Development of a software tool for the calculation of the main horizontal wind turbine blade aerodynamic parameters

Abstract

In Chapter 1, Introduction, a concise reference to the categories of the wind turbines is presented together with the scope of this Thesis and the theoretical background which is necessary to meet this scope. A literature overview is also presented. In Chapter 2, Aerodynamics of Wind Turbines, one dimensional Momentum theory is applied to an annular control volume for the determination of the thrust and torque applied on an annular cross section area as a function of the flow conditions. Also there is a presentation of the airfoil’s nomenclature and their lift and drag characteristics. In Chapter 3, Blade Design for Horizontal Axis Wind Turbines, after the actual blade profile is separated into elements of equal length, blade element theory is applied to each blade element for the determination of the forces applied at each element for specific flow conditions, taking into consideration the effects of rotor’s geometry characteristics, including chord and twist distributions. Betz’s and Schmitz’s methods are applied to calculate the chord length and pitch angle distributions. Blade Element Momentum (BEM) or Strip theory is used for the calculation of the axial and angular induction factors taking into consideration the tip loss effect. An iterative process is necessary for the calculation of the axial and angular induction factors and the performance of the rotor. The originality of this Thesis lies in the fact that, three different approaches from the relevant literature are used in the same work for the accomplishment of the iteration process and afterwards the results are compared against data from a commercial wind turbine. A Visual Basic tool to perform calculations has been developed. In Chapter 4, The Calculation Tool, pitch and stall regulation are briefly presented. Afterwards the airfoil profile is clarified, with NACA 44XX series being our choice. Guides for the usage of the tool and the choice of the necessary input data values are given and the functions of the tool, through its Excel interface are presented. In Chapter 5, Results, the optimal blade chord length and pitch angle distributions are calculated as well as the rotor’s performance at the design conditions. The evaluation of the tool follows, for each one of the three approaches used for the iteration process versus Vestas V52 and finally a parametric analysis is made for different number of blades. In Chapter 6, Conclusions-Recommendations, a synopsis of the basic findings is presented. Finally, recommendations for future work are given.