Theoretical and computational studies on the optimal positions of NACA airfoils used in horizontal axis wind turbine blades

Abstract

This paper presents a theoretical and computational study to determine the optimal positions of airfoils along the length of the horizontal axis wind turbine blade. We used four and five-digit NACA airfoils to model a 54-meter blade. The lift, drag coefficient, and lift-to-drag ratio of each airfoil are determined by using QBlade software. The aerodynamic performance of the airfoils is studied based on the blade element momentum theory, and Matlab software is used for numerical implementation. The velocity and pressure distributions on each airfoil are assessed using computational fluid dynamics. We implement the thickness distribution techniques to adjust the positions of the airfoils along the length of the blade. It is noted that stresses reach their maximum values at the root and minimum at the tip section. Thus, the thicker (NACA 4420) and thinner (NACA 23012) airfoils are set at 20% of the maximum chord and 91.11% at the tip sections of the blades. The remaining sections of the blade are configured using linear interpolation methods. Specifically, the maximum chord length of the new design is reduced by 18.06% compared to the NACA 23012 rotor blade. Finally, the recommended tip speed ratio for the designed rotor blade is estimated using the graphs of the normal and tangential forces, thereby producing a safe and efficient design.