Numerical Models and Design Loads for Wind Turbines under Downbursts
Abstract
Wind turbines are among the fastest-growing technologies for producing sustainable energy. In order to enhance efficiency, most wind turbines are built in rural locations where strong wind speeds are anticipated. These areas can be exposed to thunderstorms and extreme wind events, which are becoming more frequent and destructive owing to climate change. Downbursts are one of these events linked with thunderstorms, which occur in a sudden and localized manner. The wind loads specified in the wind turbine design codes are based on large-scale wind events and do not consider the effect of downbursts. As such, the current thesis aims to investigate the wind turbine behaviour under downburst wind effect. To achieve that, the numerical model, HIW-TUR, is developed incorporating a downburst wind field generated based on a previously developed Computational Fluid Dynamics (CFD) simulations, and a wind turbine structural model developed in this thesis to simulate the structural behaviour of the tower and blades. This numerical model is capable of predicting the quasi-static response of wind turbines under downbursts taking into consideration different downburst parameters (the jet diameter, the jet velocity, and the event location) as well as the change in the pitch angle of the blades. Dynamic response of wind turbines under downbursts is assessed using the open-source code, FAST, with two developed modules. These modules are responsible for introducing the downburst wind field into FAST and simulating the interaction between the downburst wind field and the wind turbine structure. Based on an extensive parametric study conducted using the developed numerical models, a complete set of design load provisions are proposed to simulate the critical effect of downbursts on the tower and the blades of generic wind turbines. Finally, HIW-TUR is extended to generate HIW-FARM to study a group of wind turbines under the effect of downbursts.