Bladelets-Winglets on Blades of Wind Turbines: A Multiobjective Design Optimization Study

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.

The influence of the time-varying internal tensile force is utilized to suppress the edgewise vibration of the wind turbine blade. The National Renewable Energy Laboratory (NREL) 5-MW baseline wind turbine is considered for numerical simulation. Based on the energy approach, an Euler-Lagrangian wind turbine mathematical model is developed including time-varying internal tensile force in the blade, and the interaction between the edgewise and flap-wise behavior of the blade and tower. Using Lagrange’s approach, the equations of motion for the edgewise and flap-wise directions are derived for both the blade and tower. The wind turbine model is subjected to aerodynamic loading which is simulated using the classical Blade Element Momentum (BEM) theory based on the aerodynamic properties of the blade under quasi-static conditions. The Kaimal turbulence model is also incorporated to get the edgewise fluctuating components of the wind, experienced by the rotating wind turbine blade. The increasing tensile force diminishes the peak, root mean square (RMS), and peak-to-peak values of the edgewise displacement of the blade at the tip. The results demonstrate the notable ability of the time-varying internal tensile force to mitigate the edgewise vibrations, suggesting that the proposed system holds promise for the wind turbine blades.

This paper presents an optimization model for rotor blades of horizontal axis wind turbines. The model refers to the wind speed distribution function on the specific wind site, with an objective to satisfy the maximum annual energy output. To speed up the search process and guarantee a global optimal result, the extended compact genetic algorithm (ECGA) is used to carry out the search process. Compared with the simple genetic algorithm, ECGA runs much faster and can get more accurate results with a much smaller population size and fewer function evaluations. Using the developed optimization program, blades of a 1.3 MW stall-regulated wind turbine are designed. Compared with the existing blades, the designed blades have obviously better aerodynamic performance.

A biomimetic wind turbine inspired by Dryobalanops aromatica seed: Numerical prediction of rigid rotor blade performance with OpenFOAM®

As wind energy continues to expand to new frontiers in terms of the location, number, and size of wind turbines, the industry has begun to seek smarter operations and management solutions. Wireless sensing nodes could provide a low-cost platform to support a variety of applications designed to reduce the levelized cost of energy and increase the safety of wind turbines. However, a wireless sensor node deployed on a wind turbine blade would have an extremely limited energy supply. To combat this limitation, we present BladeMAC, a new MAC-layer protocol designed for sensor nodes deployed on rotating wind turbine blades. BladeMAC overcomes a unique cyclical channel problem to allow a sensor node attached to a rotating blade to opportunistically and efficiently offload its data to a sink node attached to the turbine tower. We have implemented and evaluated BladeMAC using Contiki OS and the Cooja simulation tool. We present results showing that BladeMAC effectively deals with the cyclical channel problem at a wide range of data arrival intervals, and that BladeMAC is insensitive to rotation speed and rotation speed fluctuations.

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.

This paper has attempted to study a mechanism of three-dimensional flow around a horizontal axis wind turbine (HAWT) rotor blade. An experimental study of the flow phenomenon in the vicinity of the wind turbine blade is a challenging endeavor. In this research, the HAWT model with 2.4 m diameter was tested in the large wind tunnel. The flow around the rotating blade surface was measured simultaneously for three velocity components, and two probes were used for the synchronized measurement of three-dimensional flow components. The local velocity was detected for the single seeding particle measured in the point where three pairs of laser beams intersected. Blade sections of interest in this study are composed of radial positions r/R = 0.3, 0.5 and 0.7. Optimum and low tip speed ratio flow characteristics were also compared. The velocity flow vector, skin friction coefficient and bound circulation were calculated from LDV measurements, and the experimental research showed reasonably and clearly the experimental results.

