Design load provisions for simulating the critical effect of downbursts on wind turbines

Wind turbines are among the rapidly growing sources of sustainable energy. The review of design codes for this type of structure shows a lack of procedures for estimating the wind loads on wind turbines due to high-intensity wind events such as downbursts. There is a challenge in the analysis and design of wind turbines under downbursts because of the sudden and localized nature of such events, which makes the forces acting on the tower and blades dependent on the characteristics of the event. As such, the objective of the current study is to develop design load provisions that can simulate the critical effect of downbursts on wind turbines. These provisions are developed in two phases. Identifying the peak effects of the moving mean component of the downburst and determining the associated critical profiles are the aim of the first phase. To achieve this task, a comprehensive parametric study is conducted using the previously developed numerical model, HIW-TUR, on a wide range of wind turbine sizes and airfoil types in order to assess the critical response of wind turbines under the mean component of downbursts. The study takes into account the variations in the downburst size and its location relative to the tower center. Then, dynamic analyses under turbulence are conducted in the second phase using the open-source code, FAST, to determine a downburst gust response factor to magnify the effect of the mean component. The downburst gust response factor is then superimposed with the mean component profiles to present a complete set of design provisions. An example is presented to demonstrate the application of the developed loading provisions on a real wind turbine and to compare with the extreme synoptic wind load cases specified by the International Electro-technical Commission Loading Code.