has the structural advantage and is deployed to the pressure side of the airfoil improves the efficiency of VAWT at the low and medium range of TSR. This study recommends using a controllable gurney flap which could be deployed at a certain amount of TSR.

Wind tunnel experiment on the influence of array configuration on the power performance of vertical axis wind turbines

Because of the development of wind energy technology, the power coefficient of a wind turbine is close to its theoretical limit. The conversion rate of wind energy that humans can extract from a given wind farm, however, is far from ideal. Increasing the power density by optimizing the arrangement of wind turbines has been a popular field of research in recent years. In the present work, a systematic study on the influence of array configuration on the power performance of vertical axis wind turbines is performed through wind tunnel experiments. Multiple transversal and longitudinal layouts are tested, and both the relative position and rotational direction are considered. The optimal mode of the transversal layout is counterforward rotation, and the maximum power coefficient of the turbine pair is 8.2% higher than that of an isolated turbine when the transverse spacing is 2.4 rotor diameters. The maximum power coefficient of a downstream turbine is found to be increased by 45% and 61.1% with respect to an isolated turbine in the two-turbine and three-turbine longitudinal layouts, respectively. Triangular and truss layouts are proposed based on the prevailing wind direction. The results of the experiment confirmed that further improvement of the average power coefficient can be obtained by optimizing the array configuration of the turbines.

Effect of airfoil shape on power performance of vertical axis wind turbines in dynamic stall: Symmetric Airfoils

The current design of vertical axis wind turbines (VAWTs) suffers from inevitable change in tip speed ratio, λ, in variant wind conditions due to fixed rotor speed. At relatively high wind speeds, which are promising due to high wind power potential, VAWTs operate at low λ with poor power coefficient. Morphing airfoils can be a potential solution by modifying the airfoil shape to optimal at each λ. The optimal airfoil shape for VAWTs at low λ, where dynamic stall is present, has not yet been studied in the literature, therefore, the present study addresses this gap by focusing on this regime to serve as a step towards designing morphing airfoils for VAWTs by identifying the optimal airfoil shape at low λ. The present study performs a combined analysis of three shape defining parameters, namely the airfoil maximum thickness and its position as well as the leading-edge radius, to reveal the overall design space. The analysis is based on 252 high-fidelity transient CFD simulations of 126 identical airfoil shapes. The simulations are verified and validated with three experiments. The results show that the three shape defining parameters have a fully coupled impact on the turbine power and thrust coefficients. When λ reduces from 3.0 to 2.5, the optimal airfoil changes from NACA0018–4.5/2.75 to NACA0024–4.5/3.5, that is increasing the maximum thickness from 18%c to 24%c and shifting its position from 27.5%c to 35%c, while the leading-edge radius index, I, remains 4.5. In general, reducing I from the default value of 6.0 to 4.5 is found to increase the turbine CP.

Design and Verification of the LQR Controller Based on Fuzzy Logic for Large Wind Turbine

In this study, a linear quadratic regulator based on the fuzzy logic (LQRF) control algorithm for a variable-speed variable-pitch wind turbine was designed. In addition, to verify the optimum performance of the controller, simulations and wind tunnel tests were conducted. In the simulation, the performances of the proportional-integral (PI) and LQRF algorithms were compared in the transition region and the rated power region. In the wind tunnel test, the applicability of the LQRF algorithm was verified by comparing it with the conventional PI algorithms. The results showed that when compared with the PI control, the proposed LQRF control reduced the tower vibration by up to 12.50% depending on the operating region. Furthermore, the power deviation was reduced by 38.93%. These tests confirmed that the proposed LQRF control increases the power performance and structural stability of wind turbines compared with conventional PI controls.

