Multi-Megawatt wind turbines have long, slender, and heavy blades that can undergo extreme wind loadings. The aero-elastic stability of wind turbine blades is of great importance in both the power production and the load carrying capacity of structure. This paper investigates the aero-elastic stability of wind turbine blades modeled as thin-walled composite box beam utilizing unsteady incompressible aerodynamics. The structural model incorporates a number of non-classical effects such as the transverse shear, warping inhibition, nonuniform torsional model, and rotary inertia. The unsteady incompressible aerodynamics based on the Wagner’ s function is used in order to determine the aerodynamic loads. The governing differential equations of motion are obtained using the Hamilton’ s principle, and solved using the extended Galerkin’ s method. The results obtained are related to clarification of the effects of angular velocity and wind speed on the aeroelastic instability boundaries of the thin-walled composite beams. The results are expected to be useful toward obtaining better predictions of the aero-elastic behavior of composite rotating blades.

In the present study, block-diagram simulation of a reference horizontal axis wind turbine with pitch-regulated mechanism is presented. The aim of this simulation is modeling of wind turbine subsystems to investigate the transient behavior of the turbine under unsteady incoming wind. Analytical approximation model is used to estimate the output power coefficient. In addition, PID controller is imposed to regulate the output power via changing the blade pitch angle. Governing equations of the mechanical part (i. e. gearbox), electrical part (i. e. three-phase doubly fed induction generator), aerodynamic and controller models are implemented in LMS AMESim software package. The model uses a purely torsional multi-body simulation to show the dynamic behavior of gearbox. The proposed model is used to investigate the rotor transient behavior as well as the controller performance under the conditions that the wind speed changes linearly from 21 to 8 m/s during 130 seconds. The results show acceptable accuracy in comparison with the reference data.

The blade element momentum (BEM) theory has been employed to examine the aerodynamic parameters such as lift, drag, and thrust coefficient. Tip loss factor is one of the most important parameters to improve BEM theory. Glauert and Prantl represented different expression for tip loss factor which have been used commonly at literature. But the measurements and theoretical analyses show that existing tip loss factor are inconsistent and fail to predict correctly the physical behavior in the blade tip. A new tip loss factor has proposed by Shen that remedies the inconsistency. In this study, Shen formula as the newest tip loss factor has been utilized to analyze thirteen different airfoils performance. The results indicate that the blade with the RISØ-A1-24 airfoil has the shortest chord length, approximately 1.8 meters, which is considered a significant advantage due to reduced material weight and construction costs. Moreover, the RISØ-A1-24 and FFA-W3-211 Free Transition airfoils are the most effective in terms of power generation, as their total power coefficient values versus tip speed ratio changes are higher compared to other airfoils. Additionally, airfoils such as FFA-W3-241 and S814, which reach their maximum power coefficient at lower tip speed ratios, are suitable for areas with lower average wind speeds.

Regarding the suitable potential for wind energy in Iran, it is possible to employ small wind turbines such as large ones to supply part of the electricity load of the country. The present study deals with materials used in small horizontal axis wind turbine blades and their fabrication methods. To this end, the wood and the composite, as the two main materials used in blades, have been investigated. Then, the main methods of producing wooden and composite blades have been analyzed. Finally, the 3D printing method and polymer materials used in this technique have been introduced. The study shows that the fatigue parameter has an important role in determining the blade’s material and the fabrication method. Despite the environmental benefits of using wood, the complexity and the manufacturing costs prevent rapid and affordable production of wooden blades. On the other hand, the mass production of composite blades is more economical, although it has environmental impacts. Despite the fatigue issue of the 3D printed blades, the 3D printing method is a fast and relatively inexpensive technique for fabrication of small wind turbine models for wind tunnel tests.

In this paper, equations of motion for a horizontal axis wind turbine with movable base are extracted and natural frequencies and vibration of the system are studied. The wind turbine tower is assumed rigid while its blades are modeled as flexible beams. In-plane bending and twisting are considered as two degrees of freedom for blades motion. The shaft connected the tower to blades is assumed rigid and its rotational velocity is considered. In this paper, specifically, a 5-megawattfloating horizontal axis wind turbine, which it’s base has three angular velocities in different directions, is studied. Due to the complex shape and variation of the properties along the length, the turbine blade properties such as mass per lenght and geometric parameters are extracted by curve fitting in MATLAB. The equations of motion and boundary conditions are derived by Hamilton's principle and then are transformed to ordinary differential equations by Galerkin method. By setting the governing equations to standard form (space state), eigenvalues and frequencies are calculated. The numerical results are compared with published results and good agreement is observed. Then the effect of various parameters on turbine blades frequencies and time responses are demonstrated. Results show that the tower base angular velocity and blades rotational speed have considerable effects on turbine blades time response and vibration frequencies.

