Investigation of aerodynamic performance ofpitch-control wind turbine with polygonal towers

Wind turbines are commonly used power generation systems around the world and their application is becoming increasingly widespread. Traditionally, they have been mounted on circular towers, but their recent upsizing has exposed weaknesses of these structures, including problems related to manufacturing and insufficient strength. Thus, the concept of site-assembled modular towers with polygonal cross-sections has been proposed, but their aerodynamic performances have not been properly investigated. In the present study, the aerodynamic performances of a wind turbine with seven polygonal towers were investigated. Wind tunnel tests have shown that the forces on the upper structure (rotor and nacelle) are larger than those on the tower, which makes the effect of cross-sectional shape of tower relatively small. Drag forces decrease with increasing number of sides of the tower, and lift forces on the square helical tower are quite small. For the power spectra, there are peaks in high reduced frequency for oblique wind directions at azimuth angles of 60° and 90°, which were considered to result from vortices that were formed and shed behind the blade in front of the tower.