Wind Turbine Airfoil Performance Optimization Using the Vortex Lattice Method and a Genetic Algorithm

The roughness increase on horizontal axis wind turbine (HAWT) blade surface, especially on the leading edge, can lead to an aerodynamic performance degradation of blade and power output loss of HAWT, so roughness sensitivity is an important factor for the HAWT blade design. However, there is no criterion for evaluating roughness sensitivity of blade currently. In this paper, the performance influences of airfoil aerodynamic parameters were analyzed by the blade element momentum (BEM) method and 1.5 MW wind turbine blade. It showed that airfoil lift coefficient was the key parameter to the power output and axial thrust of HAWT. Moreover, the evaluation indicators of roughness sensitivity for the different spanwise airfoils of the pitch-regulated HAWT blade were proposed. Those respectively were the lift-to-drag ratio and lift coefficient without feedback system, the maximum lift-to-drag ratio and design lift coefficient with feedback system for the airfoils at outboard section of blade, and lift coefficient without feedback, maximum lift coefficient with feedback for the airfoils at other sections under the pitch-fixed and variable-speed operation. It is not necessary to consider the roughness when HWAT can be regulated to the rated power output by the pitch-regulated and invariable-speed operation.

<div class="section abstract"><div class="htmlview paragraph">Wind energy is clean and renewable source of energy that is an attractive alternative to non-conventional sources of energy. Due to rapid increase in global energy requirements, this form of energy is gaining its share of importance. Unlike nuclear power or tar sand oils, wind energy does not leave a long-term toxic legacy. Using MATLAB algorithms, multi-optimization of wind turbine design can be achieved. Therefore, an aerodynamic mathematical model is developed to obtain the optimal chord length and twist angle distribution along the blade span. Further, a promising generic blade design is used to initialize a detailed structure optimization wherein leading edge panel (LEP), Spar cap, Shear web, Trailing edge panel (TEP) reinforcement are sized using composite laminates so that the blade is according to the intended design standard. Initially blade airfoils are analyzed on 2D platform and then the results are used to construct 3D model of Horizontal Axis Wind Turbine (HAWT) blade. The 3D designing of composite HAWT blade is done by CAD software Solidworks v16.0 through different airfoil for root, primary and tip and optimization of material thickness and overall mass reduction by the use of composite material through optimization of skin thickness of wind turbine is achieved. This paper is focused on the importance of structural design for optimization of HAWT blade. On further analysis, an increase in aerodynamic power generation as well as marked improvements in overall blade deformation and tip deflection characteristics is observed.</div></div>

Elastic actuator line modelling for wake-induced fatigue analysis of horizontal axis wind turbine blade

