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Guest Editorial

J. Energy Resour. Technol. 2015;137(5):050301-050301-1. doi:10.1115/1.4031324.

This special issue contains selected papers presented at the First International Conference on Next Generation of Wind Energy (ICNGWE-2014). The conference was held at Universidad Europea de Madrid (UEM), Spain, during Oct. 7–10, 2014. The sponsors included National Science Foundation, Virginia; CD-adapco, New York; Gas Natural Fenosa, Madrid, Spain; Aldesa Energias Renovables, Madrid, Spain; Edibon, Madrid, Spain; Universidad Europea de Madrid, Spain; Lund University, Sweden; and University of Wisconsin–Milwaukee, Wisconsin.

Topics: Wind energy
Commentary by Dr. Valentin Fuster

Research Papers: Alternative Energy Sources

J. Energy Resour. Technol. 2015;137(5):051201-051201-10. doi:10.1115/1.4030109.

The vast dimensions of the renewable energy field have drawn diverse approaches, resources, and results for a long time. The continual changing behaviors and cycles of renewable energy have encouraged novel developments over the years with most commonly used approaches being three blade designs mounted on a rotor and are commonly used to harvest onshore and offshore wind energy. The renewable energy field is extremely dynamic and perplexing, thus creating a heavy interest in discovering the most economical, efficient, and reliable method to harvest renewable wind energy. Producing energy through the wind is well proven and widely used method with current activities focused on improving efficiency, performance, and reliability. A major challenge of wind energy is that it is available only when and where winds prevail. The electricity produced must be used instantly or stored for use in times when none to limited winds exist. The developments of blades have been based on the aircraft propeller design but extended over a larger area to capture much energy from the wind. This paper provides some basic guidelines on the optimum design staring from the historical design, recent developments, and opportunities. Some challenges on trends are discussed with novel ideas of some future wind energy harvesting designs for enhanced applications at greater efficiency.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2015;137(5):051202-051202-5. doi:10.1115/1.4029912.

Wind turbine blades undergo fatigue and their performance depletes as time progresses due to the formation of internal cracks. Self-healing in polymers is a unique characteristic used to heal the cracks inherently as they form. In this study, a new method is demonstrated for supplying the monomer (that is quintessential for the healing process) uniformly throughout a fiber reinforced polymer composite. Commercial tubes were used to produce a vascular network for increased accessibility of the healing agent. The tube layouts were varied and their effect on the composite structure was observed. Conventional glass fiber reinforced polymer matrix composites (PMC) without microtubing were tested using dynamic mechanical analysis (DMA) to study the flexural visco–elastic behavior. The vascular network arrangement coupled with DMA data can be used to uniformly supply appropriate amount of healing agent to implement Self-healing in fiber reinforced PMC.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2015;137(5):051203-051203-10. doi:10.1115/1.4030352.

A review on icing physics, ice detection, anti-icing and de-icing techniques for wind turbines in cold climate has been performed. Typical physical properties of atmospheric icing and the corresponding meteorological parameters are presented. For computational modeling of ice accretion on turbine blades, the LEWINT code was adopted to simulate ice accretion on an aerofoil for a 2 MW wind turbine. Ice sensors and the basic requirements for ice detection on large blades are described. Besides, this paper presents the main passive and active ice mitigation techniques and their advantages and disadvantages. Scope of future work is suggested as wind turbine blades scale up.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2015;137(5):051204-051204-5. doi:10.1115/1.4030444.

Scour compromises the operation of offshore facilities. This article describes the results of an investigation aimed at the analysis of different methods used in the scour protection systems design at offshore wind farms. The study is focused on transitional waters, where monopile foundations present medium or large diameters. Using the experience of offshore wind farms currently installed, a new design formula is proposed. All of this with the aim of improving a preliminary design of scour protection systems considering maritime parameters.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2015;137(5):051205-051205-6. doi:10.1115/1.4030399.

Despite being harvested thousands of years ago, wind energy was neglected during the industrial revolution because of the strong dependence on fossil fuels. However, after the alarming decrease in the fossil fuels reserves, many have drawn their attentions back to a renewable energy technology, especially the wind energy. This paper presents some of the new designs that are being tested, including slotted blades and tubercles design models. The experimental results are used to validate the numerical studies that are being conducted parallel to the experiments for better understanding and more detailed results. The new slotted blade design produced more power compared to the straight blade for lower wind speeds, while the tubercle blades showed better power performance in severe wind conditions and a more steady behavior under unsteady and higher wind velocities.

Topics: Blades
Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2015;137(5):051206-051206-8. doi:10.1115/1.4030445.

