Effect of non-ideally manufactured riblets on airfoil and wind turbine performance

Abstract

Riblets are a passive flow control method, which can be used for drag reduction, especially with small wind turbines that have a low Reynolds number. Riblet manufacturing, however, is a challenging task and the required production quality can cause extra barriers in terms of time and costs. If a relatively low-quality riblet structure could be successfully utilized in airfoils, it could enable wider adaptation of this particular flow control method. Public literature lacks studies that examine the applicability of non-ideally manufactured riblets on the ribleted airfoil. Therefore, in this study, Constant Temperature Anemometer and Particle Image Velocimetry are used to reveal the effect of non-ideal riblets on their performance and the flow field downstream of the airfoil. The measurements with a varying Reynolds number and incidence angle are conducted in the wind tunnel. The results indicate that, in the optimum conditions for the riblet design, the riblets reduce drag, thicken the boundary layer, reduce turbulence intensity, and weaken the mixing process. It is further demonstrated, that low-quality riblets have the potential to improve the performance of wind turbines, even when the riblet quality is lower than typically used.