Three-bladed Wind Turbine Research Articles

Investigation on the Performance of Micro Wind Turbine Rotor Using Whale-Inspired Blade Based on Low Wind Regime

The potential of wind energy in a country varies depending on the region. For example, in Northern regions of Nigeria, cities like Minna, Sokoto, Kano and Jos are the most potential locations and experience not more than 5.24 m/s mean wind speed with Jos having the highest average wind speed. In most cases internationally wind turbines are design to operate at the rated wind speed much greater than mean wind speeds in Nigeria (in most cases above 8 m/s). Installation of these wind turbines in a similar location to Nigeria (in terms of wind speed condition) will significantly decrease their performance. Therefore, it become necessary to design and produce wind turbines that will function efficiently in low wind speed locations. One of the technologies to improve wind turbine rotor blade effectiveness in low wind regime is to boost the operating angle of the wind turbine, and hence the prospect for the improvement of wind turbine performance. An innovative way recognized previously by some researchers for increasing the working angle of the blade at low wind speed for improved performance is modification of wind turbine blade leading edge. This research studied three-bladed wind turbine rotor with modified blades leading edges (by incorporating sinusoidal bumps) at low wind speeds using CFD method. Two CAD models of wind turbine blades based on 0.8m three-bladed wind turbine rotor were modelled and simulated. One blade model is having straight leading edge (N-Blade) and the other having bumpy leading edge (M-Blade). Both models have NASA LS (1)-0413 cross-section profile. Simulations were run using ANSYS 20 from a velocity of 2 m/s to 10 m/s at the interval of 2m/s considering TSR of 6 and 8. At a TSR of 6, the coefficients of performance (Cp) values are not equal, with the straight blade having better performance than the bumpy blade at all velocities tested; the Cp values of blade with straight leading edge are 0.180, 0.267, 0.300, 0.313, 0.322 at respective velocities of 2, 4, 6, 8, and 10m/s, while Cp values of blade with bumpy leading edge at the same velocities are 0.165, 0.250, 0.281, 0.294, and 0.303 respectively. At a TSR of 8, the CP values closely match for both straight and bumpy blade at all velocities tested for. Simulations were further run at constant angular velocity of 120 rad/s for a TSR of 2, 4, and 10, where the peak performance occurs is around TSR of 6 and 8. For instance, the Cp values of M-Blade are 0.022, 0.173, 0.294, 0.313, and 0.116 respectively at the TSR of 2, 4, 6, 8, and 10. At TSR of 2, 4, 8 and 10, the performance of both airfoils closely matches except at a TSR of 6 where the N-Blade Cp value is 0.313 and is better than that of M-Blade Cp value (0.294). It shows that the blade leading edge modification could not have advantage at all flow conditions and size of the HAWT blades; it shows no advantage on the performance of the rotor blade tested in this research at the velocities at which the simulation was conducted.

Investigations of aerodynamics of three-bladed combined type wind turbine

The field of renewable energy utilized is expanding. For this reason, many researchers in this field have centered on investigating the utilization of sustainable energy and diminishing the utilization of fossil fuels. The VAWTs is one of the sorts of wind turbines that are right now broadly utilized. Utilizing the Darrieus wind turbine, its beginning torque value is little due to the little projected area in contact with the wind stream. To extend this beginning torque, the vane-type blade with a vertical axis of revolution has been installed, which contains movable vans and installed with a three straight- bladed Darrieus airfoil (NACA0012) on the same turning shaft. In this paper, the characteristic of a combined three–blade vane type and three-bladed Darrieus turbine was talked about computationally by utilizing CFD (Fluent) software’ with k-ω turbulence model and commercial accessible solid work 2016. Through present study, the results gotten demonstrate that the beginning torque of the combined wind turbine increases when the blades with even movable vans are installed with the straight -bladed Darrieus wind turbine. Expanding the starting torque of the combined turbine because the wind stream is freely passed without any resistance through the movable vanes that are completely open on the inverse side of the wind direction, leads to an increment within the output power of the turbine compared to the comes about confirmed within the published sources of the vertical axis wind turbine, which has different shapes.