This paper presents a method for optimizing blade designs in smart rotors; the objective is to maximize power regardless of wind conditions. An extensive analysis of what is known as “smart blades,” from aeronautical solutions and helicopter rotors is provided. Moreover, trends in computational and experimental research are analyzed, an assessment and categorization of the options available for aerodynamic control surfaces are made. The study and analysis of its main components such as sensors, mechanisms of actuation, and materials are included. Advance research in this technology is presented as a potential solution for more efficient blade designs, and methods for reducing aerodynamic loads are discussed.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2015;137(5):051207-051207-12. doi:10.1115/1.4030448.

This paper presents the results of a wide experimental study on an H-type vertical axis wind turbine (VAWT) carried out at the Politecnico di Milano. The experiments were carried out in a large-scale wind tunnel, where wind turbines for microgeneration can be tested in real-scale conditions. Integral torque and thrust measurements were performed, as well as detailed aerodynamic measurements to characterize the flow field generated by the turbine downstream of the rotor. The machine was tested in both a confined (closed chamber) and unconfined (open chamber) environment, to highlight the effect of wind tunnel blockage on the aerodynamics and performance of the VAWT under investigation. The experimental results, compared with the blockage correlations presently available, suggest that specific correction models should be developed for VAWTs. The experimental thrust and power curves of the turbine, derived from integral measurements, exhibit the expected trends with a peak power coefficient of about 0.28 at tip-speed ratio equal to 2.5. Flow measurements, performed in three conditions for tip speed ratio equal to 1.5, 2.5, and 3.5, show the fully three-dimensional character of the wake, especially in the tip region where a nonsymmetrical wake and tip vortex are found. The unsteady evolution of the velocity and turbulence fields further highlights the effect of aerodynamic loading on the wake unsteadiness, showing the time-dependent nature of the tip vortex and the onset of dynamic stall for tip speed ratio lower than 2.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2015;137(5):051208-051208-11. doi:10.1115/1.4030617.

Much of the aerodynamic design of wind turbines is accomplished using computational tools such as XFOIL. These codes are not robust enough for predicting performance under the low Reynolds numbers found with small-scale wind turbines. Wind tunnels can experimentally test wind turbine airfoils to determine lift and drag data over typical operating Reynolds numbers. They can also test complete small wind turbine systems to determine overall performance. For small-scale wind turbines, quality experimental airfoil data at the appropriate Reynolds numbers are necessary for accurate design and prediction of power production.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2015;137(5):051209-051209-10. doi:10.1115/1.4031005.

The impacts of swells on the atmospheric boundary layer (ABL) flows and by this on the standalone offshore wind turbine (WT) performance are investigated by using large eddy simulations (LES) and actuator-line techniques. At high swell to wind speed ratio, the swell-induced stress reduces the total wind stress resulting in higher wind velocity, less wind shear, and lower turbulence intensity level. These effects increase by increasing swell to wind speed ratio (C/U) and/or swell steepness. Moreover, for the same hub-height wind speed (Uhub), the presence of swells increases the turbine power extraction rate by about 3% and 8.4% for C/Uhub = 1.53 and 2.17, respectively.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2015;137(5):051210-051210-12. doi:10.1115/1.4031043.

Use of wind turbines is rapidly growing because of environmental impacts and daily increase in energy cost. Therefore, improving the wind turbines' characteristics is an important issue in this regard. This study has two objectives: one is investigating the aerodynamic performance of wind turbine blades and the other is developing an efficient approach for shape optimization of blades. The numerical solver of flow field was validated by phase VI rotor as a case study. First, flow field around the wind turbine blades was simulated using computational flow dynamics (CFD) and blade element momentum (BEM) methods, then obtained results were validated by available experimental data to show an appropriate conformity. Then for yielding the optimal answer, a shape optimization algorithm was used based on artificial bee colony (ABC) coupled by artificial neural networks (ANNs) as an approximate model. Effect of most important parameters in wind turbine, such as twist angle, chord line, and pitch angle, was changed till achieving the best performance. The flow characteristics of optimized and initial geometries were compared. The results of global optimization showed a value of 8.58% increase for output power. By using pitch power regulate, the maximum power was shifted to higher wind speed and results in a steady power for all work points.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2015;137(5):051211-051211-6. doi:10.1115/1.4030316.

Despite the growth of the offshore wind industry, there are currently doubts relating to the design of wind facilities in the sea. This paper expounds current, already identified structural uncertainties: problems for soil characterization and transition piece (TP) design. This document also introduces new doubts or issues to be researched in the near future in this field (wave theory, scour process, wave load actions, scale difficulty, etc.), not as yet identified due to the scarce experience in the offshore wind industry. With this in mind, technical offshore wind standards related to foundation design have been reviewed.

Commentary by Dr. Valentin Fuster

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