Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article

Degree

Doctor of Philosophy

Program

Civil and Environmental Engineering

Supervisor

El Damatty, Ashraf

2nd Supervisor

Dai, Kaoshan

Affiliation

Sichuan University

Co-Supervisor

3rd Supervisor

Lu, Wensheng

Affiliation

Tongji University

Co-Supervisor

Abstract

The installation rate of wind turbines around the world is increasing significantly. Therefore, wind turbine farms are constructed in plentiful wind resources areas that put a considerable number of wind turbine towers under severe wind conditions. As a result, failures due to unexpected wind loads on either the blades or the tower are increasing. In addition, wind turbines are designed to resist synoptic wind loads as per the current guidelines, which do not consider high-intensity wind (HIW) events such as tornadoes. The built-in-house numerical code “HIW-WT” has been developed in this study to model wind turbines under three-dimensional wind fields such as tornadoes. Extensive analysis has been conducted with the goal of determining the critical tornado wind field for wind turbines considering different tornado structures. The methodology depends on identifying the critical location of the tornado that will cause peak straining actions on the tower and blades, and the optimal pitch angle that will minimize the effects of that tornado. Design wind profiles for tornadoes are developed in this study taking into account several factors. The proposed wind profiles are presented as wind speeds in the rotor plane and perpendicular to the rotor plane at different heights. The development of the tornado design wind profile took into consideration several tornado wind fields with different tornadic structures. It also accounted for the configuration of the blades (pitch angle changes), various airfoil sections, the rotor configuration (yaw angle changes), the supporting tower’s height (hub height), and the base diameter of the supporting tower. The proposed wind profile can be applied on wind turbines by design engineers for tornado hazard assessment and it has the potential to be implemented in structural design codes and guidelines for future designs.

Summary for Lay Audience

Wind turbines are usually steel hollow structures that can be vulnerable to dramatic failures due to High-Intensity Wind (HIW) events, which are classified as a category of localized windstorms that includes tornadoes and downbursts. Analyzing Wind Turbines (WT) under tornadoes is a challenging-to-achieve task because tornadoes are much more complicated wind fields compared with the synoptic boundary layer wind fields considering that the tornado’s 3-D velocity components vary largely in space. As a result, the supporting tower of the wind turbine and the blades will experience different velocities depending on the location of the event. Wind farms also extend over a large area so that the probability of a localized windstorm event impacting one or more towers is relatively high. Therefore, the built-in-house numerical code “HIW-WT” has been developed to predict the straining actions on the blades considering the variability of the tornado’s location and the blades’ pitch angle. The developed HIWWT numerical model incorporates different wind fields that were generated from developed CFD models. Design wind profiles for tornadoes are developed in this study taking into account several factors such as blades configuration, airfoil sections, the rotor configuration, the supporting tower’s height, and the base diameter of the supporting tower. Generally, it has been found that F2 tornado wind fields present a threat for wind turbines and must therefore be taken into account if the hazardous tornadic effect on the tower elements is to be avoided. This goal can be reached by implementing the recommended wind profiles into the current design codes and guidelines.

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