Abstract
Traditionally, circular cross-section towers have been used as supporting systems of wind turbines, but weaknesses have become apparent with recent upsizing of wind turbines. Thus, polygonal cross-section towers have been proposed and used in Europe. In this study, the effects of polygonal cross-sections on the aeroelastic and aerodynamic characteristics of wind turbines were examined through a series of wind tunnel tests. Aeroelastic tests showed that a square cross-section tower showed instability vibrations, and polygonal cross-section towers showed limited vibrations for tower-only cases. However, for wind turbines with various polygonal cross-section towers, no instability vibrations were observed, and displacements increased proportionally to the square of mean wind speed. Furthermore, pressure measurements showed that local force coefficients changed largely depending on wind direction and azimuth angle. Local drag force coefficients decreased with increasing number of tower sides, approaching those of the tower-only case, and local lift force coefficients showed larger absolute values than those of the tower-only case. The maximum mean and fluctuating drag force and the maximum fluctuating lift coefficients at each height decreased with increasing number of tower sides.
Highlights
Demand for renewable energy production has increased because of global climate change, and wind power potential is significant as an environmentally friendly energy resource
Fluctuating displacements near limited vibrations decreased with increasing number of sides, and the difference seemed to be small for the polygonal towers with number of sides larger than 10
As limited vibrations by vortex shedding were strongly related to vortex formation and shedding, it can be understood that vortex shedding weakened as the number of sides increased
Summary
Demand for renewable energy production has increased because of global climate change, and wind power potential is significant as an environmentally friendly energy resource. One of the most reliable methods, have been widely used to examine the aeroelastic and aerodynamic performance of wind turbines as well as electricity generation efficiency [3,4,5,6,7,8,9]. Limitations of circular cross-section towers with upsizing of wind turbines have become apparent, especially with regard to problems related to inadequate and uneconomic design strength. To solve these problems, researchers have proposed polygonal-cross-section towers, which have been used in Europe, but their wind-resistant performance has not been thoroughly investigated [10,11,12]. Strong wind speed that is higher than cut-out wind speed was assumed where the blades were in the feathered position
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