Wind blades

Composite adhesives are being used for a growing number of applications outside the automotive industry as well. For example, Dow Formulated Systems recently developed a foam core system for wind blades that is bonded by epoxy adhesives. The new system offers long-term dynamic behavior and shear strength properties that deliver the excellent mechanical strength and fatigue resistance necessary to achieve blade durability. 

Global Energy Concepts of Dayton, OH, USA is using carbon fiber prepreg for large wind blades for the Vestas 90 m long blade. This... 

Sharp, K., Bogdanovich, A., Boyle, R., Brown, J., Mungalov, D., 2013. Wind blade joints based on non-crimp 3D orthogonal wovrai H shaped preforms. Compos. Part A 49, 9-17. 

Large aircraft program Wind blade Automobile, oil mine... 

J. R. Hazen (2003) Carbon/fiberglass wind blades planned, High-Performance Compos. 11,13. 

Today the coin-tap test is a widely used technique on wind turbine rotor blades for inspection of thin GFRP laminates for disbonded and delaminated areas. However, since the sensitivity of this technique depends not only on the operator but also on the thickness of the inspected component, the coin-tap testing technique is most sensitive to defects positioned near the surface of the laminate. Therefore, there has been an increasing demand for alternative non-destmctive testing techniques which is less operator dependent and also more sensitive to delaminations and disbonded areas situated beyond thicker GFRP-laminates. 

Fig. 1. Simple illustration of the basic design of the wind turbine rotor blade scanner.

Based on a preliminary set of acceptance criteria s developed by LM Glasfiber a standard data-set has been developed for each of the above mentioned set-ups, in order to minimize the scanning time. During the performance demonstration at LM Glasfiber the effective scanning time for a complete 21m wind turbine rotor blade based on the preliminary acceptance criteria s, was found to be less than hour. 

After the performance demonstration a number of damaged rotor blades were scanned followed by a number of destructive verifications of the results achieved by ultrasonic scanning. Based on this examination it was concluded that the wind turbine rotor blade scanner is capable of detecting defects such as delaminations, inclusions, missing adhesion, lack of adhesive, porosities and variations in thickness. 

J. Rusborg, Non-Destructive inspection of wind turbine rotor blades, part I (In Danish) FORCE Institute 1995, ISBN 87-7784-049-6... 

Fig. 1. Categories of wind machines (a) Darrieus machine (b) two-bladed machine (c) three-bladed machine and (d) Savonius machine. Parts (e) and (f)...

On the positive side, the three-dimensional nature of the resource provides it with a distinct advantage compared to other solar technologies. Specifically, because siting usually involves placing the individual turbines as high as possible, typically spacing turbines about 2 to 3 blade diameters apart crosswind and 10 diameters apart downwind, only a small fraction of a wind farm area is actually occupied. The rest of the land remains available for other appHcations, such as crop production or Hvestock grazing. 

The electricity generated depends primarily on the speed of the wind at the site of installation. A conventional formula to determine the wind energy, based on the design of the rotor (rotating blades) and the site conditions is given by... 

Cut-in wind speed is the minimum wind speed at which the generator commences the generation of power. At this speed the brakes release and the prime mover (blades) starts rotating. 

Cut-oul wind speed is the maximum w ind speed beyond which the prime mover may overspeed above its permissible limits. As the structure and the blades are designed for a particular maximum speed, a wind speed higher than this may exceed their mechanical endurance and become unsafe. At this speed the brakes apply and the machine is disconnected from the grid. The cut-in and cut-out speeds define the wind speed limits within which the turbine will work safely through the generator. Rated wind speed is the speed at which the prime mover rotates at the rated negative slip and generates the rated power. 

The NACA 65 blade profiles were tested in a systematie manner by Herrig, Emery, and Erwin. The easeade tests were earried out in a easeade wind tunnel with boundary-layer suetion at the end walls. Tip effeets were studied in a speeially designed water easeade tunnel with relative motion between wall and blades. 

The vane anemometer is an old invention. It can be likened to a small wind turbine with 4-10 rotating blades and a handle, as in Fig. 12.20. Earlier constructions were fully mechanical, where the spindle rotation was transmitted to a pointer through a series of gears. In modern vane anemometers, an electrical sensor records the spindle rotation and the signal is processed, giving the velocity on a digital display. Such an instrument usually is able to integrate the mean velocity over a time interval. 

Diffusion was veiy slow. The earliest clear Chinese reference to a windmill occurs only in 1219. The Chinese adopted the horizontal rotor used in Central Asia, but equipped it with pivoted blades, like Venetian blinds. These windmills did not require shielding walls like Central Asian mills, and could tap wind from any quarter. 

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