Application of Intelligent and Digital Technologies to the Tasks of Wind Energy

The article considers the relevance and issues of wind turbine modeling, the principles of wind energy conversion (WEC) system operation, working areas and regulation. The influence of soft computing technologies on the different aspects of wind power systems, particularly in the fields of operation and maintenance, is considered. This article discusses the recent research, development and trends in soft computing techniques for wind-energy-conversion systems. For reliable analysis, the interaction of the wind-generator operation with the atmospheric boundary layer is considered. The authors give a detailed description of the approaches for the study and numerical modeling of the atmospheric boundary layer (ABL) in the vicinity of a wind farm. The study of the atmospheric boundary layer in the vicinity of the Ulyanovsk wind farm on the basis of cluster analysis of meteorological data is performed. Ten localizations of ABL homogeneous properties are identified. The subject of the study is the application of the results of cluster analysis to set linguistic variables in fuzzy inference algorithms as well as to adjust the initial conditions in the digital model of a wind generator. The results of cluster analysis made it possible to reasonably construct membership functions for the wind speed value in the fuzzy control algorithm to limit the output power of wind turbines. A simulation of the operation of a three-bladed horizontal type wind turbine for the conditions of one of the resulting clusters is performed, and the main regularities of the flow around the wind turbine are revealed. The results obtained are a valuable source for assessing the mutual influence of wind farms and the environment as well as wind farm site development.

Underactuated control and analysis of single blade installation using a jackup installation vessel and active tugger line force control

The assembly and installation costs account for a large share in the overall expenditures of an offshore wind farm project. Single blade installation is suitable for large scale wind turbines due to the lower crane capability requirement and lower transportation time. By introducing active tension control on the tugger lines, an automatic single blade installation approach can accomplish operations in higher sea states, reduce the waiting-on-weather time, and improve the operational efficiency. Compared to early research, a more complicated control objective is achieved in this paper, i.e., a two-tugger-line configuration is applied to stabilize the suspended blade in three degrees of freedom during crane rotation and blade root-hub mating processes. The pulleys on the crane boom, i.e., the ends of the tugger lines, are assumed to be fixedly placed, resulting in tugger line time-varying inclinations. A novel backstepping-like controller is designed and proved. It is able to stabilize the blade around its equilibrium and make it track the desired path. Sensitivity studies are conducted to evaluate the influence of the tugger line inclinations. In addition, the influence of the installed blades on a three-blade horizontal wind turbine with a monopile foundation is discussed. The proposed active control setup improves the installation success rate and reduces the risks for blade impacts that may occur during mating.

On wind turbine loading induced by non-uniform approaching flow at high Reynolds numbers

Influences of non-uniform incoming flow on the wind turbines blades forces and root bending moments (RBMs) are not fully understood. To advance our current understanding, numerical studies of a three-bladed horizontal axis wind turbine with cylinders placed in front of it to produce non-uniform flow approaching the turbine with different non-uniformity levels have been carried out to examine the variations of blade and rotor loading due to the non-uniform incoming flow. The phase-averaged predicted blade forces reveal that the blade tangential force, in-plane RBM, and power coefficient are much more sensitive to the upstream streamwise velocity variations and are much more strongly affected than the blade axial force, out-of-plane RBM, and thrust coefficient. It also shows that for non-uniform incoming flows the blade axial force to the blade tangential force ratio fluctuates significantly during one rotor revolution, resulting in large variations of the blade elastic torsion and that the total blade force (magnitude and direction) undergoes a non-linear change in the circumferential and radial directions, which will likely lead to the reduction in the turbine operational life significantly, especially for long lightweight blades of large size wind turbines. This study also shows different behaviors of the blade forces along the blade span under non-uniform upstream flows in terms of the amplitudes and standard deviations of their oscillations. For the blade tangential force, λ and σ increase monotonously along the blade span up to near the blade tip, whereas those of the blade axial force increase up to approximately 0.6 blade span and show an opposite trend behind that.

