CFD-RANS Study of Horizontal Axis Wind Turbines

This PhD project concerns the study of wind turbine aerodynamics with a CFD–RANS approach. Nowadays, industrial design codes for wind turbines are still based on the BEM (Blade Element Momentum) method, which has been extended with a number of empirical correction, often not based on physical flow features. The importance of accurate design does also increase as the machines tend to become larger. Therefore, the research is today focused more on the basic aerodynamic mechanisms. The general aim of this project was to get a better understanding of the physical behaviour of the flow field past wind turbine rotors, including the boundary layer flow as well as the wake region. Although CFD is not a practical design tool, useful suggestions for classical design methods can be derived from the analysis. A full three–dimensional CFD–RANS approach was used, modelling the whole rotor of a wind turbine by means of periodicity and in a moving reference system. All the simulations were performed using the finite–volume solution package Fluent®. A detailed selection of results is presented, dealing with the various investigated issues. A first validation of the computational methods was done by comparing the overall power production of a BEM-designed turbine. The most important features of the investigated machines were captured with CFD, so that a broad review of wind turbine aerodynamics was given, through the post processing of the computed solutions. A study on the blade root and tip was carried out, allowing to demonstrate the advantages of some recent improvements in rotor blade design, and showing the capabilities of CFD as an optimization method. Both the near and far wake were also analysed. Finally, the rotational effect on the boundary layer of rotating blades were studied, with generating a complete solution database and a post–processing tool. Further advancements are required, for stating more about the complex issues, as wake dynamics and rotational effects are. Nevertheless, the purpose of proving the capabilities of full–3D CFD–RANS for the study wind turbine aerodynamics has been fully achieved