Effect of steady and quasi-unsteady wind on performance of horizontal axis wind turbines

The effect of steady and quasi-unsteady wind flow on the performance of a horizontal axis wind turbine was investigated. First, the initial design of the blades was carried out in steady conditions, and then by defining a random number generator function, fluctuations of wind speed were considered. The results indicate that the output power in quasi-unsteady conditions is lower than that in steady. The difference in output power was significant, approximately 4.3%, at the highest studied turbulence intensity. Comparing the difference percentage between the maximum and minimum power coefficient of quasi-unsteady and initial power coefficient of steady conditions, showed that the effect of wind speed fluctuations is greater in the root and tip regions. Seven airfoils were used in this study. Using one type of airfoils or a combination of 2–7 airfoils along the spanwise were considered, and the best combination resulting the lowest effect of wind speed fluctuations was obtained. It was also observed that for maximizing the power coefficient, using the RISØ-A1–18 airfoil for the root to tip is the best option, and then using the combination of RISØ-A1–24, DU 93-W-210, and RISØ-A1–21 airfoils with a specific order of use is the next best option.