Increasing levels of modernization in different countries worldwide have lead to an exponential growth in national energy demand. India with its huge population base had a total grid connected electric power close to 285 GW during 2015 with annual generation of 1106 TWh accounting to a per-capita energy consumption of 746 kWh. The Government of India under its ambitious plan “Power for all” envisages 24 × 7 power supply for the entire domestic and Industrial loads by the year 2022. This power sector initiative also promises the generation through green path by targeting reduction in carbon footprint. The plan has sanctioned funds for production of 190 GW power based on go green initiative of United Nations Organization and a step forward to create a better environment for future generations. The proposed work aims at design of wind-solar hybrid system for light load decentralized applications. The computational tools were used to model and analyze wind turbine (WT) blade structure for low power applications to suit decentralized power generation based on renewable energy. The comparative studies of test aerofoil with standard NACA 0018 aerofoil indicated conformance of the test aerofoil as a profile for WT blades. The test aerofoil has the feature of easier manufacturability as against standard NACA 0018 profile adopted in commercial WT blades. The studies conformed suitability of test profile at specified angle of attack with WT blade structure and hub construction using balsa wood. The choice of balsa wood was based on properties of lighter weight and adequate strength that was supported on the designed tower of tripod type. The designed WT system was for a rated power output of 75 W while operating at an average wind speed of 4.5 m/s. The system developed will be a feasible option for powering households in rural India.

A qualitative analytical investigation of geometrically nonlinear effects in wind turbine blade cross sections

The placement of a cylindrical body in a flow alters the velocity and pressure fields resulting in a local increase in the flow speed near the body. This interaction is of interest as wind turbine rotor blades could be placed in the area of increased wind speed to enhance energy harvesting. In this work the aerodynamic performance of two short aspect ratio (AR = 0.93) cylindrical bodies was evaluated for potential use in “accelerated wind” applications. The first cylinder was smooth with a constant diameter. The diameter of the second cylinder varied periodically along the span forming channels, or corrugations, where wind turbine blades could be placed. Experiments were performed for Reynolds numbers ranging from 1 × 105 to 9 × 105. Pressure distributions showed that the smooth cylinder had lower minimum pressure coefficients and delayed separation compared to the corrugated cylinder. Velocity profiles showed that the corrugated cylinder had lower peak speeds, a less uniform profile, and lower kinetic energy flux when compared to the smooth cylinder. It was concluded that the smooth cylinder had significantly better potential performance in accelerated wind applications than the corrugated cylinder.

The need for energy and electricity has been increasing globally, and this means more power is required from the power plants. Power plants, however, will then continue harming the earth because of the greenhouse gasses produced while generating energies that contribute to global warming. Using renewable sources to produce clean energies is one of the sustainable methods to deal with such challenges. Wind energy is one of the renewable sources, which is accessible anywhere on earth, creating green energy. Wind turbines are mainly categorized into Horizontal Axis Wind Turbines (HAWT) and Vertical Axis Wind Turbines (VAWT). This paper firstly presents a general comparison between the HAWTs and VAWTs. Then, it presents mathematical modelling for the aerodynamic factors of HAWT and Darrieus VAWT to assist the researchers to understand some key design aspects of wind turbines, such as lift/drag ratio, tip speed ratio, power coefficient, and torque coefficient. Also, this paper presents a review of the aerodynamic performance of the recent VAWT designs to help researchers to identify and choose the best model among the Savonius and Darrieus rotors for further development or designing a new model at different wind conditions. This comparison review shows that for a large scale HAWT upwind 3 bladed wind turbines are the most optimum. The helical Savonius rotors perform better by having positive torque coefficient at all azimuth angles. Moreover, helical Darrieus was found to produce lesser noise and suitable for conventional areas. hybrid Savonius-Darrieus rotors can solve the self-starting challenge of the VAWTs, and they are suitable at low wind speeds. At last, this review shows some of the recent hybrid Savonius-Darrieus rotors which would help to solve the low efficiency of Savonius rotor and self-starting challenge of Darrieus rotors.