Today, research on road accidents, especially in horizontal arches, is considered a scientific and applied research. Researchers have come to the conclusion that accidents are not just a specific cause but a series of different causes and events, both human and nonhuman. The purpose of this study is to identify and localize the causes of accidents in horizontal arches on the Babamidan-Basht axis. The research method is descriptive-survey in terms of implementation and applied research in terms of purpose, which has been done quantitatively. Because the subject of the present study is a specific topic in the field of roads (engineering and road construction), non-probabilistic sampling is of a judgmental type. The statistical population of the study includes 12 experts, experts and engineers in the field of road construction in Fars province. In this research, by studying the latest previous domestic and foreign research as well as field research, the causes of accidents in horizontal arches have been identified and then localized using the opinion of experts and fuzzy Delphi method. After distributing and analyzing the questionnaires, the result was that out of 22 identified factors for the occurrence of accidents in horizontal arches, according to experts, 13 factors for the Babamidan-Basht axis were finally confirmed. At the end of the research, in line with localized factors, some practical suggestions for improving and reducing accidents in the horizontal axes of Babamidan-Basht axis are presented.

The wake and the lack of existing velocity behind the wind turbine affect the energy production and the mechanical integrity of wind turbines downstream in the wind farms. This paper presents an investigation of the unsteady flow around a wind turbine under yawed condition. The simulations and experimental measures are made for the yaw angle rotor 30° and 0°. The wind velocity is 9.3 m/s and the rotation velocity rotor of the wind turbine in 1300, 1500 and 1800 rpm. The wind turbine rotor which is modeled is of a commercial wind turbine i.e. Rutland 503. The approach Improved Delayed Detached Eddy Simulation (IDDES) based on the SST turbulence model is used in the modeling of the flow. The solutions are obtained by using the solver which uses finite volume method. The particle image velocimetry (PIV) method is used in wind tunnel measurements in the experimental laboratory of the ENSAM Paris-Tech. The yawed downstream wake of the rotor is compared with that obtained by the experimental measurements. The results illustrate perfectly the development of the near and far wake of the rotor operation. It is observed that the upstream wind turbine yawed will have a positive impact on the power of the downstream turbine due the distance reduction of the downstream wake of the wind turbine. However the power losses are important for yawed wind turbine when compared with the wind turbine without yaw. The improved understanding of the unsteady environmental of the Horizontal Axis wind Turbine allows optimizing wind turbine structures and the number of wind turbines in wind farms.

In this paper, the air flow around a root airfoil model of horizontal axis wind turbine, namely SG6040 is numerically simulated using finite volume method by three turbulence modelling k-ω, k-ω SST, and Spalart-Allmaras in two Reynolds Number of 137,122 and 149,969 and at 0 to 10 degrees angles of attack. The main objective of this paper is to provide a proper numerical model for simulating the root airfoils of wind turbines with small rotor sizes. Also, the effect of angles of attack and Reynolds number on aerodynamic coefficients were investigated and the results were compared with each other. The results show that the k-ω SST turbulence model presents better results than other models and is more consistent with experimental results. Also, by increasing Reynolds number, turbulence models seem to have the same trend and the greatest differences occur in the low Reynolds numbers. The results obtained in this case study can play a significant role in designing wind turbine blades.

In this paper, boundary layer control technique is investigated on the NREL-5MW offshore baseline wind turbine blade with numerical simulation of linear DBD plasma actuator in a three-dimensional manner. This wind turbine uses pitch control system to adjust its generated power above its rated speed; but below that the controller is inactive. In the current study, operating condition is set such that the control system is off. Plasma actuator consists of two electrode and dielectric materials. One of these electrodes is connected with the air and another one is encapsulated with the dielectric material. When the necessary high-level AC voltage is applied to electrodes, electric field forms around the actuator and an induced wall jet forms with the ionization of the air around the actuator. Electrostatic model is applied to simulate the effects of plasma actuator and the resulted body force is inserted into flow momentum equations. In the present study, three different control cases are studied. Results show that in all cases, using this actuator leads to improvement of the velocity profile in controlled section, which influences on pressure distribution and results in rotor torque increment. Finally, increasing in torque leads to growth in produced power of the wind turbine. The highest increment in output power occurs when the actuator is installed near the root of the blade in the spanwise direction and before low-speed region in the chordwise direction.

Since the renewable resources of energy have become extremely important, especially wind energy, scientists have begun to modify the design of the wind turbine components, mainly rotor blades. Aerodynamic design considered a major research field related to power production of a small horizontal wind turbine, especially in low wind speed locations. This study displays an approach to the selection of airfoil and blade design utilized in small horizontal wind turbines with low cut-in speed and with no gear box. Modeling of the flow depends on Computational Fluid Dynamics (CFD) and theory of Blade Element Momentum (BEM) methodologies. QBlade used (BEM) for wind turbine simulation and integrated with XFOIL for airfoils design to ensure the requested characteristics for wind turbine performance. MATLAB is used to calculate the final design parameters to be modeled in SOLIDWORK. The flow dynamics are explored with the aid of ANSYS Fluent 16. The application of specially designed blades grants start up at lower wind speeds. The designed blade is fabricated from polyurethane foam. Experimental study confirmed that, at low average wind velocity (4 m/s), the fabricated small-scale horizontal wind turbines are considered to be a positive way to supply electricity with an average power rate of 9 watt and efficiency of 8 %.