A Virtual Dual-Ripple Suppression Strategy of Double Fed Wind Turbine Under Wind Shear

Abstract With the increasing size and scale of wind turbines, the ripple caused by wind shear may have negative effects on wind turbines, such as decreasing grid-connected power quality and increasing mechanical loss. To address this issue, a virtual dual-ripple suppression strategy is proposed to suppress the ripple caused by wind shear without additional cost and sacrificing system efficiency. First, in this paper, a three-bladed double-fed wind turbine is taken as the research object with the analysis of its transmission mechanism and form of ripple. Second, an online artificial neural network (ANN) ripple detection method is proposed to detect the time-varying low-frequency ripple with high accuracy. In addition, a virtual dual-ripple suppression strategy composed of two ANN-based filters is utilized to suppress electromagnetic torque ripple and grid-connected power ripple simultaneously. Finally, the accuracy of the presented ANN ripple detection method and suppression strategy are verified by matlab simulation. The results show that the virtual dual-ripple suppression strategy can effectively suppress the transmission of ripple while increasing the conversion efficiency of wind energy without additional hardware circuits and equipment.

Wake Structure in Yawed Approaching Flows for an Axial-Flow Wind Turbine

Abstract Effects of yawed wind turbines on the wake structure are not fully understood. To obtain a better understanding, numerical studies of a small-scale three-bladed horizontal axis wind turbine at tip speed ratio (TSR) = 6.7 with yaw angles of zero, 15 deg, 30 deg, and 45 deg have been carried out to investigate the wake characteristics of the turbine in the near- and farwake. A hybrid approach coupling large eddy simulation (LES) with actuator line modeling (ALM) has been employed in the present study. The predicted results confirm the previous finding that the turbine wake is asymmetric under yawed approaching flows and the wake is inclined to the direction where the rotor is yawed. The present work further demonstrates that at high yaw angles the main wake may be divided into two smaller parallel wakes further downstream that are not symmetric suggesting a dependency on the turbine rotation direction. This study quantitatively explains how the nonuniform variations of radial velocity components at the turbine plane caused by the yawed flows result in the wake deflection and intersection of hub and blade tip vortices further downstream which leads to the wake splitting at high yaw angles.

Influence of Atmospheric Turbulence on Wind Turbine’s Rotor Teeter Dynamics

Wind energy is one of the fastest-growing sources of renewable energy. The mass and the cost of a wind turbine affect the cost of energy. A two-bladed wind turbine costs less than the most popular three-bladed wind turbine since it has one blade less. Although the less cost, the rotor dynamics of a two-bladed turbine limits its use. Due to the unbalanced loads of a two-bladed turbine, the rotor has an extra system for the rotor teeter. In this work, the rotor teeter dynamics are investigated under the influence of atmospheric turbulence. The AWT-27 two-bladed wind turbine is simulated for two different turbulence intensities of the values 10% and 50% turbulence at a mean wind speed of 12 m/s. The higher turbulence intensity indicates a 400% increase in the rotor mean teeter deflection. The rotor teeter mean velocity and acceleration increase as well by the ratios of 160% and 660% respectively. This massive increase in the teeter dynamics affects the fatigue loading of the rotor and hence reduces the lifetime of the wind turbine.