An experimental investigation into performance characteristics of H-shaped and Savonius-type VAWT rotors

The effects of flow regime and rotor configuration strongly influence the power performance of vertical axis wind turbines (VAWTs). Yet, there exits few experimental investigations from literature that have been carried to explain this effect. This could be attributable to huge wind tunneling cost requirement and an array of design skills required including time constrains. The balance between cost and power performance has limited development of VAWTs towards utility scale type. In this paper therefore, we seek to investigate in detail the performance characteristics of vertical axis wind rotors in a wind tunnel environment. The H-Darrieus and Savonius-type VAWT configurations have been utilized to carry out the investigation. A systematic analysis of effect of blade number, rotor configuration, and flow regime including comparison of the two configurations was presented to predict the power performance using a rotary sensor. Results revealed a significant impact of flow field regime on power performance of the VAWT models, with the Savonius-type rotor attaining lower power coefficient (CP) than the Darrieus-type rotor across all the tested wind speeds. In addition, increase in number of blades for Darrieus-type rotor revealed narrower negative CP band that decreased with increase in wind speeds. In both configurations, the CP decreased at low tip speed ratios while an increase in CP was revealed at high tip speed ratios. The understanding gained from the results could be useful to the VAWT research community, and the findings can be extended to the design of wind turbines for mini-grid and utility scale applications.

Changes in wind turbine power characteristics and annual energy production due to atmospheric stability, turbulence intensity, and wind shear

The power generation of wind turbines varies depending on external environmental conditions. To present universal correlations between conditions that affect wind speed and wind turbine power, this study analyzed the effects of three atmospheric factors—atmospheric stability, turbulence intensity (TI), and wind shear exponent (WSE)—on the power performance and annual energy production (AEP) of wind turbines. Additionally, the horizontal and vertical speed components of the 3D sonic anemometer were investigated. At two measurement heights, unstable regimes showed an ascending air current, whereas stable regimes simultaneously showed both ascending and descending currents. Power curves calculated for each atmospheric factor regime revealed that atmospheric stability (200 kW–11 m/s) exhibited the greatest difference, followed by TI (91 kW–11 m/s) and WSE (32 kW–10.5 m/s). Finally, AEP was calculated at the annual mean wind speed of the study site and exhibited variations of 1.4–4% according to the factor regime. The AEP difference due to the change in atmospheric stability was greatest, and AEP was highest in moderately unstable atmospheric conditions. Clearer understanding of the effects of atmospheric factors on the power characteristics and AEP of wind turbines is expected to deliver practical benefits for wind-resource assessment and power-production prediction.

Performance and Aeroacoustic Noise Prediction for an Array of Small-Scale Vertical Axis Wind Turbines

Small-scale vertical axis wind turbines are good candidates for urban area use where, due to various obstacles, the airflow is turbulent. In urban areas, air velocity is mostly low and site specific, so just in a few places, like tall buildings, there are suitable airflow situation in order to use turbine, so it is a good idea to install more than one turbine in such locations. On the other hand, acoustic noise that is emitted from turbines may bother people living in that area. In the current study, power performance of small-scale vertical axis wind turbines in a V-form array configuration is investigated using detached eddy simulation method. Also, Ffowcs Williams and Hawkings acoustic analogy formulation is conducted in order to predict the noise radiation level of turbines. Results showed that power performance of most of the turbines increased due to venturi effect that is made by low speed regions behind turbines. Acoustic noise analysis showed that there is a strong enhancement in sound pressure level in receivers compared with the isolated turbine.

Structure Analysis of an Innovative Vertical Axis Wind Turbine with Inclined Pitch Axes using Finite Element Method

Pitch regulation is critical to power performance of wind turbines. However, the complexity of the conventional pitch system of vertical axis wind turbines (VAWTs) retards its appliance. In the present study, an innovative pitch system of a VAWT with inclined pitch axes was proposed where a slider in the main shaft actuated upwards or downwards drives blades to be folded by linkage mechanisms. Effect of design parameters of the pitch system on blade folding movement control sensitivity was evaluated. Loads of pitch hinge, deformation of blades and stresses of components were analyzed as well as natural frequencies of the wind turbine with various azimuth and fold angles under rated operational conditions by finite element method and effect of design parameters on structural performance of the wind turbine was investigated. It was found that deformation of blades and stresses of supporting arms deteriorated but natural frequencies of the wind turbine increased when blades were folded in the negative direction. In addition, the increasing arm interval height improved structural performance with the increasing natural frequencies. In the contrary, the decreasing blade linkage length, shaft linkage length and slider height improved structural performance with the decreasing natural frequencies. This study laid the foundation for the further design optimization of the novel pitch system.