This paper investigates the potential of deploying flaps on wind turbine blades to enhance their efficiency and energy capture capabilities. The FX66-S-196V, FX63-137 S, and SG6043 supercritical airfoils were used and distributed along the blade radius. Flaps, situated 20% along the trailing edge of the blade chord, offer a means of actively controlling aerodynamic forces and optimizing blade performance under varying wind conditions. Through computational fluid dynamics (CFD) simulations and optimization techniques. The aerodynamic effects of flap deployment on wind turbine blades are analyzed. The study explores the impact of flap angle, position, and deployment strategy on key performance metrics such as power coefficient, lift-to-drag ratio, and energy extraction efficiency. Results demonstrate that judiciously deploying flaps can lead to significant improvements in turbine efficiency, with power output enhancements ranging from 2.5% to 4.6%, depending on operating conditions such as wind speed, tip speed ratio, angle of attack, and flap angle setting. Furthermore, sensitivity analysis reveals optimal flap configurations for different wind regimes, highlighting the importance of adaptive control strategies. This research contributes to the growing body of knowledge on active aerodynamic control techniques for wind turbine optimization and underscores the potential of flaps as a viable means of enhancing wind turbine blade efficiency in practical applications.

Icing condition prediction of wind turbine blade by using artificial neural network based on modal frequency

This research investigated and optimized the separation of carbon dioxide (CO2) from natural gas in an adsorption column filled with grafted-beam nanofiber adsorbent. The main purpose of using ANN and RSM models in this manuscript is to compare these two methods in predicting the CO2 adsorption capacity. In other words, it was made to find a suitable model that has the highest agreement with the experimental data. Also, the other purpose of using the RSM model is to detect the optimized empirical conditions. Moreover, two common ANN models are applied in this work, including a multilayer perceptron (MLP) and radial basis function (RBF). The novelties of this work are explained as follows: (1) detecting the optimized synthesis factors of NF-PAN/PUGMA sorbent which possess the highest CO2 adsorption capacity with the help of response surface methodology (RSM), (2) studying the simultaneous interaction of synthesis parameters on the CO2 adsorption capacity with the help of both RSM and artificial neural networks (ANNs), (3) testing two types of ANN models including multilayer perceptron (MLP) and radial basis function (RBF) to predict the effect of monomer volume percentage and irradiation dose on the CO2 adsorption capacity. Indeed, finding the best model (ANN or RSM) can help engineers in practical applications predict CO2 adsorption capacity using NF-PAN/PUGMA under different conditions without incurring high-priced chemical materials, electricity, or human resources. The validation results were examined using correlation coefficients (R2) of RSM, RBF, and MLP models. The correlation coefficients for the RSM, RBF, and MLP models were 0.9910, 0.9949, and 0.9968, respectively. Additionally, the average absolute relative deviation (AARD) values for the RBF and MLP models were 0.00046512 and 0.00045511, respectively, indicating that the MLP model is better than the RBF model. To identify the optimal network structure, the trial-and-error method was conducted for MLP and RBF models. The number of neurons was found at 12 and 45 for MLP and RBF, respectively. The optimized effective parameters were obtained using RSM: 25.80% GMA, 66.45% amine, and an irradiation intensity of 28kGy.

The goal of this research is to redesign the three-dimensional geometry of a micro horizontal-axis wind turbine blade using response surface methodology. The variation of the two influential design parameters, chord length and twist angle, along the blade is geometrically modelled using a fourth- and second- degree polynomial, respectively. Therefore, the optimization process is performed basing on eight input parameters that describe the initial blade design. The performance of the initial and the new optimized wind turbine are compared using CFD and BEM approaches. To well study fluid flow through the wind turbine and assess its performance, the CFD analysis step is carried out using the RANS equations with the k-ω SST turbulence model. Concerning the optimization step, The MOGA (Multi-Objective-Genetic Algorithm) method is employed in an automated manner based on a metamodel with non-parametric regression NPR to identify the best candidate with high efficiency. The performance of turbine rotor types is analyzed using the open source Qblade software and compared with CFD methodology for different TSR (Tip Speed Ratio) values. An increase of 14.65% and 17.17% in power coefficient is marked for CFD and Qblade, respectively, at the design TSR of 3. Compared to the initial blade, the optimal one produces more lift, has a lower separation area, and performs significantly better performance at all TSR values. The detailed representation of 3D flow via pressure distribution and limiting streamlines on both blade surfaces confirm the optimization target which leads to reduce separation zones and improve rotor torque. Additionally, a 37% improvement in starting operability at the lowest wind speed is achieved compared to the initial rotor.