Flutter behavior of highly flexible blades for two- and three-bladed wind turbines

Abstract. With the progression of novel design, material, and manufacturing technologies, the wind energy industry has successfully produced larger and larger wind turbine rotor blades while driving down the levelized cost of energy (LCOE). Though the benefits of larger turbine blades are appealing, larger blades are prone to aeroelastic instabilities due to their long, slender, highly flexible nature, and this effect is accentuated as rotors further grow in size. In addition to the trend of larger rotors, non-traditional rotor concepts are emerging including two-bladed rotors and downwind configurations. In this work, we introduce a comprehensive evaluation of flutter behavior including classical flutter, edgewise vibration, and flutter mode characteristics for two-bladed, downwind rotors. Flutter speed trends and characteristics for a series of both two- and three-bladed rotors are analyzed and compared in order to illustrate the flutter behavior of two-bladed rotors relative to more well-known flutter characteristics of three-bladed rotors. In addition, we examine the important problem of blade design to mitigate flutter and present a solution to mitigate flutter in the structural design process. A study is carried out evaluating the effect of leading edge and trailing edge reinforcement on flutter speed and hence demonstrates the ability to increase the flutter speed and satisfy structural design requirements (such as fatigue) while maintaining or even reducing blade mass.

Life Cycle Assessment of Wind Turbine in Turkey

This article aims to assess life cycle analysis of a wind turbine in Turkey regarding production, transport, construction, operation, and disposal processes in terms of energy and environment. In this context, a 2-MW three-bladed horizontal axis wind turbine has been selected. Two different scenarios have been studied which comprises wind turbines using Al-Conductor and Cu-Conductor cables. Although the cost of Al-Conductor cables is low, their joule losses are higher. The life cycle assessment of a wind turbine includes production, transportation, construction, operation and disposal, and the energy has been generated in its operation time (selected as 20 years). Iron, cast iron, steel, copper, aluminum, and oil have been sent to a recycling facility and the composite materials has been sent for incineration at the end of its life. The energy payback period has been calculated as 10 months in both scenarios and the embodied energy is 2858.2 MWh and 2830.3 MWh for wind turbine using Al-Conductor and Cu-Conductor cable during its lifetime, respectively. Air emission and wastewater production have been calculated to assess environmental impacts (global warming, acidification, eutrophication, etc.) whose consequence provides an evaluation of the life cycle assessment of a wind turbine. For example, global warming is 14.44 and 15.24 g CO2 eq./kWh for wind turbine using Al-Conductor and Cu-Conductor cable, respectively. As a result, the life cycle analysis of the wind turbines has been evaluated and compared regarding two different scenarios according to the definition of ISO 14040 standard throughout its life from production to disposal.

Sustainability Assessment of Wind Farms

Sustainable energy solutions are becoming increasingly popular as the shift away from conventional fuel-based energy solutions continues. Solar, wind, and hydro solutions are the most frequently used renewable energy sources. Modern wind energy solutions are usually constructed using a design of a large three-bladed horizontal axis wind turbine (HAWT). The blades are upwind facing, which helps support the turbine tower against environmental strain and torque ripple produced from the spinning motion of the blades. HAWTs are usually organised into large groups referred to as wind farms. Wind farms are becoming increasingly popular with their ability to adapt to offshore and onshore environments. In both scenarios, wind turbines have a relatively low footprint, with the land underneath still available to be utilised for agricultural and aquacultural purposes. This paper investigates the sustainability of wind farms by surveying a range of papers. The papers will cover the development, construction, and continued operation of wind turbines providing insights into the sustainability issues. Reviewing these papers will allow for an informed revision to the code of sustainability for future implementations of wind farms. The paper concludes with a case study to apply the suggested sustainability code in a contextual scenario and recommendations for the general engineering profession.

