Abstract
This paper describes a computer method to allow the design of small wind turbine blades for the multiple objectives of rapid starting, efficient power extraction, low noise, and minimal mass. For the sake of brevity, only the first two and the last objectives are considered in this paper. The optimization aimed to study a range of blade materials, from traditional fibreglass through sustainable alternatives to rapid prototyping plastic. Because starting performance depends on blade inertia, there is a complex interaction between the material properties and the aerodynamics. Example blades of 1.1 m length were designed to match a permanent magnet generator with a rated power of 750 W at 550 rpm. The materials considered were (a) traditional E-glass and polyester resin; (b) flax and polyester resin; (c) a typical rapid prototyping plastic, ABS-M30; and (d) timber. Except for (d), hollow blades were used to reduce the rotor inertia to help minimize starting time. Two airfoils are considered: the 10% thick SG6043 which has excellent lift:drag performance at low Reynolds number and the SD7062 whose extra thickness (14%) has some structural advantages, particularly for the weaker material (c). All blade materials gave feasible designs with material (d) the only one that required a blade shell thickness greater than the specified minimum value of 1% of the blade chord. Generally, the blade chord and twist increased as starting was given greater importance. In all cases, the associated increase in blade inertia was outweighed by the larger aerodynamic torque. Materials (a), (b), and (d) were better suited to the SG6043 airfoil whereas ABS-M30 benefitted from the thicker SD7062 section.
Highlights
Small wind turbines are under strong competitive pressure from photovoltaics (PV) which have decreased significantly in price over the past decade
The SG6043 airfoil produces more power but the approximately 2% difference is not as large as the difference in the lift to drag ratio shown in Figure 1 and may not be observable in practice
This paper describes a multi-objective optimization program for small wind turbine blade design in which the optimization can be of any combination of maximum power and minimum noise, starting time, and structure
Summary
Small wind turbines are under strong competitive pressure from photovoltaics (PV) which have decreased significantly in price over the past decade. There are two aspects of small wind turbines that will remain attractive. The first is that remote renewable energy systems generally should use multiple resources, such as sun and wind, to provide the most cost-effective system despite any cost difference between. In order to exploit these opportunities, the small wind turbine blade design must become increasingly multidimensional. Recent two-dimensional optimizations considered starting and Sessarego and Wood Renewables: Wind, Water, and Solar (2015) 2:9 power extraction (Wood 2011, Pourrajabian and Mirzaei 2014, and Shah et al 2014). The most powerful blade is the slowest to start and Clifton-Smith (2010) found that for blades of nearly equal power extraction, the quietest blade was the slowest to start whereas the fastest starting blade was the noisiest
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