Aerodynamic Performance and Annual Energy Production of Small Horizontal Axis Windmill Using Different Airfoils

Wind energy is considered as a clean energy source of dominated technology and well accepted by the populations. The literature shows more than 80 countries having wind installations and there is the expectation to have expanded investments to about U$ 3.6 trillion until 2040. High capacity wind generators are well developed and usually installed offshore where the wind velocity is relatively high and constant over most of the year. On the other hand, small windmills are usually installed for individual and community use in urban and isolated areas. These machines are usually supposed to generate energy at relatively low wind speeds, have simple construction and relatively low maintenance cost. This paper seeks to determine the aerodynamic performance and annual energy production for small horizontal axis windmill of 10 kW nominal power using airfoil of families NACA, Gottingen and Selig. The formulation of the aerodynamic model is based on the combined momentum and blade element theory. A numerical code is developed and validated against available numerical results showing good agreement. From the numerical predictions, it was found that for nominal speed of 10 m/s Gottingen airfoil produced the highest amount of energy. Further numerical investigation was realized to determine details of the rotor blades such as chord and twist angle distributions along the blade, variation of the axial and tangential induction factors and distributions of thrust and torque along the blade length. The results indicated that the Gottingen airfoil GO482 produced the highest values of coefficient of power and the biggest annual energy production in comparison with the investigated NACA and Selig airfoils. Because of this good performance it can be recommended for small windmills applications.