Assessment and optimization of the power performance of twin vertical axis wind turbines via numerical simulations

The power performance of twin vertical axis wind turbines (VAWTs) is believed to surpass that of their individual counterparts. In this study, the power performance of twin VAWTs was investigated via computational fluid dynamics (CFD) simulations by changing their configuration parameters, including the airfoil section (NACA), solidity ratio (σ), pitch angle (β), rotational direction (φ), and turbine spacing (S/D). The CFD model was validated against wind tunnel test data from the literature. An L16 (45) orthogonal table was adopted to optimize the power performance using the Taguchi method. The rated power coefficient (CP) and rated tip speed ratio (TSR) were calculated for the 16 cases in the table. The extent of impact of the five parameters on the rated TSR ranked as σ ˃ β ˃ NACA ˃ φ ˃ S/D. In comparison, the extent of impact of these parameters on CP ranked as β ˃ S/D ˃ σ ˃ NACA ˃ φ. The optimal and worst configurations of the twin VAWTs were determined and their CP values increased by 13% and 8%, respectively, from that of their standalone counterparts. Moreover, the rated TSRs of the twin VAWTs differed from those of their standalone counterparts.

Effects of instantaneous tangential velocity on the aerodynamic performance of an H-Darrieus wind turbine

Recently, small scale H-Darrieus vertical axis wind turbines (VAWTs) have got great attention of researchers and wind turbine manufacturers due to their application at roof-tops of residential buildings. They are generally preferred over horizontal axis wind turbines (HAWTs) in terms of lower levels of noise production, operation at low wind speeds and lower manufacturing costs. But the main problem with such wind turbines is their low efficiency, which is mainly due to the complex flow around the turbine blades. It is of great importance to first fully understand the nature of complex aerodynamics associated with such wind turbines. Present study analyzes the instantaneous tangential velocity (ITV) and its impact on the power performance of H-Darrieus wind turbine at five different tip speed ratios (TSRs) i.e. 1–5. Computational models based on large eddy simulations (LES) have been developed using commercial software SC/Tetra V12. Throughout the numerical simulation, it is found that ITV of single blade has a negative value (reverse rotation) for TSRs 1–3 when the azimuth position ranges from 80° to 140°, whereas it has positive values during the remainder of the rotation for the mentioned TSRs. Furthermore, the magnitude of the negative ITV for a single blade was found to increase from TSR 1 to 3; the maximum value of the negative peak is equal to approximately −17.2 m/s while at the azimuth position of 110° for blade number 1 at TSR 3. On the other hand, no negative value of ITV is found for any of the three blades during a complete rotation at relatively higher values of TSRs i.e. 4 and 5. The possible physical reasons behind this behavior have been explained through aerodynamic forces and 2D color contours of important parameters, such as vorticity and static pressure. Finally, a discussion has been included in the final section of this paper explaining how negative ITV affects the power performance of H-Darrieus wind turbines. The current CFD model has been compared and validated with experimental data.

Validation of FAST.Farm Against Large-Eddy Simulations

FAST.Farm is a new midfidelity, multiphysics engineering tool for modeling the power performance and structural loads of wind turbines within a wind farm, including wake and array effects. Previous calibration of the tuneable model parameters of FAST.Farm has shown that its prediction of wake dynamics for a single wind turbine across different atmospheric stability conditions and nacelle-yaw errors matches well with high-fidelity large-eddy simulation at a small fraction of the computational expense. This paper presents a validation of FAST.Farm against large-eddy simulation for a series of cases—independent from those used to support the calibration—considering single-turbine and small wind-farm scenarios, which are both subject to variations in inflow and control. The validation has demonstrated that FAST.Farm reasonably accurately predicts: (1) thrust and power for individual turbines both in isolation and down the row of the small wind farm, (2) wake meandering behavior across different atmospheric conditions, and (3) averaged wake-deficit advection, evolution, and merging effects. The validation also highlights potential physics that could be improved in FAST.Farm in the future.

