Effects of the height and chordwise installation of the vane-type vortex generators on the unsteady aerodynamics of a wind turbine airfoil undergoing dynamic stall

Abstract

Dynamic stall can produce nonlinear and unsteady aerodynamic loads on wind turbines. It has attracted considerable attention recently by introducing vortex generators (VGs) to suppress the dynamic stall, although the effects of decisive VG parameters have not yet been investigated adequately. This paper aims to provide insights into the impacts of vane height and chordwise installation on the dynamic stall phenomenon of an NREL S809 airfoil equipped with VGs. Unsteady flow characteristics are identified through fully resolved URANS simulations. Unsteady flow separation can be suppressed effectively via the VG-induced streamwise vortices. Consequently, the delayed onset of dynamic stall leads to greatly increased maximum lift and accelerated flow reattachment in the downstroke process. Low-profile VGs can cause an early abrupt dynamic stall and remarkable aerodynamic hysteresis, thereby losing their effectiveness. Moreover, positioning VGs too far downstream can cause significant increases in both drag and hysteresis intensity, because the streamwise vortices decay rapidly under the high adverse pressure gradient. Increasing VG size and utilizing double-row VGs simultaneously can strengthen the VG-induced streamwise vortices and hence the boundary layer momentum transfer, resulting in effectively controlled local flow structures. Furthermore, double-row VGs perform efficiently in improving unsteady aerodynamics due to low drag penalty.