The Wind Turbine Design and Test

Green energy harvester, known as wind turbine, able to convert mechanical works to electrical power. There are two main type of wind turbine that considered thoroughly, which are the horizontal and vertical axis wind turbine respectively. This project mainly focus on the design of new wind turbine that can operate well together in low wind speed condition in Malaysia. For the first stage of this project, the problems, purpose, and planning regarding with the project properly determined. Literature survey then furthered analyzed in order to know the wind power or behavior across the world, and specifically in Malaysia, research of turbine that can work in low wind speed condition, as well as parameter that often used in designing wind turbine by previous researcher. From the literature survey, the selected turbine was a Three-Bladed Savonius Wind Turbine, which is one type of Vertical Axis Wind Turbine (VAWT). That turbine will be attached to another VAWT turbine system to help generate more power and better performance. Design theoretical calculation and material selection have been properly analyzed before fabrication can be done. Upon completion of the fabrication, Savonius wind turbine section properly tested through experimental works by using simple wind tunnel in Faculty of Engineering Mechanical Workshop, and all readings and data collected using applicable tools and equipment. For the experimental works of Savonius rotor, the variable includes of blades curve angle from its center at different wind speeds. The data collected then interpreted through charts and graph for comparison and performance analysis, and conclude that 1200 blades curve angle from its center was the best among the other type of blades. From this project, it can be concluded that this type of mix wind turbine able to works in low wind speed condition in Malaysia, but a better improvisation and modification of the mix wind turbine will certainly improve its further performance and efficiency.

A Proper-Orthogonal-Decomposition (POD) Study of the Wake Characteristics behind a Wind Turbine Model

A comprehensive study was performed to analyze turbine wake characteristics by using a Proper-Orthogonal-Decomposition (POD) method to identify the dominant flow features from a comprehensive experimental database. The wake flow characteristics behind a typical three-bladed horizontal-axis wind turbine (HAWT) were measured in a large-scale wind tunnel with a scaled turbine model placed in a typical offshore Atmospheric Boundary Layer (ABL) wind under a neutral stability condition. A high-resolution Particle Image Velocimetry (PIV) system was used to achieve detailed flow field measurements to characterize the turbulent flows and wake vortex structures behind the turbine model. Statistically averaged measurements revealed the presence of the characteristic helical-tip vortex filament along with a unique secondary vortex filament emanating from 60% of the blade span measured from the hub. Both filaments breakup in the near-wake region (~0.6 rotor diameter downstream) to form shear layers, contrary to previous computational and experimental observations in which vortex filaments break up in the far wake. A Proper-Orthogonal-Decomposition (POD) analysis, based on both velocity and vorticity-based formulations, was used to extract the coherent flow structures, predominantly comprised of tip and midspan vortex elements. The reconstructions showed coherence in the flow field prior to the vortex breakup which subsequently degraded in the turbulent shear layer. The accuracy of the POD reconstructions was validated qualitatively by comparing the prediction results between the velocity and vorticity-based formulations as well as the phase-averaged PIV measurement results. This early vortex breakup was attributed to the reduced pitch between consecutive helical turns, the proximity between midspan filaments and blade tips as well as the turbulence intensity of the incoming boundary layer wind.

Optimal Design and Aerodynamic Performance Prediction of a Horizontal Axis Small-Scale Wind Turbine

The improved aerodynamic design of a horizontal axis small-scale wind turbine blade is crucial to increasing the efficiency and annual energy production of the turbine. One of the vital stages in aerodynamic design is the selection of the airfoil. Using the existing airfoils for a blade design which results in higher turbine characteristics is tedious. Consequently, this paper provides an optimal design strategy for a horizontal axis small-scale wind turbine blade through the multiobjective optimization of the airfoil using the Nondominated Sorting Genetic Algorithm II (NSGA-II). The latter outperforms the other commonly used genetic algorithms (GAs), as well as the Computational Fluid Dynamics (CFD) investigation of the different airfoil types and the wind turbine rotors on the steady or unsteady state aerodynamic performance. An NACA4412 airfoil with higher aerodynamic efficiency is considered as a baseline for the optimization in order to increase the lift coefficient and lift to drag ratio while avoiding excessive variations in the maximum relative thickness and area. The optimized airfoil (NACA4412-OPT) is used as the cross-sectional profile in the design procedure for a novel 1.15 m diameter three-bladed wind turbine rotor at a wind speed of 11.5 m/s, tip speed ratio of 4.65, and pitch angle of 0.2° by the Wilson design method. The two-dimensional analysis demonstrates that the optimized airfoil outperforms the other airfoils yielding the highest lift coefficient and lift to drag ratio, as well as a larger pitch range. The three-dimensional analysis shows that the time-averaged power coefficient value (0.33) of the new wind turbine is almost 26% higher and more stable than that of the original wind turbine while avoiding a high increase of the axial thrust.