Assessment of solidity effect on the power performance of H-rotor vertical axis wind turbines in turbulent flows

Recent research suggests that vertical axis wind turbines (VAWTs) are suitable for urban installations. Nevertheless, systematic investigation of the power performance of VAWTs operating in flows of various turbulence levels remains limited. This study presents the influence of solidity on the aerodynamic performance of H-rotor VAWTs immersed in turbulence via wind tunnel tests. Homogeneous turbulence of various levels was generated by a wooden grid. A turbine control system was used to tune the blade speed ratio (BSR) and measure the rotational speed and torque. The relationship between the turbine's power coefficient, CP, and BSR, λ, was examined at different turbulence levels, I. Further, the impact of changes in the solidity ratio, σ, on the CP–λ curve was investigated. The analysis results show that the CP value of the turbine in turbulent flows was, on average, two times that of the one in smooth flow. However, a simple relationship between the increase in turbulence intensity and the increase in power performance of the wind turbine cannot be concluded. It was also observed that the turbine with a higher solidity obtained a larger rated CP, irrespective of flow regimes. Moreover, the turbine with a medium solidity ratio, σ = 0.45, was able to produce power over a broader range of BSRs than the one with low/high solidity in turbulent flows.

Study of ice accretion feature and power characteristics of wind turbines at natural icing environment

Wide cold regions with high air density as well as wind speed are much beneficial for the wind energy exploitation. However, wind turbines in these regions always suffer a series of icing issues, especially the blade aerodynamics degradation and much production loss in winter. Therefore, the paper aims to study the ice accretion feature on blades and the effect of ice severity on the power performance of wind turbines at natural icing environment. The ice distribution on the blade is analyzed quantitatively in the image processing method, and it is found that the ice thickness on the blade increases rapidly from the root to the middle of the blade, and then slowly from the middle to the blade tip. In the icing duration period, both the pitch angle and rotor speed of the wind turbine fall remarkably at the same wind speed, and the pitch angle shows more sensitive to the blade icing for wind turbines with the traditional control strategy. Based on the statistical operating data of the 300 kW wind turbine in different icing cases, the rotor performance deteriorates more seriously as the ice thickness of the blade increases, which changes the original matching relation between the rotor and generator. In addition, the ice thickness of the leading edge at r/R = 0.95 shows great correlation with power loss in given icing cases, and this correlation still needs to be studied further at more icing events. The results can provide a reference for the operation performance of wind turbines in cold regions.

Formula for estimating the uncertainty of manufacturer's power curve in pitch‐controlled wind turbines

This study proposes a new formula for estimating the uncertainty in pitch-controlled wind turbines regardless of the type of wind turbines or the availability of measurement data. The results obtained using a manufacturer's power curve (MPC), which is defined as the representative value of the power performance of wind turbines, may differ from the prediction results of power generation obtained using an actual power curve measured at a real wind farm. Therefore, the uncertainty of the MPC can considerably influence the calculation of power generation. However, the current methods used for uncertainty calculation either use a random constant chosen by the judgment of individual analyzers based on their experience or rely on a limited set of empirical formulas suggested through the analysis of data measured from specific wind turbines. To solve this problem, we suggest a new formula for uncertainty estimation that has general applicability. The suggested formula was validated by comparing its results with the data output measured from a real wind farm. In addition, a comparison of the real-time estimation results of wind power generation and measurement results demonstrates that the proposed formula produces more reliable results than the existing formula.

