Structural load analysis and optimization of the VAWT design

Abstract

The increasing global electricity consumption requires a corresponding increase in energy generation. Wind turbines generate electricity without depleting natural resources or emitting greenhouse gases, offering a straightforward solution to the energy dilemma. Wind power, because of recent technology breakthroughs, is a financially viable, clean, and quickly expanding source of energy. Traditional horizontal axis wind turbines (HAWTs) have been favored over the years due to a lack of research and development on vertical axis wind turbines (VAWTs). However, as wind turbines are deployed further offshore, conventional HAWTs begin to make less sense for floating platforms, as their high center of gravity can cause major tilting concerns.

VAWTs can be considered instead, as the rotor design can provide numerous possibilities to make them more commercially competitive than HAWTs. There is currently a lack of understanding of how specific design parameters influence the rotor configuration of modern VAWTs. This thesis attempts to identify design drivers for the VAWT design while accounting for their aerodynamic behavior and aeroelastic stability.

The VAWT is modeled in an aeroelastic analysis tool named HAWC2. First, the cross-sectional parameters of the blades and struts are determined using the BECAS software, which can be used as an input file for HAWC2. The original model is based on the reference model of Schelbergen, which is then verified. After that, several design factors are found and investigated to see how they affect the performance and behavior of the wind turbine. These design parameters include elements, such as the thickness of the laminate, the placement of the struts, and an additional diagonal strut. The study carries out a parametric analysis, to understand what can benefit an optimal VAWT design.

The verification phase shows that the reference model has significantly lower power output, most likely due to implementing a dynamic stall model in the aeroelastic analysis. The significance of proper modeling of the dynamic stall effects is highlighted. As with the reference model, a range of laminate thicknesses is provided, therefore, multiple models with different laminate thicknesses are examined. The assessment reveals that opting for thinner laminates can lead to reduced mass and expenses without significant power output compromise but with less structural integrity. Moreover, the optimal placement of the struts for increasing power output while preserving structural integrity can be identified through strut placement analysis. Besides, an additional diagonal strut shows enhanced structural stability but could be more expensive. The upscaling of the model is done by increasing the aspect ratio (with the blade length). The power generation is increased, but it is crucial to pay attention to the structural integrity and aeroelastic stability, as the deflection of the blades increases significantly. The study also looks into the Huisman VAWT design, which is compared to the company's own findings. The design is simplified but still shows good power output and blade behavior.

In short, this study examines the design drivers of the VAWT design, paving the way for advancing VAWTs in practical applications and future research.