Dynamic Investigations between Two- and Three-bladed Wind Turbines with Various Yaw, Tilt and Cone Angles

Tilt and cone are included in wind turbine design to increase tower clearance. Yaw misalignments take place often during turbine operation. The combined effects of these parameters modify the relative wind speed experienced by wind turbine blades, thereby altering the turbine’s dynamics. Consequently, power and loads, key design considerations, are affected. In the absence of exhaustive research available on this topic, this paper provides a quantitative analysis on the impact of tilt, cone and yaw on power and loads. The DTU 10MW Reference Wind Turbine and its two-bladed equivalent are evaluated. The results are obtained using the aeroelastic code HAWC2. It is demonstrated that the ultimate and fatigue loads are greater in the two-bladed than in the three-bladed model during operations. Tilt, cone and ±10º yaw reduce the annual energy production by up to 1%. These three parameters generally increase ultimate and fatigue loads. However, the relationship between these parameters and their impact on the bending moments of both wind turbines is complex, and the results are configuration dependent. It is concluded that the combination of these three parameters must be included as part of the design load examination of any target wind turbine.

Effect of tip speed ratio on the aerodynamic noise of a small wind turbine: An optimization study

A dual-objective optimization study was carried out to illuminate how the tip speed ratio of a small wind turbine affects the aerodynamic noise as well as the blade geometry. A 0.75 kW three-bladed small horizontal axis wind turbine was selected as the case study. Two important goals were considered in the study: maximization of the output power and the minimization of the aerodynamic noise. The former was calculated by the well-known blade-element momentum theory while a validated semi-empirical model was adopted for the computation of the latter. A combination of these goals defined the objective function and the weighted-sum approach was employed to find the optimal values for the design variables of the optimization including the distributions of the chord and the twist angle along the blade together with the tip speed ratio. The extracted power was calculated at the rated wind speed of 10 m/s while the noise was computed at lower wind speeds of 5 and 7.5 m/s. The genetic algorithm technique was adopted for the muti-objective optimization. The results revealed the importance of the blade tip region in producing the emitted aerodynamic noise. Specifically, an increase in the chord and twist values near the tip results in the reduction in the emitted noise. Results also show that a good compromise between the two goals is achievable such that a noticeable reduction in the emitted aerodynamic noise is attainable in exchange for a very small drop in the power coefficient. The optimization results also indicated that the noise could be adequately reduced at the smaller value of the tip speed ratio without a large reduction in output power which is due to the decrease in the rotational speed of the turbine.

Rotational and blockage effects on a wind turbine model based on local blade forces

This paper describes the results of an extended experimental campaign, reporting surface pressure measurement over one of the blades of the Berlin Research Turbine (BeRT), placed in a closed-loop wind tunnel facility. BeRT is a three-bladed horizontal axis wind turbine with a 3m rotor diameter. The focus is, on the one side, on the three-dimensional effects experienced by the rotating blade, in comparison to 2D approaches by means of XFoil simulations and 2D blade section experiments. On the other side, the blockage effects are investigated between the wind turbine model, placed in the wind tunnel where a 40% blockage ratio is produced, and lifting line free vortex wake simulations, where wind tunnel walls are not considered. Additionally, CFD computations are added in the comparison, with simulations of the far-field and with the wind tunnel walls. The turbine model is studied at several operational conditions such as different blade pitch angles and turbine yaw misalignments. Results are presented in terms of local force components derived from the surface pressure measurements. It is shown that rotational augmentation is evident at the blade mid-span location despite the large blockage. Additionally, the blockage is noticed by means of an offset in both normal and tangential local forces conserving trends and features under axial inflow and yaw misalignments. It is found that the offset in forces can be counteracted by pitching the blades.

