Blade Design, Manufacture, and Testing

Abstract

In Chap. 5 it was shown that the design of an optimum power-extracting blade is straightforward, at least when tip losses can be ignored. However, the last chapter highlighted the importance of starting for small wind turbine blades, and the associated issues of resistive and aerodynamic torque. It was shown that the optimum-power blade is always very slow to start, and by implication, will have poor low wind performance. In this chapter the dual requirements of good starting and efficient power extraction are addressed using a numerical optimisation method called “differential evolution”, DE. It is shown that, generally, a small reduction in efficiency can result in a large reduction in starting time, and that this is a good strategy for a blade designer to follow. The manufacture of blades with their complex three-dimensional shape is then discussed. It is shown that timber is an excellent material for blades less than about 1 m in length, but some of the many forms of composites are preferable for larger blades. As the most critical turbine component for safety, blades must be thoroughly tested. The three classes of test—the material, blade static and fatigue tests—are described.