Performance Analysis of a Large Vertical-Axis Wind Turbine in Gusty Wind Conditions

Vertical-axis wind turbines (VAWTs) could be a good alternative to horizontal axis turbines for offshore applications. However, the variability of the aerodynamic forces with the blade azimuthal position subjects the blade to fatigue stresses and generates typical power periodicity. Extreme wind conditions, such as gusts, could aggravate the aerodynamic load peaks, compromising the system durability. We analyze the transient aerodynamic loads generated under gusty winds for a 5 MW offshore troposkein-shaped VAWT. The behavior of the turbine at its equatorial plane is simulated by 2D-CFD assuming gusts characterized by different periods and amplitudes. Since the turbine is stall-regulated, a range of wind velocities going from the maximum efficiency velocity to the nominal power velocity are considered. The instantaneous overloads of power, blade radial force, and total force on the shaft are analyzed. An increase in the peak values up to 119% (power) and 51% (force on the shaft) are predicted relative to the most severe steady condition, depending on gust characteristics and the blade position when the gust crest occurs. These results refer to the equatorial plane, rather than the entire turbine. It is demonstrated how the passive stall load regulation method protects the turbine from excessive overloads.