Extreme gusts and their role in wind turbine design

Wind turbines are the largest rotating machines on the planet, operating in some of the most remote and hostile areas. During a lifespan of several decades, they have to withstand storms, waves, and gusts (and preferably produce electricity in the process). Yet, designers cannot make them too strong. Every additional kilogram of mass has to be manufactured, transported, and installed, and has a price tag that is directly added to the cost of energy. Optimizing structures, however, is very challenging. It requires designers to predict the highest loads on wind turbines, after they have spent decades in a turbulent wind climate. This PhD research focused on extreme wind gusts, which are among the most severe events that a wind turbine can encounter. The concept of a gust is extended from its common perception to a complete mathematical model of three-dimensional velocity fields. These fields have proven to be very valuable to the design process, since they offer a unique insight into the conditions in which high loads are triggered. Moreover, they can be used to efficiently predict the long-term loads with low uncertainty. At the same time, this physical gust model helps to answer an important question for future wind turbines: what happens when rotor blades outgrow the size of the most severe gusts in the atmosphere?