Energy, vol.239, 2022 (SCI-Expanded)
© 2021 Elsevier LtdA passive flow control device with a local flexible membrane material over the suction surface was experimentally investigated with a smoke-wire experiment and time-dependent force measurement in this study. The experiments were performed on both the uncontrolled and the controlled FX 84-W-150 wind turbine airfoils applying the local flexible membrane at different locations first in the literature. The smoke-wire result for the uncontrolled airfoil indicated that a laminar separation bubble formed over the suction surface and the increasing incidence caused the short bubble at lower angles of attack to turn into the long bubble at moderate angles of attack by shifting upstream. After the experiment for the uncontrolled airfoil, six different locations of local flexibility were considered on the suction surface. All tests showed that applying the local flexibility especially at the leading edge ensured better aerodynamic performance. Additionally, it was observed that the lift coefficient was negatively affected when the length of local flexibility increased. As a result of these findings, employing the local flexibility between x/c = 0.2 and x/c = 0.4 over the suction surface was determined as the best optimum location and length. With employing this configuration, the laminar separation bubble was not only suppressed and eliminated but the fluctuations of the lift and the drag curves especially at moderate incidences were also decreased, resulting in increasing in aerodynamic performance as well as having less vibration and more stable on wind turbine airfoil. Apart from the studies regarding wind turbine airfoils with the local flexible material in the literature, our results bear witness that mounting this passive flow controller close to the leading edge and keeping it shorter was more influential in terms of the power output of wind turbine blades.