Effect of Yaw Angle on Large Scale Three-blade Horizontal Axis Wind Turbines

Offshore Horizontal Axis Wind Turbines (HAWT) are used globally as a source of clean and renewable energy. Turbine efficiency can be improved by optimizing the geometry of the turbine blades. Turbines are generally designed in a way that its orientation is adjustable to ensure the wind direction is aligned with the axis of the turbine shaft. The deflection angle from this position is defined as yaw angle of the turbine. Understanding the effects of the yaw angle on the wind turbine performance is important for the turbine safety and performance analysis. In this study, performance of a yawed HAWT is studied by computational fluid dynamics. The wind flow around the turbine is simulated by solving the Reynolds-Averaged Navier-Stokes equations using software ANSYS Fluent. The principal aim of this study is to quantify the yaw angle on the efficiency of the turbine and to check the accuracy of existing empirical formula. A three-bladed 100-m diameter prototype HAWT was analysed through comprehensive Computational Fluid Dynamics (CFD) simulations. The turbine efficiency reaches its maximum value of 33.9% at 0° yaw angle and decreases with the increase of yaw angle. It was proved that the cosine law can estimate the turbine efficiency with a yaw angle with an error less 10% when the yaw angle is between –30° and 30°. The relative error of the cosine law increase at larger yaw angles because of the power is reduced significantly.

Modelling and Control of a Small Domestic Wind Turbine

A wind turbine is a machine that converts the kinetic energy of wind into mechanical energy like wind turbines. This mechanical wind power has been used through the ages to pump water or grind grain. Current machines are used to produce wind-type electricity which is consumed locally (isolated sites), or injected into the electricity network (wind turbines connected to the network). In this work, we are only interested in the modelling of a three-bladed horizontal axis wind turbine. All the models were developed by the Matlab/Simulink software, which makes it possible to set up fairly quickly models as well as the associated. The results revealed that the wind profile ranges between 6-7 (m/s), the power coefficient Cp for a pitch angle of =2 has an average value of 0.54 with a relative speed λ value of 6.40, and when the origin of electrical losses is ignored, the electrical power equals the electromagnetic power, and the mechanical speed is stable between (70-80 rd/s).

Validation of a Large-Eddy Simulation Approach for Prediction of the Ground Roughness Influence on Wind Turbine Wakes

The ability of high-fidelity computational fluid mechanics simulation to quantitatively predict the influence of ground roughness on the evolution of the wake of a three-bladed horizontal axis wind turbine model is tested by comparison with wind tunnel measurements. The approach consists of the implicit approximate deconvolution large-eddy simulation formulation of Hickel et al., (2006), that is, for the first time, combined with a wall-stress model for flow over rough surfaces and with the actuator line approach (ALM) for modeling of the rotor. A recycling technique is used for the generation of turbulent inflow that matches shear exponents α=0.16 (medium roughness) and α=0.32 (high roughness) and turbulence level of the reference experiments at hub height. Satisfactory agreement of the spectral content in simulation and experiment is achieved for a grid resolution of 27 cells per rotor radius. Except for minor differences due to neglecting nacelle and tower in the simulation the LES reproduces the shapes of mean flow and Reynolds stress profiles in the wake. The deviations between measurement and simulation are more prominent in a vertical cut plane through the rotor center than in a horizontal cut plane. Simulation and experiment deviate with respect to the roughness influence on the development of the wake width; however, the relative change of the maximum wake deficit and of the vertical wake center position due to changes in ground roughness is reproduced very well.