Design & optimization of a small wind turbine blade for operation at low wind speed

A small wind turbine blade was designed and optimized in this research paper. The blade plays an important role, because it is the most important part of the energy absorption system. Consequently, the blade has to be designed carefully to enable to absorb energy with its greatest efficiency. The main objective of this paper is to optimized blade number and selection of tip speed ratio corresponding to the solidity. The power performance of small horizontal axis wind turbines was simulated in detail using blade element momentum methods (BEM). In this paper for wind blade design various factors such as tip loss, hub loss, drag coefficient, and wake were considered. The design process includes the selection of the wind turbine type and the determination of the blade airfoil, twist angle distribution along the radius, and chord length distribution along the radius. A parametric study that will determine if the optimized values of blade twist angle and chord length create the most efficient blade geometry. The 3-bladed, 5-bladed and 7-bladed rotor achieved maximum values of Cp 0.46, 0.5 and 0.48 at the tip speed ratio 7, 5 and 4 respectively. It was observed that using BEM theory, maximum Cp varied with strongly solidity and weakly with the blade number. The studies showed that the power coefficient increases upto blade number B = 5, while the blade number if increased above 5 then the power coefficient decreases at operating pitch angle equal to 3°. Highest Cp would have solidity between 4% to 6% for number of blade 3 and design point tip speed ratio of about "7". Highest Cp would have solidity ranging from 5% to 10% for number of blade 5 and 7 and design point tip speed ratio of about 5 and 4 respectively.

Aerodynamics performance of continuously variable speed horizontal axis wind turbine with optimal blades

For conventional HAWT (horizontal axis wind turbines), the rotor speed is maintained constant while the blade tip speed changes continuously. This reduces considerably the power performance of the wind turbine particularly at high wind speeds where the tip speed ratio is small. With growth of variable speed generators, a compact BEM (blade element momentum) analysis is derived to design optimal blades for continuously variable speed HAWTs. First, a generalized quadratic equation on the angular induction factor is introduced which is related to local axial induction factor, blade local speed ratio, and drag to lift ratio. Second, the optimal blade geometry is obtained for which the maximum power coefficient is calculated at different design tip speed ratios and drag to lift ratios by assuming variable operational speed. Third, it is demonstrated that the power performance of the variable speed wind turbine is significantly higher than the conventional constant speed wind turbines. In addition, the present BEM modeling may be useful to reduce the computational effort of iterative numerical methods used in determining off-design power performance of conventional wind turbines with constant speed.

Phases of icing on wind turbine blades characterized by ice accumulation

Icing experiments on wind turbine blade profiles have been performed at the University of Manitoba Icing Tunnel Facility to facilitate a greater understanding of the mechanisms involved in the icing process for wind turbines exposed to cold climates. Blade icing results in the degradation of power performance and is a critical issue for the optimization of power performance and safe operation of wind turbines. Accumulation rate, the amount of ice that accumulates at the leading edge of the blade profile as a function of time, provides a characteristic measurement that can be used to classify the phases of icing in an icing event and further identify the severity of potential problems arising as a result of ice accumulation on wind turbine blades. To control this characteristic, the mitigation strategies that were employed involved coatings, heat treatments and the combination thereof, in both glaze and rime icing regimes. By understanding the icing process and its characteristic behavior to non-mitigated and mitigated scenarios, the phases of icing of both circumstances may be defined. This paper documents the data recorded from the experimental icing event and provides results of the comparative behavior of the icing mitigation strategies and extends this understanding to define the phases of icing on wind turbine blades.

Power Curve Characterization I: Improving the Bin Method

Neural network approaches have been used to try and characterise the power performance of wind turbines in a wind farm. Stochastic techniques are often dismissed as being inferior to those which use neural networks but those stochastic techniques proposed are often overly simplistic. We propose modifications to the IEC 61400-12 bin method in order to provide a more accurate characterisation of wind turbine performance in complex terrain taking account of direction and using a varying power law dependence of power output on wind speed. The method is validated using data from a real wind farm.