Wind turbine blades are the most critical components of wind turbines. Full-scale blade fatigue testing is required to verify that the blades possess the strength and service life specified in the design. Unfortunately, the test must be run for a long time period. This problem led the blade testing laboratories to accelerate fatigue testing time. To achieve the objective, this thesis proposes two novel methods called STFT- and WT-based fatigue damage part extracting methods which are based on short-time Fourier transform (STFT) and wavelet transform (WT), respectively. For WT, different wavelet functions which are Morl, Meyr, Dmey, Mexh and DB30 are studied.
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\nAn aerodynamic computer code, HAWTsimulator, based on blade element momentum theory has been developed. This code is used to generate the sets of aerodynamic loads acting along the span of a ‘SERI-8 wind turbine blade’ in the range of wind speed from cut-in to cut-out. SERI-8 blades are installed on 65 kW wind turbines. Each set of aerodynamic loads is applied on the finite element model of the SERI-8 blade in structural software (ANSYS) to generate a plot of von Mises stress at the critical point on the blade versus wind speed. By relating this relationship to the wind speed data, the stress-time history at the critical point on the SERI-8 blade can be generated. It has the same sampling rate and length as the wind speed data.
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\nA concept of applying accumulative power spectral density (AccPSD) distribution with time to identify fatigue damage events contained in the stress-time history has been introduced in this thesis. For STFT, AccPSD is the sum of power spectral density (PSD) of each frequency band at each time interval in the spectrogram. For WT, AccPSD is the sum of PSD of wavelet coefficients of each scale at each time interval in the scalogram. It has been found that the locations of AccPSD spikes imply where the fatigue damage events are. Based on an appropriate AccPSD level called a cutoff level, the fatigue damage events can be identified at time location of the stress-time history.
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\nA fatigue computer code, HAWTfatigue, based on stress-life approach and Miner’s linear cumulative damage rule has been developed. Basically, the code is used for evaluating the fatigue damage and service lifetime of horizontal axis wind turbine blade. In addition, the author has implemented STFT- and WT-based fatigue damage part extracting methods into the code. Fatigue damage parts are extracted from the stress time history and they are concatenated to form the edited stress-time history. The effectiveness of STFT- and WTbased algorithms is performed by comparing the reduction in length and the difference in fatigue damage per repetition of the edited stress-time histories generated by STFT and WT to those of the edited stress-time history generated by an existing method, Time Correlated Fatigue Damage (TCFD) used by commercial software.
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\nThe findings of this research project are as follows:
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\n1. The comparison of the reduction in length of the edited stress-time histories generated by TCFD, STFT and WT indicates that WT with the Mexh wavelet has the maximum reduction of 20.77% in length with respect to the original length, followed by Meyr (20.24%), Dmey (19.70%), Morl (19.66%), DB30 (19.19%), STFT (15.38%), and TCFD (10.18%), respectively.
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\n2. The comparison of the retained fatigue damage per repetition in the edited stress-time histories generated by TCFD, STFT and WT indicates that TCFD has the retained fatigue damage per repetition less than the original fatigue damage per repetition by 0.076%, followed by Mexh (0.068%), DB30 (0.063%), STFT (0.045%), Meyr (0.032%), Dmey (0.014%), and Morl (0.013%), respectively.
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\n3. Both comparison of reduction in length and comparison in the retained fatigue damage per repetition of the edited stress-time histories suggest that WT is the best method for extracting fatigue damage parts from the given stress-time history. It has also been indicated that not only do STFT and WT improve accuracy of fatigue damage per repetition retained in the edited stress-time histories, but also they provide the length of the edited stress-time histories shorter than TCFD does. Thus, STFT and WT are useful methods for performing accelerated fatigue tests.
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\n4. It has been found that STFT is controlled by two main factors which are window size and cutoff level. Also, WT is controlled by three main factors which are wavelet decomposition level, cutoff level and wavelet type.
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\nTo conclude, the edited stress-time history can be used by blade testing laboratories to accelerate fatigue testing time. STFT- and WT-based fatigue damage part extracting methods proposed in this thesis are suggested as alternative methods in accelerating fatigue testing time, especially for the field of wind turbine engineering.

Most of the available research on horizontal-axis wind turbines focuses on either lab-scale (15–60 cm rotor diameter) or commercial large-scale (80–130 m rotor diameter). The current work fills this gap because residential-scale turbines will be one of the key technologies during the next ten years. The current administration promotes dependence on renewables to cut carbon footprint. Therefore, the present work runs wind tunnel experimentation and performs 48 numerical simulations to evaluate the performance of a residential-scale wind turbine with a blade generated from GOE 447 airfoil at three wind speeds (7.5, 12.5, and 17.5 m/s). Three different vortex generator designs were tested when added on the suction side of a 7-m blade. Two of those designs produced more power than a baseline rotor does (7.2% and 10.9% more power than the baseline rotor were achieved at 12.5 m/s wind speed). Furthermore, three winglet designs were added to the baseline design to investigate their influence on power production. The 90 deg, 60 deg, and 30 deg cant angles produce 5.0%,7.9%, and 6.9% more power than the baseline design.

Reduced frequency effects on combined oscillations, angle of attack and free stream oscillations, for a wind turbine blade element

The formation and evolution of laminar separation bubbles on a horizontal axis wind turbine blade in the transitional flow regime are investigated using Large Eddy Simulations. Both rotating and translating cases of a blade element, based on a small horizontal axis wind turbine, are analyzed to distinguish the specific aerodynamic effects introduced by rotation. The results demonstrated that in the rotating case, the roll-up vortices developed through Kelvin–Helmholtz instability appear shorter, inclined at varying angles along the span, and break down at various locations along the span, in contrast to the continuous two-dimensional structures of the Kelvin–Helmholtz vortices observed in the translating case. Furthermore, in the rotating case, the Coriolis force induces a stabilization of the boundary layer by enhancing momentum transfer, promoting an earlier transition to turbulence and facilitating a rapid reattachment of the flow. Centrifugal force drives radially outward flow, displacing the bubble laterally, restricting its growth and limiting its extent along the blade surface. These effects result in a 66.4% thinner bubble, leading to a 26.7% reduction in lift, and a 36.3% reduction in drag compared to the translating case. These results demonstrate that, unlike large wind turbines, rotation in small horizontal axis wind turbines can degrade lift performance due to reduced effective curvature, despite improving aerodynamic efficiency due to the accompanied drag reduction. This study provides insights into laminar separation bubble behavior under rotation and contributes to a better understanding of the physics, aiding investigations and improvements in performance prediction models for the transitional flow regime.

