The Effect of rotor size on the teeter behavior of two-bladed wind turbines

Abstract

The rotor of a two-bladed turbine allows the implementation of an additional degree of freedom around the rotating hub y-axis. This idea is over 60 years old, and various research and commercial turbines have had a teeter hinge. Fatigue and extreme loads can be reduced significantly with a teeter hinge. Teetered turbines have been mainly below or around a rotor diameter of 100 m, and most of the teetered turbines have been built in the 1980s. Today, rotor blades have become much larger and, in relation to their sizes, lighter (indicated by the Lock number, the ratio of aerodynamic, and inertia forces). Both have an impact on teeter dynamics. This paper investigates the effects of teeter behavior over a wide range of turbine sizes using the analytical equations of the teeter movement combined with numerical simulations of the CART2 (600 kW), 2-B Energy's 2B6 (6 MW), and the 2B20HAW-T (20 MW, based on the INNWIND.eu turbine). It extends the existing teeter equations by the effects of pitch-teeter-velocity coupling and concludes that modern turbines with a high Lock number show a significant increase in aerodynamic damping, which leads to a different teeter behavior, making this rather old turbine concept worth considering in more detail.