Optimized design of aerodynamic airfoils for vertical axis wind turbines" "diseño optimizado de perfiles aeorodinámicos para su utilización en turbinas eólicas de eje vertical

Abstract

Abstract The current world context demands a change towards environmentally friendly energy sources. Luckily, the interest on renewable energy sources has been constantly increasing over the past years. Nowadays, wind energy represents one of the most economical options, employing a totally mature harvesting technology. Due to their higher energy output, horizontal-axis wind turbines have been traditionally the preferred option. Nevertheless, vertical-axis wind turbines are becoming relevant, specially in urban areas. Their advantages evidence the need of further research to overcome the main drawbacks that prevent their implantation. The main objective of this thesis is the development of scientific-technological knowledge applicable to the design of optimized vertical-axis wind turbines. As an ultimate goal, transfer of this knowledge is foreseen to small and medium-sized enterprises. Firstly, a literature survey about wind power extraction systems has been performed, focusing afterwards in vertical-axis wind turbines, their advantages, disadvantages and research interest. Then, the design and analysis techniques applicable to vertical-axis wind turbines have been reviewed. Afterwards, an analytical model based on streamtube theory has been developed to predict the performance of prospective turbine designs, being able to predict the whole power curve in computational times in the order of minutes. The model has been used to analyze the influencing parameters in the turbine performance, proposing optimal values of these parameters and the optimal characteristics that an airfoil should possess to be suitable for practical applications of these turbines. Subsequently, the focus has been set on Computational Fluid Dynamics models for the study of the aerodynamic performance and the flow field developed by both a vertical-axis wind turbine and an isolate typical turbine airfoil. Guidelines for the numerical simulation of both turbines and airfoils are provided. Additionally, the main flow unsteadiness generation mechanisms, flow field regions and instabilities have been identified. Insight into the loss of performance of these turbines due to fluid dynamics phenomena has been also provided. Finally, all the generated knowledge has been applied to the design of a small-scale turbine model, developing a procedure for the in-house fabrication of turbine blades and an experimental procedure to estimate the aerodynamic performance of the turbine. Hot-wire measurements have been performed in the turbine wake. The experimental results have verified the methodologies developed in this thesis. Finally, the main findings and implications of this study are discussed, and future research possibilities are outlined.