Numerical investigation of the aerodynamics and wake structures of horizontal axis wind turbines by using nonlinear vortex lattice method

The demand for renewable energy sources is rapidly increasing, with wind energy playing a vital role in sustainable power generation. Horizontal Axis Wind Turbines (HAWTs) are the most widely used configuration; however, they face limitations such as high cut-in wind speed, reduced efficiency at low wind conditions, and mechanical losses during start-up. This project explores methods to enhance the performance of horizontal-axis wind turbines (HAWTs) by integrating permanent‐magnet components. In particular, it investigates how permanent magnets can increase starting torque to lower the turbine’s cut-in wind speed, and how a permanent-magnet synchronous generator (PMSG) can boost electrical conversion efficiency. Combined aerodynamic and magnetic design changes are expected to lower the minimum operational wind speed and raise overall system efficiency. This project proposes the integration of a permanent magnet arrangement into the turbine system to enhance efficiency and overall energy output. The permanent magnets are expected to provide magnetic lift and torque assistance, enabling smoother start-up at lower wind speeds while simultaneously improving generator performance through reduced electrical and mechanical losses.The research involves design and simulation of a modified HAWT system using CAD and analytical tools, followed by prototype development and experimental testing. Comparative analysis will be conducted between the conventional turbine and the magnet-assisted system to evaluate improvements in start-up speed, efficiency, and power generation. The expected outcome is a significant reduction in cut-in wind speed and an overall increase in energy conversion efficiency, making the system more viable in low-wind regions.

This report presents the study of fluid-structure interaction (FSI) of a 5kW horizontal axis wind turbines (HAWT). The motivation of the current investigation is to address the FSI problem of HAWT in the whole flow field analysis with hybrid turbulence model method which is used to find out the flow and structure characteristics of wind turbine in operation under different tip speed ratio (TSR). The target of current work is to obtain detailed information of flow field and structure response simultaneously using the finite element analysis (FEA) method as well as providing new reliable and accurate approach which could be quickly and economically employed in wind turbine FSI problem analysis. In this report, a detailed and comprehensive literature review related to FSI problem of wind turbine has been presented and includes aerodynamic, wind turbine theory, computational fluid dynamic, fluid structure interaction and aeroelastic stability. A 5kW wind turbine is designed according to blade element momentum (BEM) method and a 3D wind turbine modeling is generated in SolidWorks. The 3D wind turbine modeling is imported into FEA software by coupling with the structure domain and the fluid domain to achieve FSI analysis and different TSR are applied to the computational fluid dynamics (CFD) analysis to gain the wind turbine operation information under different scenarios. The simulation results are investigated to reveal the influence of the FSI phenomenon on wind turbine performance. Analysis of wind turbine aeroelastic stability is conducted to prevent blade from experiencing flutter problem. A multiple objective optimization method for wind turbine design including aerodynamic and structure has been developed to improve wind turbine performance. The flow field analysis results showed that the strength of vortex at the tip and root of the blade increases as wind speed increases when wind turbine is under operating conditions. With wind speed of 10m⁄s, most of the flow over the lower surface remains attached and the wind turbine blade was running under design condition. As the wind speed increases, flow separation emerges. When the wind speed increasing to 16m⁄s, the wind turbine blade works under deep stall condition. The wind turbine power coefficient drops continuously from 0.46 to 0.22, as wind speed increased from 10m⁄s to 20m⁄s. The comparison of wind turbine power and torque coefficient under different CFD configuration shows the advantage of whole flow field analysis with hybrid turbulence model. The structural analysis results demonstrated that most of the pressure force acts at a region around the 1⁄4 chord from the leading edge of the blade under operating condition and the displacement of blade tip in flap direction is bigger than those in the other directions. Modal analysis results deduced that flap is the main type of vibration in first and second modes. The difference of natural frequency between single blade and blade rotor becomes larger as vibration order increases. The dynamic performances of wind turbine blade and rotor are totally different and show the whole flow field method is better than the one third domain method. The wind turbine aeroelastic analysis results illustrate that the bending frequency and torsion frequency are around 23.94Hz and 38.46Hz respectively under TSR=4 and both move towards 30Hz under TSR=1.7. When TSR is smaller than 1.7 the wind turbine will experience flutter due to the overlapping of bending and torsion frequencies. The multiple objectives optimization method takes the aerodynamic performance and blade loading into account to gain better design parameter. The comparison between initial and optimal design shows that optimized method could provide higher electrical energy around 1073kW•h per annum under rated wind speed. The optimized wind turbine critical flutter wind speed will increase from initial design speed of 35m/s to 38m/s under optimization design.

