Design of HAWT airfoils tailored for active flow control

Abstract

This study describes a methodology for designing airfoils suitable to employ actuation in a wind energy environment. The novel airfoil sections are baptized wind energy actuated profiles (WAP). A genetic algorithm-based multi-objective airfoil optimizer is formulated by setting two cost functions: one cost function for wind energy performance and the other representing actuation suitability. The wind energy cost function compares the candidate airfoils' performance with 'reference' wind energy airfoils, considering a probabilistic approach to include the effects of turbulence and wind shear. The actuation suitability cost function is developed considering horizontal axis wind turbines active stall control, including two different control strategies designated by 'enhanced' and 'decreased' performance. Two different actuation types are considered, namely, boundary layer transpiration and dielectric barrier discharge plasma. Results show that using WAP airfoils provides much higher control efficiency than adding actuation on reference wind energy airfoils, without detrimental effects in non-actuated operation. The WAP sections yield an actuator employment efficiency that is two to four times larger than those obtained with reference wind energy airfoils, at equivalent wind energy performance. Regarding geometry, and compared with typical wind energy airfoils, WAP sections for decreased performance display an upper surface concave aft region, while for increased performance, a convex upper surface aft region is obtained. The present study emphasizes that there is much to gain in designing airfoils from the beginning to include actuation effects, especially compared with employing actuation on already existing airfoils. The results demonstrate the potential of including actuation effects in the airfoil design process, thus enabling novel horizontal axis wind turbines control strategies.