Experimental investigation of a pitch-oscillating wind turbine airfoil with vortex generators

Abstract

The inflow shear and turbulence, tilt or yaw misalignment, and tower passage lead to dynamic stall on turbine blades. The effects of vortex generators (VGs) on the aerodynamic performance of a typical wind turbine airfoil, namely, DU91-W2-250, are measured under the background that VGs are gradually and widely installed for energy improvement. The experiment is carried out in a wind tunnel at the Reynolds number of 3×105. The oscillation of the testing model is driven by a servo motor, and the aerodynamic performance is measured using an ESP-64 scanner. The flow separation is visualized with tufts. The obtained results show that the installation of the VGs could effectively control both static stall and dynamic stall of the airfoil because VGs cause a lower pressure region on the airfoil suction surface near the leading edge and a pressure plateau that appears later than in the smooth airfoil. Meanwhile, the VGs could effectively increase the adverse pressure gradient and lead to an early transition to delay the flow separation before stall and force the flow field in the turbulence state. It is also found that the VGs could reduce the pressure fluctuations caused by the turbulence of the boundary layer during dynamic stall. Furthermore, the VGs are also found to be useful in suppressing the span-wise movement of vortices. However, the VGs could not improve the aerodynamic performance in the deep stall region under none of the static and dynamic conditions.