This chapter presents the study of wind energy performance using different wind turbine blades. The text contains three different sections of the study. The first of which involves the design of three airfoil-based turbine blades designed and tested in the wind tunnel laboratory. The airfoils were verified independently to investigate the lift and drag forces developed by varying wind velocities through a wind tunnel. The second section of the study is the redesign and improvement of a support structure used to mount each blade being tested in the wind tunnel. An ideal structure will produce no forces or moments that may affect results obtained from the turbine blade. The final portion of the chapter is an improvement of the wind turbine column developed for the extensive testing. This testing was done by putting a strain gauge on the column to test compression and tension during oscillation. If testing shows that the support bar decreases vibration enough, the design was accepted and implemented. Additional improvement to the wind turbine column was the addition of Plexiglas/polycarbonate to supporting the new motor, along with an improved turbine blade hub. This improvement holds the wind turbine in place and increases efficiency that would typically have been lost due to excess movement. The designed hub allows the wind turbine mast to attach to the motor securely. The important discoveries through the improvement of wind turbine blades are discussed toward the end of this chapter.

<abstract> <p>The paper deals with small wind turbines for grid-independent or small smart grid wind turbine systems. Not all small turbine manufacturers worldwide have access to the engineering capacity for designing an efficient turbine. The objective of this work is to provide an easy-to-handle integrated design and performance prediction method for wind turbines and to show exemplary applications.</p> <p>The underlying model for the design and performance prediction method is based on an advanced version of the well-established blade-element-momentum theory, encoded in MATLAB™. Results are (i) the full geometry of the aerodynamically profiled and twisted blades which are designed to yield maximum power output at a given wind speed and (ii) the non-dimensional performance characteristics of the turbine in terms of power, torque and thrust coefficient as a function of tip speed ratio. The non-dimensional performance characteristics are the basis for the dimensional characteristics and the synthesis of the rotor to the electric generator with its load.</p> <p>Two parametric studies illustrate typical outcomes of the design and performance prediction method: A variation of the design tip speed ratio and a variation of the number of blades. The predicted impact of those parameters on the non-dimensional performance characteristics agrees well with common knowledge and experience.</p> <p>Eventually, an interplay of various designed turbine rotors and the given drive train/battery charger is simulated. Criterions for selection of the rotor are the annual energy output, the rotor speed at design wind speed as well as high winds, and the axial thrust exerted on the rotor by the wind. The complete rotor/drive train//battery charger assembly is tested successfully in the University of Siegen wind tunnel.</p> </abstract>

Review of aerodynamic developments on small horizontal axis wind turbine blade

Numerical investigation of sand erosion rate in a horizontal axis wind turbine

As a key component for converting wind energy into electricity, wind turbine blades for early and full process icing detection and prediction can help improve the safety, energy efficiency and economy of the whole wind turbine. In this paper, we propose an Xgboost method for wind turbine blade icing prediction with improved sample distribution to address the problems of large volume, high dimensionality and extremely imbalanced distribution of SCADA data during wind turbine operation. First, similarity analysis and undersampling are performed for most classes of samples, and Adaptive Synthetic Sampling is performed for a few classes of samples to balance the distribution of the dataset. Then the random forest algorithm is used to filter the features of the data set and reconstruct the data features required by the Xgboost algorithm to achieve more accurate wind turbine blade icing prediction. Finally, the model is validated on a real wind power SCADA dataset, and the validation results show that the proposed method for predicting wind turbine blade icing can effectively improve the prediction accuracy in a dataset with extremely imbalanced distribution.